Photopolymerization of Poly(ethylene glycol) dimethacrylates: The influence of ionic liquids on the formulation and the properties of the resultant polymer materials

Photopolymerization of Poly(ethylene glycol) Dimethacrylates: The

Influence of Ionic Liquids on the Formulation and the Properties

of the Resultant Polymer Materials

1

2

SERGEY A. CHESNOKOV, MARYA YU. ZAKHARINA, ALEXANDER S. SHAPLOV, ELENA I. LOZINSKAYA,

3

1

4

2

INNA A. MALYSHKINA, GLEB A. ABAKUMOV, FREDERIC VIDAL, YAKOV S. VYGODSKII

1

G. A. Razuvaev Institute of Metalloorganic Chemistry Russian Academy of Sciences (IOMC RAS), Tropinin str. 49,

Nizhnii Novgorod 603950, Russia

2

A. N. Nesmeyanov Institute of Organoelement Compounds Russian Academy of Sciences (INEOS RAS), Vavilov str. 28,

Moscow 119991, GSP-1, Russia

3

Department of Physics, Moscow State University, Vorob’evy gory, Moscow 119992, Russia

4

Laboratoire de Physico-chimie des Polym e` res et des Interfaces (LPPI), Universite’ de Cergy-Pontoise, 5 mail Gay-Lussac,

Cergy-Pontoise Cedex 95031, France

Received 13 December 2009; accepted 6 March 2010

DOI: 10.1002/pola.24008

Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: The photo-initiated polymerization of poly(ethylene

glycol)dimethacrylates [PEGDM(n)] in the presence of various

ionic liquids (ILs) is reported. The influence of ILs concentra-

tions as well as of their nature upon the photopolymerization

kinetics was studied in detail. It was found that according to re-

active ability in bulk and in solution photopolymerization, the

investigated monomers can be divided into two groups:

PEGDM(1)–PEGDM(2)–PEGDM(3) and PEGDM(4)–PEGDM(7-8).

ILs slightly influence the photopolymerization of monomers

from the first group and greatly change kinetics of those from

the second. Such behavior was explained by the theory of

derived from low reactive monomers. Relying on the obtained

data, the attempt to predict the structure of the ‘‘best’’ ionic addi-

tive for the given monomer photopolymerization was performed

and proved. Finally, the influence of both residual and specially

added ILs quantities upon the properties of obtained polymer

materials was investigated. It was revealed that ILs can physi-

cally interact with polymer networks increasing their thermal

stability, plasticizing films, and blocks, imparting ionic conduc-

tivity equal up to 3.62 ꢀ 10^ꢁSm/cm at 25 C. VC 2010 Wiley Peri-

3

ꢂ

odicals, Inc. J Polym Sci Part A: Polym Chem 48: 2388–2409, 2010

‘

‘kinetically favorable or unfavorable monomer associations.’’ It

KEYWORDS: catalysis; ionic liquids; kinetics (polym.); oligomers;

photopolymerization; polyethylene glycol dimethacrylates;

polymerization kinetics

was demonstrated that certain ILs accelerate the photopolymeri-

zation of the highest PEGDMs and offer access to the polymers

INTRODUCTION Photopolymerization of unsaturated mono-

mers is well established and is a convenient method that

allows polymerization at temperatures which are inapplica-

ble for other types of initiation. Photopolymerizable compo-

sitions (PPC), nowadays, have been intensively used in a

wide range of modern techniques such as polygraphy, elec-

tronics, optic applications, stereolithography, and prosthetic

intriguing place (ILs definition, properties, and application

2

–7

can be found elsewhere ). They have already demonstrated

a number of advantages in various types of polymerization

2

processes. In such a way, higher overall rates of radical poly-

merization as well as higher molecular weights of obtained

polymers were observed in ILs in comparison with tradi-

8

–12

tional organic solvents.

gation rate constant (k

It was also found that the propa-

) in the radical polymerization of

1

dentistry. Such increasing demand for new materials leads

p

to the necessity for the development of novel monomers and

simultaneously to the deeper investigation of polymerization

mechanisms including the influence of initiator nature, addi-

tives, etc.

methyl methacrylate in typical IL, namely in 1-butyl-3-meth-

ylimidazolium hexafluorophosphate ([1-CH -3-C H im][PF ]),

3

4

9

6

is higher than that in bulk, whereas the termination rate

13,14

constant (k ) is considerably lower.

Because of the ability

t

As novel candidates among additives for the improvement of

both the photopolymerization reaction rate and monomers

conversion, ionic liquids (ILs), can occupy a separate, quite

to dissolve both the monomers and catalysts, thus simplify-

ing the system, as well as to gain the control over the molec-

ular weight and polydispersity, ILs were discovered

Additional Supporting Information may be found in the online version of this article. Correspondence to: S. A. Chesnokov (E-mail: sch@iomc.ras.ru)

or A. S. Shaplov (E-mail: zipper@ineos.ac.ru)

Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 2388–2409 (2010) V

2010 Wiley Periodicals, Inc.

C

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ARTICLE

1

5–17

especially attractive in ATRP process.

The nitroxide-

1-methylimidazole (99%, Aldrich), 1-methylpyrrolidine

(98%, Acros), N-methylmorpholine (99%, Aldrich), pyridine

(99%, Acros), and 1,2-dimethylimidazole (98%, Aldrich)

mediated controlled polymerization of methyl acrylate hap-

pened in ILs with an increased rate when compared to tradi-

1

8

tional organic solvents.

Higher rates of polymerization

were distilled under inert atmosphere from CaH . Reagent-

2

along with narrow polydispersity of obtained polymers were

also observed in the reversible addition-fragmentation chain

transfer polymerization of methacrylate and acrylate mono-

grade chloroform, methylene chloride, benzene, and metha-

nol were obtained from Aldrich (Germany) or Merck (Ger-

many) and were dried by vacuum distillation over P O and

2

5

1

9

mers. A similar increase in the polymerization rate was

found in the radiation-initiated polymerization of methyl

magnesium pellets plus iodide, respectively.

2

0

Monomers

methacrylate and charge-transfer polymerization of methyl

2

1

Monoethylene glycol dimethacrylate [PEGDM(1), Reper-NN,

8%], triethylene glycol dimethacrylate [PEGDM(3), Reper-

NN, >97%], tetraethylene glycol dimethacrylate [PEGDM(4),

¼ 330 g/mol, Aldrich, ꢃ97%], and polyethylene glycol

dimethacrylate [PEGDM(7-8), M

¼ 550 g/mol, Aldrich,

methacrylate. However, the number of publications dealing

with the investigation of ILs influence upon the photopoly-

9

2

2,23

merization process is rather limited. Thus, it is known,

M

n

that some ionic monomers, derived from neutralization reac-

tions of acrylic or methacrylic acids and different trialkyl-

amines, show moderate increase in photopolymerization

rates compared to their unmodified analogs. Along with that,

the addition of classical tetrafluoroborate or triflate imidazo-

lium ILs to uncharged prevalent methacrylate monomers

n

ꢃ97%] (Scheme 2) were purified before use in accordance

2

7

with the published standard procedure : the benzene solu-

tion (1:1) of the monomer was three times extracted with

1% aqueous KOH and afterwards was thoroughly washed

2

4,25

with distilled water. The benzene solution was then dried

highly increases their photopolymerization rate.

Simulta-

2

6

over CaCl

2

, filtered, and passed through the chromatographic

neously, it was demonstrated by our group that photopoly-

merization of triethylene glycol dimethacrylate [PEGDM(3)]

and polyethylene glycol dimethacrylate with 7.5 oxyethylene

units [PEGDM(7-8)] in the presence of various ILs proceeds

ꢂ

column filled with alumina preliminarily calcined at 400 C.

By use of NMR spectroscopy, it was found that the average

number of oxyethylene units (n) in PEGDM(7-8) was equal

to 7.5.

2

6

in a different way. It was found that imidazolium ILs accel-

erate PEGDM(3) photopolymerization and suppress the poly-

merization of PEGDM(7-8). In contrast, polymerization of

PEGDM(7-8) with extra small amounts of phosphonium ionic

solvents proceeded with high rate and offered access to the

new polymers and the use of low reactivity monomers in

PPC.

Diethylene glycol dimethacrylate [PEGDM(2)] was synthe-

sized in accordance with the procedure listed in the litera-

2

7

ture. Diethylene glycol (10.3 g, 0.096 mol) and triethyl-

amine (23.5 g, 0.233 mol) were dissolved in 80 mL of dry

tetrahydrofuran. To the prepared solution at room tempera-

ture, 20.3 g (0.194 mol) of freshly distilled methacryloyl

chloride were added dropwise under inert atmosphere. The

2

6

This article deals with the continuation of our work on the

acceleration of photopolymerization by the addition of ILs.

The attempt to understand and clarify the effect of the ionic

liquid’s nature upon the photopolymerization process is per-

formed on the basis of a large set of dimethacrylate mono-

mers and various ionic solvents. Several factors are sug-

gested and tested for the explanation of observed ILs

influence. Among the latter are the theory of kinetically

favorable and adverse monomer associations, anion size, and

coordinating ability, aromatic or aliphatic nature of the used

cation. Finally, the impact of both the residual and specially

added amounts of ILs upon the properties of obtained poly-

mer materials is investigated in details.

ꢂ

reaction mixture was heated up to 80 C and was held at

this temperature for 1.5 h. Then, it was cooled down to

room temperature and the precipitate, namely, triethylammo-

nium chloride, was filtered off. Tetrahydrofuran was evapo-

rated at room temperature under reduced pressure and the

resultant product was obtained as slightly yellow oil. It was

then purified according to the well known published

2

7

procedure.

Yield: 20.5 g (88%); NMR (300.15 MHz, CDCl ): d ¼ 1.95 (s,

3

6H, ¼¼ CACH ); 3.65–3.80 (m, 4H, CH OCH ); 4.25–4.43 (m,

3

2

4H, C(O)OCH A); 5.54–5.62 (m, 2H, CH ¼¼ C(CH )A); 6.1–

2

3

6.15 (m, 2H, CH ¼¼ C(CH )A); IR (KBr pellet): 3425 (w),

2

3

3106 (w, m

), 2958 (s, m

), 2929 (s, m

), 1785 (m),

CAH

1

720 (vs, m ), 1638 (s, m ), 1454 (s), 1404 (m), 1378

EXPERIMENTAL

C¼O

C¼C

(

m), 1320 (vs), 1297 (vs), 1251 (m), 1171 (vs), 1136 (vs),

Materials

1

047 (s), 1005 (m), 943 (s), 882 (m), 880 (w), 815 (m), 700

Lithium bis(trifluoromethylsulfonyl)imide (99%, Fluka), am-

monium trifluoromethanesulfonate (98%, Aldrich), ammo-

nium tetrafluoroborate (99%, Aldrich), potassium hexafluor-

ophosphate (98%, Aldrich), potassium hexafluoroantimonate

ꢁ1

(

w), 655 (m) cm

.

Ionic Liquids

All imidazolium, pyrrolidinium, ammonium, and morpholi-

nium bromide ILs were synthesized according to improved

procedures

(

98%, Aldrich), silver acetate (99%, Fluka), silver nitrate

99%, Fluka), sodium dicyanamide (98%, Acros), anhydrous

2

8,29

4

differing from the known ones by mild con-

Na

2

SO

4

(>98.5%, KMF Laborchemie Hadels GmbH), phos-

ditions, which allowed the preparation of colorless high pu-

rity ionic media. Further reactions of ionic exchange were

performed with corresponding sodium, potassium, or silver

phorus pentoxide (>98%, Fluka), 9,10-phenanthrene qui-

none (PQ, Acros Organics, 98%), and CaH₂(98%, Aldrich)

were used as received. All alkyl bromides (Acros Organics),

3

0–34

salts as described in detail elsewhere.

Synthesized ILs

PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

(

Scheme 2) were characterized by elemental and Karl Fisher

usage of any color filters. The distance between the polymer-

ized composition and the focusing equipment was fixed at

60 cm.

analysis, NMR and IR spectroscopy before use. The purity of

ILs was estimated by mentioned methods to be higher than

98%.

Photopolymerization Kinetics

Tetradecyltrihexylphosphonium chloride (P[(C H ) (C H )]Cl)

6

13 3 14 29

Photopolymerization kinetics of examined monomers was

and bromide ([P(C H ) (C H )]Br) ILs were received from

6

13 3 14 29

3

5

investigated by thermographic analysis upon the use of PQ

as photoinitiator. The desired amount of chosen IL was

mixed with the certain monomer, whereupon 0.2 wt % of PQ

was added. The reaction mass was stirred until the forma-

tion of a homogeneous solution. The latter was transferred

into the glass ampoule with 4.5 mm diameter (the thickness

of the ampoule wall was 0.5 mm), then sealed under high

vacuum (until the residual pressure in the ampoule became

Cytec (Cytec Canada), whereas tetradecyltrihexylphosphonium

tris(pentafluoroethyl)trifluorophosphate ([P(C H ) (C H )]

6

13 3 14 29

(

CF CF ) PF ) and tetradecyltrihexylammonium bromide

3

2 3

3

6 13 3

[N(C H ) (C14H29)]Br) were obtained from Merck KGaA

Darmstadt, Germany, LSA R&D LSS S&TS, Ionic Liquids

Research Laboratory) and were used after careful drying for

ꢂ

7

–8 h at 55 C under high vacuum with a special flask filled

with P O and introduced into the vacuum line.

2

5

ꢁ

2

equal to 10 mmHg) and placed into the recording cell of

the thermographic apparatus at constant temperature for

further irradiation. The temperature of the photopolymeriza-

Procedure for the Preparation of Starting Bromide IL

Freshly distilled N-methylmorpholine (28.89 g, 0.286 mol)

was dissolved in 60 mL of dry methanol. The solution was

ꢂ

tion was kept equal to 25 C, at that, during the polymeriza-

tion the temperature inside the studied sample can differ

ꢂ

cooled down to 0–2 C in an ice bath. Afterward, the solu-

ꢂ

not more than in 1 C. Photopolymerization was carried out

tion of ethylbromide (31.97 mL, 0.428 mol) in 20 mL of dry

methanol was slowly added dropwise to the intensively

stirred reaction mixture under inert atmosphere. The reac-

by use of tungsten lamp KGM 24-250 with a heat filter and

focusing equipment. The second ampoule with the corre-

sponding polymerized composition was used as a reference

pattern. The polymerization conditions described above were

close to the isothermal ones. The obtained samples possess

cylindrical form with the height of 1.5 cm. The weight of the

loaded reaction mass and, respectively, of the obtained poly-

mer sample constitutes to 0.12–0.14 g.

ꢂ

tion mass was kept at 0–2 C for 12 h under stirring and

inert atmosphere. Then, the temperature was raised step-

ꢂ

wise: to 25 C for 12 h, to 40 C for 24 h, and finally to 50–

5

ꢂ

5 C for 48 h. After the reaction completion, methanol and

the excess of ethylbromide were removed under reduced

ꢂ

pressure at 40 C/12 mm. The resultant product as white

The obtained thermographic curves were used for calcula-

tion of monomer conversions and subsequent construction

of polymerization kinetics curves. The thermographic analyti-

cal method is based on the measurement of the time de-

pendent heat evolution that corresponds to the reaction of

crystals was washed several times with pure acetone and

ꢂ

then finally dried at 40 C/12 mm for 6 h and at 40 C/1–2

mm for 12 h with a special flask filled with P O and intro-

2

5

duced into the vacuum line. The obtained N-methyl-N-ethyl-

morpholinium bromide ([N-CH -N-C H morph]Br) was highly

3

2 5

3

5

the definite quantity of the monomer double bonds. The

thermographic curve, which is the full analog of the polymer-

ization rate/time dependence, is registered during the photo-

polymerization process and then undergoes the integration,

which in its turn leads to the determination of the monomer

hygroscopic.

Yield: 55.62 g (93%); water content according to Karl Fisher

analysis is 0.65 wt %; m.p. 182–184 C; Anal. Calcd for

ꢂ

C H NBrO (209.98): C, 40.01%; H, 7.68%; N, 6.67%; Found:

7

16

1

C, 39.84%; H, 7.83%; N, 6.58%; H NMR (300.15 MHz, DMF-

conversion at any chosen period of time. The theoretical po-

7

d ): d ¼ 1.63 (t, 3H, J ¼ 7.2 Hz, NCH CH ), 3.65 (s, 3H,

35–45

HH

2

3

lymerization heat value equal to 56 kJ/mol

was used as

NCH ), 3.94 (m, 4H, NCH CH O), 4.11 (q, 2H, J ¼ 7.5 Hz,

3

2

HH

a reference for the aforementioned calculations. Each poly-

merization kinetics curve is an average result of the five

runs that can differ in maximum polymerization reduced

rate (W_m_a_x) and in maximum conversion not more than in

1

3

NCH CH ), 4.33 (m, 4H, NCH CH O); C NMR (100.61 MHz,

2

3

2

7

DMF-d ): d ¼ 7.2 (NCH

2 3 3 2 2

CH ), 46.0 (NCH ), 59.3 (NCH CH O),

6

0.2 (NCH CH ), 60.6 (NCH CH O); IR (KBr pellet): 2970

2

3

2

(

1

(

vs, m_C_A_H_a_l_i_p_h_a_t_i_c), 2881 (s), 2074 (w), 1634 (m), 1475 (vs),

461 (vs), 1431 (s), 1401 (w), 1305 (m), 1276 (m), 1239

w), 1206 (w), 1180 (m), 1135 (vs), 1109 (vs), 1091 (s),

5%.

Films Preparation

1

065 (m), 1021 (m), 954 (m), 884 (vs), 851 (w), 810 (w),

ꢁ

1

Pure films or films incorporating ILs inside (Scheme 1) were

prepared by analogy with the following procedure given for

the film bearing 50 wt % of IL: 0.50 g (0.0009 mol) of

PEGDM(7-8), 0.50 g (0.0021 mol) of [1-CH -3-C H im](CF

618 (m) cm

.

Photopolymerization

3

2

5

3-

All photopolymerization reactions were carried out under

the tungsten lamp KGM 24-250 (24 V; 250 W, Russia) with a

heat filter and focusing equipment, having intensity of lumi-

nous flux equal to 40 kLx. The light emission lies in the

range of 400–750 nm, which corresponds to the visible

region. Irradiation was performed by full light without the

SO ) N and 0.002 g of PQ were mixed together at room tem-

2 2

perature until the formation of clear solution. The obtained

solution was poured into a mold made from two glass plates

clamped together and sealed with a 250 or 500 lm thick

V

R

Teflon gasket. Afterward, the mold was placed in front of

the lamp within 40 cm distance and was treated with light

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INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE

RESULTS AND DISCUSSIONS

Polyethylene Glycol Dimethacrylates

Photopolymerization

The investigation of polymerization process of different dime-

thacrylate monomers and oligomers revealed the presence of

relatively stable associative molecular structures, which are

SCHEME 1 The visual presentation of polymer film and poly-

mer block.

3

9,40

usually formed in liquid oligomers.

It was proved that such

associates impact the physical properties of corresponding

monomers as well as the kinetic parameters of their polymer-

for 1.5 h. The resultant crosslinked film was taken out from

the mold and was used for further investigations.

3

9,40

41,42

ization.

The studies

on anomalous influence (the multi-

ple acceleration or suppression of the monomer polymeriza-

tion) of the small additives of different compounds upon the

polymerization of higher alkyl(meth)acrylates allowed to for-

mulate the model of ‘‘kinetically favorable monomer associa-

Synthesis of Polymer Blocks

Pure polymer blocks and those, with mentioned amount of

ILs (Scheme 1), were prepared according to the procedure

described for photopolymerization kinetics (see vide supra)

with the exception that the diameter of ampoule was equal

to 120 mm and no reference pattern was used.

4

3

tions.’’ According to this theory, the mutual orientation of the

molecules inside the associate can be either identical to that in

the activated (transition) complex of chain growth reactions or

not. In the first case, polymer chain growth inside the associate

will run faster than in the absence of any associations, and the

associate can be considered as kinetically favorable packing of

molecules. In contrast to that, the second instance leads to the

slow polymer chain growth, and the corresponding associate is

regarded as kinetically adverse mutual molecular orientation.

Measurements

NMR data were obtained at 300.15 MHz for proton, 75.04

MHz for carbon, 161.97 MHz for phosphorous, and at 282.40

MHz working frequency for fluorine in the indicated solvent

ꢂ

at 25 C on a Bruker AMX-300 spectrometer and are listed

4

1,42

Thus, according to the kinetic experiments

as well as to the

in ppm downfield from tetramethylsilane. The Nicolet

Magna-750 Fourier IR-spectrometer was used to record IR

spectra. Electronic absorption spectra of PQ solutions in

PEGDM monomers were obtained from UV/VIS Perkin–Elmer

4

computer modeling it was established that higher methacry-

lates form kinetically adverse associates.

2

6

In previous work, it was found that the photopolymeriza-

tion of polyethylene glycol dimethacrylates in the presence

of ILs proceeds in a different way compared to bulk photo-

polymerization. The main explanation which was suggested

for the observed effects deals with the fact that ILs can exist

as well-ordered hydrogen-bonded polymeric supramolecules

ꢂ

Lambda 25 spectrometer at 25 C.

Dynamic mechanical thermal analysis (DMTA) measurements

were carried out on films [typically length ꢀ width ꢀ thick-

ness ¼ 15 ꢀ 8 ꢀ 0.5 (mm)] with a Q800 model (TA Instru-

ments) operating in tension mode (strain between 0.05 and

nþ

nꢁ

ꢁ

2

of the type {[(K)

x

(X)xꢁn)] [(K)xꢁn(X)

x

)]

}

n

, where K is the

0

.07%, pretension: 10 N). Experiments are performed at 1

3

7,38

cation and X is the anion.

Thus, during the dilution pro-

ꢂ

Hz frequency and with a heating rate of 3 C/min from

cess ILs can break unfavorable methacrylate associates by

the construction of their own well-ordered hydrogen-bonded

polymer-type structures and accelerate photopolymerization

ꢂ

ꢁ

100 to þ 250 C. The set up provides the storage and loss

0

00

modules (E and E ) and the damping parameter or loss fac-

00

0

tor (Tan d) defined as the ratio Tan d ¼ E /E . The glass

2

6

of the latter. The nascent monomer/IL interactions may

lead to the formation of new associates (‘‘locally ordered

transition temperature (T ) of the polymers was determined

g

by thermomechanical method using a UIP-70 M (Russia)

thermomechanical analyzer at a heating rate of 2.5 C/min.

1

2

structures’’ ), which favor the polymerization.

ꢂ

Dynamic thermogravimetric analysis (TGA) was performed

In our continuous effort to investigate the viability of such

assumption and to study the photopolymerization process in

ILs, in this article we report the detailed study of photopoly-

merization of a series of methacrylate monomers in the pres-

ence of different ionic solvents. Polyethylene glycol dimetha-

in air on Q-1500 MOM derivatograph (Hungary) applying a

ꢂ

heating rate of 5 C/min. Mechanical properties (d —tensile

t

strength, E —tensile modulus, and e—elongation) of isotropic

t

polymer films were estimated using dynamometer ‘‘Polyani’’

(

Hungary). The both of strength d_C(MPa) and modulus E_C

crylates with consecutive increase of ACH ACH AOA units

2 2

(

Mpa) at uniaxial compression were measured by Dubov-

from 1 [PEGDM(1)] to 7/8 [PEGDM(7-8)] were specially cho-

sen as monomers (Scheme 2).

3

6

Regel apparatus with 0.0486 mm/min rate of compression.

Dielectric spectroscopy studies were run on a Novocontrol

Broadband Dielectric Spectrometer equipped with an Alpha

analyzer and a Quatro temperature controller. The films

were sandwiched between the gold-coated brass electrodes.

The experiments were carried out isothermally at each cho-

sen temperature. The conductivity was measured in the tem-

The molecules association in such a row must result not

only in the consecutive changes of bulk polymerization

kinetics but also in the appreciable changes of monomers

polymerization in the presence of added solvents. On the ba-

9

–11,26

sis of our previous studies

a range of different ILs was

taken (Scheme 2). This set of ionic solvents is covering most

important differences in ILs, namely, the nature of the cation

(aliphatic or aromatic), the length and isomerism of side alkyl

ꢂ

perature range from 20 to 50 C in 10 C step varying the

ꢁ

1

7

frequency from 10 to 10 Hz.

PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

SCHEME 2 Monomers, initiator and ionic liquids used in this study.

chains, the size of the anion [from small halogen anions to bulky

tris(pentafluoroethyl)trifluorophosphates] and the coordinating

ability of the anion (from strongly coordinated bromides to

weakly coordinated perfluorinated anions). To increase the

degree of molecules association, the PEGDMs polymerization was

carried out at room temperature by photochemical initiation.

the photolysis steps are practically coincided with each

other.

Thus, PQ photoreduction rate will directly influence the rate

of polymerization initiation reaction. Irradiation of the col-

ored PQ solutions in PEGDMs by UV and/or visible light

leads to their discoloration and polymerization of the mono-

mer. As a typical example, Figure 1 depicts changes in spec-

tral characteristics of the deaerated PQ solution in

PEGDM(1) upon its irradiation by light with k > 410 nm

during equal time domains.

Photoinitiation

9,10-Phenanthrene quinone (PQ) was chosen as photoinitia-

tor in the suggested study due to its effectiveness in poly-

merization process under the action of visible light. The irra-

diation by visible light was specially chosen to exclude the

overlapping of the monomers absorption spectra in the UV

region with the working absorption bands of the UV initia-

tors disintegrating according to the Norrish type I reaction.

Moreover, the use of the PQ, which is sensitive to visible

light, was essential because the investigated ILs can absorb

in various regions of the UV spectrum.

The reaction proceeds via the separation of a hydrogen atom

4

5

from hydrogen donor (HD) molecule by photo-excited PQ.

ꢄ

At this, two free radicals, namely PQH and D , are formed.

The latter initiates the radical polymerization process by

reaction with the monomer molecule M and formation of

new radical. For the monomers based on (meth)acrylates,

the role of hydrogen donor molecule can be effectively per-

4

6

formed by the ACH AOA monomer fragment :

2

PQ þ ꢁꢁCH2ꢁꢁO ꢁꢁ ! PQH^ꢄ

ꢅ

þ

ꢁꢁ CH ꢁꢁOꢁꢁ

ꢄ

FIGURE 1 Spectral changes of the PQ solutions in PEGDM(1)

under the irradiation by light with k > 410 nm during equal time

The generated carbon centered radical initiates the radical

polymerization of the PEGDM. Thus, the polymerization and

ꢂ

ꢁ3

domains (deaerated solution, T ¼ 25 C, [PQ] ¼ 2.5 ꢀ 10 M).

2392

INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE

FIGURE 2 (a) PQ disappearance kinetic curves during the irradiation by visible light of PQ solutions in: pure PEGDM(1), PEGDM(3),

PEGDM(4), and PEGDM(7-8) ([PQ] ¼ 1 ꢀ 10^ꢁ³mol/L, I ¼ 12 kLx, under vacuum); (b) PQ disappearance kinetic curves during the

3 2 5 3 2 2

irradiation by visible light of PQ solutions in: pure PEGDM(4) (1) and in mixtures PEGDM(4)/[1-CH -3-C H im](CF SO ) N (2),

29)]Cl (3) ([PQ] ¼ 1 ꢀ 10^ꢁmol/L, [monomer]:[IL] ¼ 9:1 by weight, I ¼ 12 kLx, under vacuum).

3

6 13 3

PEGDM(4)/[P(C H ) (C14H

It can be seen that the diminution of the PQ absorption

band in the 410 nm area is accompanied by simultaneous

increase of solution absorption band in the UV spectrum.

Moreover, the legible inflection is clearly observed (Fig. 1).

The presence of the isosbestic point testifies the conversion

of the PQ into the photoreduction products.

Bulk Photopolymerization

PEGDMs bulk photopolymerization kinetic curves are pre-

sented in Figure 3. PEGDM(1), PEGDM(2), and PEGDM(3)

photopolymerization curves (Fig. 3, curves 1–3) have charac-

teristic S-type nature. In contrast to that photopolymeriza-

tion curves of PEGDM(4) and PEGDM(7-8) posses two inflec-

4

7

tion points which is unusual for acrylic oligomers (Fig. 3,

curves 4 and 5).

The kinetic curves of PQ disappearance in pure monomers

solutions or in the solutions of monomers with added ILs

are shown in Figure 2.

In a similar manner, the dependences between the photopo-

lymerization reduced rate and the oligomer conversion are

also different (Fig. 4). PEGDM(1), PEGDM(2), and PEGDM(3)

curves have an extreme character (Fig. 4, curves 1–3), that

is, possess a certain maximum on the curve. Moreover, with

the consecutive increase in oxyethylene units in monomer

molecule from PEGDM(1) to PEGDM(3), the oligomers reac-

tivity increases.

It is clearly observed (Fig. 2) that the reaction of PQ photo-

reduction can be described by a kinetic equation of the

first order (d[PQ]/dt ¼ k

late the effective constants of PQ photoreduction rate (k

Table 1). The value of k_His consecutively increased with

H

ꢆ[PQ]). This allowed us to calcu-

H

)

(

the rise of the number of oxyethylene units in the range of

PEGDM(1)–PEGDM(3) (Table 1, entries 1–3). However, fur-

ther increase of the ACH ACH AOA groups quantity does

In such a way, the maximum polymerization reduced rate for

2

ꢁ

3

ꢁ1

not influence the k_Hvalue (Table 1, entries 3–5). Figure 2

also demonstrates photoreduction kinetics is not dependent

on the presence of any IL in the monomer solution. There-

fore, the photogeneration rate of initiating radicals in dime-

thacrylate medium is increasing from PEGDM(1) to

PEGDM(3) and is practically independent of the presence

of ILs additives.

PEGDM(1) was found to be W_m_a_x¼ 0.54 ꢀ 10

s , which

was observed at 15% of monomer conversion. At that, the

highest possible conversion for PEGDM(1) was equal to

H

TABLE 1 Effective Constants (k ) of PQ Photoreduction Rate

and the Calculated Values of the Intermolecular Interaction

Energy for PEGDM(n) Molecules [Eii(2)] and of the

Corresponding Ratio E (2)/E (1)

It is necessary to underline, that the polymerization of the

dimethacrylate monomers proceeds with the intermittent

increase of the viscosity and, respectively, with the loss of

fluidity even during the small conversion levels (1–3%).

Therefore, the termination reaction is limited by the diffu-

sion from the very beginning of the polymerization process.

Upon the formation of the crosslinked structure, the termina-

tion constant reduces markedly thus promoting the self-

excited acceleration of the polymerization. Similarly, the reac-

tivity of different dimethacrylate monomers is governed

mainly by the process of polymer chain growth and not by

ii

2

ꢁ1

)

No.

Monomer

k

H

ꢆ10 (s

E

ii(2) (kJ/mol)

Eii(2)/Eii(1)

1

2

3

4

5

PEGDM(1)

PEGDM(2)

PEGDM(3)

PEGDM(4)

PEGDM(7-8)

0.16

0.35

0.55

0.52

0.55

9.48

0.13

19.08

42.2

0.27

0.6

58.56

0.83

107.64/124.0

1.52/1.75

k

H

, effective constants of PQ photoreduction rate in PEGDM(n) medium;

ii(2), design value of intermolecular interaction energy for monomers

molecules; Eii(2)/Eii(1), ratio of the corresponding design values.

E

2

7,47

chain termination.

PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

monomers range. It was found that mentioned ILs do not

practically influence the kinetics of PEGDM(1) polymeriza-

tion [Fig. 5(a), curves 1–3]. In contrast, both ionic salts

equally increase the polymerization rate and conversion of

PEGDM(2) [Fig. 5(b), curves 1–3].

The action of ILs on the PEGDM(3) polymerization kinetics

is more selective. The addition of small quantities of [1-CH₃-

3

-C H im](CF SO ) N (<10 wt %) to PEGDM(3) does not

2 5 3 2 2

influence its polymerization. The increase of the IL’s concen-

tration to 30 wt % leads to the rise of PEGDM(3) polymer-

ꢁ

3

ꢁ1

ization reduced rate up to W_m_a_x/[M] ¼ 2.8 ꢀ 10

s

and

to the rise of the maximum conversion up to 90% [Fig. 5(c),

curves 1 and 2]. The influence of phosphonium IL is more

complicated. Its 10 wt % addition to PEGDM(3) increases

ꢁ

3

ꢁ1

polymerization reduced rate to 2.6 ꢀ 10

s

and mono-

mer conversion up to 80%. Further extension of tetradecyl-

trihexylphosphonium chloride concentration leads to the

decrease of polymerization reduced rate with the preserva-

tion of monomer conversion at 80% level [Fig. 5(c),

curve 3].

FIGURE 3 PEGDM(1)—1, PEGDM(2)—2, PEGDM(3)—3, PEGDM

(

4)—4, PEGDM(7-8)—5 bulk photopolymerization kinetic curves

[PQ] ¼ 1.1 ꢀ 10^ꢁmol/L, I ¼ 40 kLx).

2

The photopolymerization kinetics of PEGDM(4) and

PEGDM(7-8) is more sensitive to the addition of the men-

tioned ILs. Figure 5(d,e) demonstrate the suppression of

PEGDM(4) and PEGDM(7-8) photopolymerization by imida-

zolium IL. The decrease in both the reduced rate and the

maximum conversion is visually observed. Moreover, as men-

4

2%. Compare with PEGDM(2), the increase of both the

maximum polymerization reduced rate (W /[M] ¼ 1.40 ꢀ

max

ꢁ

3

ꢁ1

10

s

at 26% conversion) and the highest possible con-

version (up to 58%) was observed. For PEGDM(3), Wmax

/

ꢁ

3

ꢁ1

[M] ¼ 2.00 ꢀ 10

s

(at 31% conversion) and the maxi-

mum conversion equal to 73% was revealed. The described

increase in oligomers reactivity is in a full agreement with

^t^h^e^e^x^t^eⁿ^sⁱ^oⁿ^o^f^P^Q^kH and, as a sequence, with the exten-

sion of polymerization photogeneration rate. However, fur-

ther increase in oxyethylene fragments in monomer struc-

ture leads to the dramatic fall in monomer reactivity,

whereas photogeneration of free radicals became constant.

At that, qualitative changes in the polymerization reduced

rate/conversion dependence become apparent: starting from

PEGDM(4) two maxima are present [Fig. 4, curve 4]. The

first one is more intensive and is observed in the area of

26

tioned previously, the appearance of the photopolymeriza-

tion reduced rate/conversion dependence is changed with

the increase of [1-CH -3-C H im](CF SO ) N concentration.

3

2

5

3

2 2

The latter leads to the reduction of Wmax/[M] and to the dis-

appearance of the second maximum. The addition of tetraal-

kylphosphonium IL influences the PEGDM(4) and PEGDM(7-

8) polymerization oppositely to imidazolium one [Fig. 5(d),

curve 3 and Fig. 5(e), curve 3]. Thus, the presence of even

small quantities (2 wt %) of [P(C H ) (C H )]Cl results in

6

13 3 14 29

ꢁ

3

ꢁ1

small conversions (Wmax/[M] ¼ 0.44 ꢀ 10

s

at 11%

conversion), whereas the second small one is found at higher

ꢁ

3

ꢁ1

conversions (W_m_a_x/[M] ¼ 0.30 ꢀ 10

s

at 45% conver-

sion). The maximum possible conversion was equal to 68%.

The same behavior was observed for PEGDM(7-8) [Fig. 4,

curve 5]. It can be clearly seen that the increase of the

ethoxy groups number in the relevant monomers leads to

the consequent rise of their conversion from 42 for

PEGDM(1) up to 80% for PEGDM(7-8). The analogous effect

4

8

was previously observed by Anseth et al. during the inves-

tigation of the similar multiethylene glycol dimethacrylates.

Photopolymerization in Ionic Liquids

Influence of the Selected ILs Upon the PEGDM(n)

Photopolymerization Versus n

2

6

In continuation of our investigations,

-methyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)

imide ([1-CH -3-C H im](CF SO ) N) and tetradecyltrihexyl-

two ILs, namely

1

FIGURE 4 PEGDM(1)—1, PEGDM(2)—2, PEGDM(3)—3, PEGDM

3

2

5

3

2 2

(4)—4, PEGDM(7-8)—5 bulk photopolymerization reduced rate

ꢁ2

phosphonium chloride ([P(C H ) (C H )]Cl) were chosen

as additives for the photopolymerization of the presented

dependence versus monomer conversion ([PQ] ¼ 1.1 ꢀ 10 mol/

L, I ¼ 40 kLx).

6

13 3 14 29

2394

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ARTICLE

FIGURE

reduced rate as

monomer conversion

PEGDM(n) polymerization in bulk

1) and in the presence of X wt %

5 Photopolymerization

function of

for

a

(

3 2 5 3 2 2

of [1-CH -3-C H im](CF SO ) N (2)

6 13 3

or Y wt % of [P(C H ) (C14H29)]Cl

(

3). (a) n ¼ 1, X ¼ 10, Y ¼ 10; (b) n

2, X ¼ 10, Y ¼ 10; (c) n ¼ 3, X ¼

0, Y ¼ 30; (d) n ¼ 4, X ¼ 10, Y ¼ 2;

¼

3

(

e) n ¼ 7–8, X ¼ 10, Y ¼ 2 ([PQ] ¼

.1 ꢀ 10^ꢁmol/L, I ¼ 40 kLx).

2

1

four times increase of photopolymerization reduced rate. It

is necessary to mention that [P(C H ) (C H )]Cl changes

the first monomers group. The presence of the two rate max-

ima is typical only for PEGDM(4) and PEGDM(7-8). It can be

unambiguously stated that the mentioned fact is not due to

the presence of the oxygen traces in the photopolymerized

6

13 3 14 29

the character of the W_m_a_x/[M]—monomer conversion de-

pendence, which becomes typical as compared with

PEGDM(3). The increase in phosphonium salt concentration

results in the rise in photopolymerization reduced rate and

in monomer conversion (Fig. 6). The addition of 20 wt %

allows reach nearly quantitative conversion.

4

9

compositions like it was previously observed by Capek for

5

0

methyl methacrylate and by Soule for isobornyl methacry-

late, because the composition samples for kinetic studies of

all investigated monomers were prepared in the same condi-

tions (see vide supra), whereas the curves having two max-

ima were reproducibly observed only for PEGDM(4) and

PEGDM(7-8). Despite the rise in monomer viscosity from 9.3

for PEGDM(3) to 15.7 cP for PEGDM(4), the reactive ability

of the latter is significantly reduced. The viscosity of

PEGDM(7-8) is the highest (50 cP) among the investigated;

however, its reactivity remains as low as of PEGDM(4). Simi-

larly, both isolated monomer groups must differently

respond to the addition of the ILs. Obviously, studied ionic

The presented data clearly demonstrate that according to

their reactive ability in bulk and in solution photopolymeri-

zation, the used monomers can be divided into two groups:

PEGDM(1)–PEGDM(2)–PEGDM(3) and PEGDM(4)–PEGDM

(

7-8). The transfer from PEGDM(1) to PEGDM(3) is accom-

panied by four times increase in photopolymerization

reduced rate and simultaneously by commensurable increase

in photoinitiation rate (3.4 times increase in PQ photoreduc-

tion rate), which proves the invariability of reactive ability in

PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

2395

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

bear a side alkyl chain with different number of carbon

atoms, which can be either of isostructural or of linear struc-

ture. In particular, the imidazolium ILs can be symmetrical

or asymmetrical. Finally, the nature of the anions play an im-

portant role as well. According to the coordination ability,

anions can be either weakly or highly coordinated. The clas-

sical representatives of low coordinated anions are bis(tri-

fluoromethylsulfonyl)imides and bis(pentafluoroethylsulfonyl)

imides. In contrast, halogen-based anions are the highly coor-

dinated ones. Thus, for the photopolymerization of PEGDM(3)

and PEGDM(7-8), we tried to choose the representative from

each group and applied the optimum conditions elaborated

ꢁ

2

above ([PQ] ¼ 1.1 ꢀ 10 mol/L, I ¼ 40 kLx, [IL] ¼ 30 and 10

wt % for PEGDM(3) and PEGDM(7-8), respectively).

Taking into account that [1-CH -3-C H im](CF SO ) N accel-

3

2

5

3

2 2

erates PEGDM(3) photopolymerization, the influence of the

IL’s cation nature based on various bis(trifluoromethylsulfo-

nyl)imide ionic solvents was studied (Fig. 7). As it can be

seen (Fig. 7), all tested ILs increased the PEGDM(3) conver-

sion in comparison with its bulk photopolymerization. How-

ever, aliphatic-type ILs based on phosphonium and ammo-

nium cations decreased the PEGDM(3) photopolymerization

FIGURE 6 PEGDM(7-8) photopolymerization in the presence of

[

6 13 3

P(C H ) (C14H29)]Cl different amounts added: 0 (1), 2 (2), 10 (3),

₀₍₄₎_,_a_n_d₃₀₍₅₎_w_t_%₍_[_P_Q_]_¼₁_.₁_ꢀ₁₀_ꢁ2 mol/L, I ¼ 40 kLx).

2

1

2,25

salts increase the viscosity of monomer/IL solution.

ꢁ

3

ꢁ1

reduced rate from Wmax/[M] ¼ 1.96 ꢀ 10

s

to Wmax/

However, they only slightly influence the photopolymeriza-

tion of monomers from the first group and greatly change

the kinetics of those from the second. Therefore, the

obtained data on the monomers reactivity in the presence of

ILs can not be explained by the ordinary conception of

the viscosity influence upon the photopolymerization

ꢁ

3

ꢁ3 ꢁ1

[

M] ¼ 1.65 ꢀ 10 and 1.61 ꢀ 10

s , respectively. At

that both cyclic aliphatic and aromatic ILs increased photo-

polymerization reduced rate up to a maximum of 2.84 ꢀ

ꢁ

3

ꢁ1

10

s

in the presence of 30 wt % of morpholinium salt.

Interestingly that aromatic ILs based on the imidazolium and

pyridinium cations raised the monomer conversion up to

2

5,47

kinetics

like the presence of the viscosity synergism in

96–97%, whereas their alicyclic analogs allowed achieve the

monomer/solvent (ionic liquid) mixtures (i.e., the viscosity

of the mixture is higher than the simple additive combina-

tion of viscosities of the two components). To deeply under-

stand the type of the influence performed by ILs upon the

PEDGM(n) photopolymerization, the decision to enlarge the

set of ionic solvents was made. Two representatives of

the marked monomers groups, namely PEGDM(3) and

PEGDM(7-8), possessing various reactivity were chosen for

the subsequent photopolymerization in various ILs.

intermediate conversion between the photopolymerization in

aliphatic and aromatic-type ILs (Fig. 7).

Influence of ILs Nature Upon the PEGDM(3) and

PEGDM(7-8) Photopolymerization

3

,4,6,7

It is well known

that the properties of ILs depend on

the structure of the cation (the symmetry and the length of

alkyl substituents, the presence of hydrophobic groups, etc.)

as well as on the degree of anion charge delocalization. The

general problem in the use of ILs is the choice of the best IL

6

for a given process out of so far roughly 10 possible struc-

tural variations in the combination of different cations and

3

9–11,26,51–

anions. On the basis of our previous investigations

5

4

2,12,25,55

along with those reported by other groups,

it is

possible to divide commonly used ionic solvents into the

groups differing from each other by various factors. At first,

the nature of the cation can be aromatic, aliphatic, or alicy-

clic. The common representatives of aromatic ILs are pyri-

dinium-based and imidazolium-based ionic solvents, of ali-

phatic ILs are the ammonium and phosphonium ones, and of

alicyclic ILs -pyrrolidinium salts. Generally, each cation can

FIGURE 7 PEGDM(3) photopolymerization reduced rate depend-

ence upon the oligomer conversion in bulk and in tetradecyltri-

hexylphosphonium, tetradecyltrihexylammonium, N-methyl-N-

ethylpyrrolidinium, 1-methyl-3-ethylimidazolium, N-ethylpyridi-

nium, N-methyl-N-ethylmorpholinium bis(trifluoromethylsulfo-

nyl)imide ILs ([PQ] ¼ 1.1 ꢀ 10^ꢁmol/L, I ¼ 40 kLx, [IL] ¼ 30 wt %).

2

2396

INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE

C H im](CF SO ) N significantly better accelerates the reac-

4

9

3

2 2

tion giving practically quantitative polymer yield (Fig. 8).

For the investigation of how the anion’s nature influences

the PEGDM(3) photopolymerization, a set of ILs based on [1-

CH -3-C H im] cation and various anions was examined (Fig.

3

4 9

9). All the tested ILs were able to increase the PEGDM(3)

conversion in comparison with its bulk photopolymerization.

Only one IL, namely, 1-methyl-3-butylimidazolium tetrafluor-

oborate demonstrated the decrease in the photopolymeriza-

ꢁ

3

ꢁ1

tion reduced rate from Wmax/[M] ¼ 1.96 ꢀ 10

s

max

ꢁ

3

ꢁ1

10

s . The comparison of the influence of structurally

similar fluorinated anions revealed that phosphorous

containing hexafluorophosphate and tris(pentafluoroethyl)

trifluorophosphate ILs strongly accelerate PEGDM(3) photo-

polymerization than their hexafluoroantimonate or tetra-

fluoroborate analogs (Fig. 9). As it can be seen from Figure

FIGURE 8 PEGDM(3) photopolymerization reduced rate de-

pendence upon the oligomer conversion in bulk and in 1-

methyl-3-ethylimidazolium, 1-methyl-3-butylimidazolium, 1,3-

dibutyl imidazolium, 1-methyl-3-isobutylimidazolium, 1-methyl-

9, no correlation can be found between the size of the anion

and its influence upon the PEGDM(3) photopolymerization

reduced rate. The only evident conclusion that can be made

3

-hexylimidazolium, 1-methyl-3-tetradecylimidazolium bis(tri-

is that the ILs with organic anions better increase the W of

r

fluoromethylsulfonyl)imide ILs ([PQ] ¼ 1.1 ꢀ 10^ꢁ²mol/L, I ¼ 40

the PEGDM(3) photopolymerization, than ionic solvents

based on fully inorganic anions. At that, the highest

PEGDM(3) photopolymerization reduced rate equal to W_m_a_x/

kLx, [IL] ¼ 30 wt %).

Thus, ILs cations in accordance with their influence upon the

PEGDM(3) photopolymerization reduced rate can be placed

in the following order:

ꢁ

3

ꢁ1

[

M] ¼ 3.05 ꢀ 10

s

was achieved upon the use of [1-

CH -3-C H im]CF COO ionic salt (Fig. 9).

3

4

9

3

The final dependence of IL’s anion nature upon the PEGDM(3)

photopolymerization can be presented a following row:

ꢇ

CF3CO O > ðCF3SO2Þ N > P F6 > CF3SO3 >

At that the cation nature/PEGDM(3) conversion dependence

can be summarized as follows:

2

ꢇ

ðCF3CF2Þ P F3 > S bF6 > in bulk > B F4

3

Upon further investigation of how the cation’s nature influ-

ences, a set of imidazolium ILs differing in the alkyl chain

length having either asymmetrical or symmetrical structure

was synthesized. The realization of the PEGDM(3) photopoly-

merization process (Fig. 8) in the mentioned ILs resulted in

several conclusions. First, the photopolymerization is sensi-

tive to the length of the alkyl substitutes, namely, to the

hydrophobicity of ionic solvent. By the addition of the same

amounts of ILs, the photopolymerization reduced rate is rais-

ing with the increase of carbon atoms from 2 to 6 (Fig. 8)

ꢁ

3

ꢁ1

having its maximum at 3.02 ꢀ 10

s

in the presence of

[

1-CH -3-C H im](CF SO ) N, that is 1.6 times higher then

3

6

13

3

2 2

the polymerization reduced rate in bulk. However, subse-

quent increase of the alkyl chain length and the use of [1-

CH -3-C H im](CF SO ) N led to a small decrease of the

3

14 29

3

2 2

PEGDM(3) photopolymerization reduced rate (Fig. 8). The

change of the methyl substituent into the butyl one and the

FIGURE 9 PEGDM(3) photopolymerization reduced rate de-

pendence upon the oligomer conversion in bulk and in 1-

methyl-3-butylimidazolium tetrafluoroborate, hexafluorophos-

phate, hexafluoroantimonate, bis(trifluoromethylsulfonyl)imide,

trifluoromethanesulfonate, trifluoroacetate, tris(pentafluoroe-

thyl)trifluorophosphate ILs ([PQ] ¼ 1.1 ꢀ 10^ꢁmol/L, I ¼ 40 kLx,

[IL] ¼ 30 wt %).

use of symmetrical [1,3-(C H ) im](CF SO ) N salt resulted

4

9 2

3

2 2

r

in the decrease of W in comparison with asymmetrical [1-

CH -3-C H im](CF SO ) N analog. The comparison of the

3

4

9

3

2 2

2

influence of asymmetrical ILs with linear and isostructural

alkyl chains led to the conclusion that [1-CH -3-iso-

3

PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

2397

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

ILs could be placed according to their influence into the

order:

ꢇ

CF3SO3 > C l >ðCF3CF2Þ P F3 > B r >

3

ꢇ

P F6 > in bulk > ðCNÞ N > ðCF3SO2Þ N

2

Despite the evident advantage of the phosphonium ILs use

in the PEGDM(7-8) photopolymerization, the other ionic sol-

vents were also tested (Fig. 11).

Thus, a set of bis(trifluoromethylsulfonyl)imide ionic salts

bearing phosphonium, ammonium, pyrrolidinium, morpholi-

nium, and pyridinium cations were subjected for the exami-

nation. One can be astonished on the choice of the bis(tri-

fluoromethylsulfonyl)imide anion which demonstrated itself

in the combination with phosphonium cation as a reducing

additive for the PEGDM(7-8) photopolymerization reaction

(Fig. 10). However, this choice was performed due to the

reason, that bis(trifluoromethylsulfonyl)imide ILs possess

extremely good compatibility with methacrylate-based mono-

mers, and practically all of them are perfectly soluble in the

latter, that in its turn gave us the opportunity to compare

the influence of all the chosen cations. As it can be seen

from Figure 11, only one bis(trifluoromethylsulfonyl)imide

IL, namely, N-ethylpyridinium bis(trifluoromethylsulfonyl)-

imide, accelerates PEGDM(7-8) photopolymerization, where-

as the all others suppress it. However, it was possible to esti-

mate the influence of all chosen cations and to put them into

the following order:

FIGURE 10 PEGDM(7-8) photopolymerization reduced rate de-

pendence upon the oligomer conversion in bulk and in tetradecyl-

trihexylphosphonium tetrafluoroborate, hexafluorophosphate,

bromide, chloride, dicyanamide, bis(trifluoromethylsulfonyl)-

imide, trifluoromethanesulfonate, tris(pentafluoroethyl)trifluoro-

phosphate ILs ([PQ] ¼ 1.1 ꢀ 10^ꢁ²mol/L, I ¼ 40 kLx, [IL] ¼ 10 wt %).

As a consequence of the presented data, the prediction of

the best IL for the acceleration of PEGDM(3) photopolymeri-

zation reduced rate can be performed. Therefore, it seems

that exactly the N-methyl-N-isobutyl morpholinium trifluor-

oacetate ionic solvent could be the IL of choice. However, the

synthesis of such IL is rather complicated, that in its turn

limited us to the preparation of N-methyl-N-ethyl morpholi-

nium trifluoroacetate. Upon testing, the latter demonstrated

excellent acceleration of PEGDM(3) photopolymerization

ꢁ

3

ꢁ1

reduced rate with a maximum W equal to 2.81 ꢀ 10

s ,

r

thus proving our assumptions.

Upon switching to the investigation of ILs nature influence

on the PEGDM(7-8) photopolymerization, we took into the

consideration its superior acceleration by phosphonium ILs,

which was demonstrated above [Fig. 5(e)]. Thus, different

phosphonium ILs bearing [P(C H ) (C H )] cation and

6

13 3 14 29

various anions were synthesized and tested (Fig. 10). It was

revealed that the PEGDM(7-8) photopolymerization reduced

rate is greatly depended on the nature of the anion used.

According to Figure 10, the best acceleration occurred in the

presence of 10 wt % of corresponding trifluoromethanesul-

fonate IL, which allowed reaching the maximum of

PEGDM(7-8) photopolymerization reduced rate equal to

ꢁ

3

ꢁ1

W_m_a_x/[M] ¼ 2.69 ꢀ 10

s . At that, it was found that the

addition of the phosphonium ILs based on dicyanamide

and bis(trifluoromethylsulfonyl)imide anions reduced the

PEGDM(7-8) photopolymerization rate in comparison with

its bulk photopolymerization (Fig. 10). It is necessary to

FIGURE 11 Influence of the cation nature upon the PEGDM(7-8)

photopolymerization: bulk photopolymerization and in the presence

of 1-methyl-3-ethylimidazolium, tetradecyltrihexylphosphonium,

tetradecyltrihexylammonium, N-methyl-N-ethylpyrrolidinium, N-

ethylpyridinium, N-methyl-N-ethylmorpholinium bis(trifluorome-

thylsulfonyl)imide ILs ([PQ] ¼ 1.1 ꢀ 10^ꢁmol/L, I ¼ 40 kLx, [IL] ¼ 10

wt %).

3 3 3 2 3 3

mention that CF SO and (CF CF ) PF composed ionic salts

are changing the appearance of the PEGDM(7-8) photopoly-

merization curves in a similar manner as a chloride one (see

vide supra). Following the presented data all the examined

2

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INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE

2

6

Summarizing the previously obtained data and the data

presented in this article, it was possible to predict that the

best candidate for the acceleration of the PEGDM(7-8) photo-

polymerization needs to be based on the N-butylpyridinium

cation and trifluoromethanesulfonate anion. The use of the

mentioned IL resulted in PEGDM(7-8) photopolymerization

with 91% conversion and in excellent increase of the photo-

ꢁ

3

polymerization reduced rate up to W /[M] ¼ 2.26 ꢀ 10

max

ꢁ

1

s

, which is practically coinciding with best results obtained

for [P(C H ) (C H )]CF SO .

6

13 3 14 29

3

The turbidity was observed during the photopolymerization

of the following samples: PEGDM(3)/[N(C H ) ](CF SO ) N

6

13 4

3

2 2

(

30 wt %), PEGDM(3)/[1-CH -3-C H im]CF COO (30 wt %),

3 4 9 3

PEGDM(3)/[P(C H ) (C H )](CF SO ) N (30 wt %),

6

13 3

14 29

3

2 2

PEGDM(7-8)/[P(C H ) (C H )](CF SO ) N (10 wt %), PEGDM

6

13 3

14 29

3

2 2

(

7-8)/[P(C

H )

6 13 3

3 3

(C14H29)]CF SO (10 wt %), and PEGDM

(

7-8)/[P(C H ) (C H )](CN) N (10 wt %). However, the

FIGURE 12 Influence of the cation alkyl chains upon the

PEGDM(7-8) photopolymerization: bulk photopolymerization

and in the presence of tetradecyltrihexylammonium, ethyltrihex-

ylammonium, tetrabutylammonium bis(trifluoromethylsulfonyl)

imide ILs ([PQ] ¼ 1.1 ꢀ 10^ꢁ²mol/L, I ¼ 40 kLx, [IL] ¼ 2 wt %).

6

13 3

14 29

2

comparison of the kinetic data for the mentioned samples

and for the similar transparent ones revealed that their

kinetic curves are nearly identical.

One can propose the possibility of the halogen containing ILs

towards the photolysis with the subsequent formation of the

initiating radicals. To exclude such effect, the photoinitiation

was performed under the action of visible irradiation (see

vide supra). This was made due to the reason that in the

visible diapason, the investigated halogen containing ILs do

not absorb. In the same time, the acceleration of the photo-

polymerization is clearly seen upon the addition of ILs with

nonhalogen anions (Fig. 10). Moreover, the addition of

Interestingly, the impact of the studied bis(trifluoromethyl-

sulfonyl)imide ILs upon the corresponding monomer conver-

sion practically coincided with the cited order of their influ-

ence on the PEGDM(7-8) photopolymerization reduced rate

(

Fig. 11).

Finally, to ensure in the observed results several additional

experiments were carried out (Fig. 12). Three ammonium

bis(trifluoromethylsulfonyl)imide ILs with different alkyl

substitutes were tested in PEGDM(7-8) photopolymerization.

By performing these experiments, the influence of the two

factors was investigated; namely, the impact of the cation

symmetry and the length of the alkyl chain. Figure 12 clearly

demonstrates the advantage of the IL with longer alkyl sub-

stitutes. Thus, bis(trifluoromethylsulfonyl)imide ammonium

IL having tetradecyl side chain less suppresses the

PEGDM(7-8) photopolymerization than its analog with the

ethyl substitute. The addition of the symmetrical [N(C H ) ]

[

6 13 3

N(C H ) (C14H29)]Br does not lead to the change in the

photopolymerization rate of PEGDM(7-8) (Fig. 13). Finally,

the incorporation of [P(C H ) (C H )]Cl into the

PEGDM(1), PEGDM(2), or PEGDM(3) did not cause any

anomalous increase of their polymerization rate.

6

13 3 14 29

4

9 4

(

CF SO ) N] results in the decrease of the PEGDM(7-8) pho-

3 2 2

topolymerization reduced rate in comparison with the influ-

ence of [N(C H ) (C H )](CF SO ) N (Fig. 12).

6

13 3 14 29

3

2 2

To prove the fact that the established correlations are work-

ing independently on the anion nature, two pairs of structur-

ally similar ILs based on ammonium and phosphonium cati-

ons were compared (Fig. 13). As it can be seen, both

bromide ILs accelerate PEGDM(7-8) photopolymerization

with the increase of the reduced rate from W /[M] ¼ 0.62

max

ꢁ

3

ꢁ1

ꢁ3

ꢀ

10

s

to W_m_a_x/[M] ¼ 2.08 ꢀ 10 and 0.71 ꢀ 10

ꢁ

1

s

for [P(C H ) (C H )]Br and [N(C H ) (C H )]Br,

6 13 3 14 29 6 13 3 14 29

respectively. In contrast, both tested bis(trifluoromethylsulfo-

nyl)imide ILs suppressed the PEGDM(7-8) photopolymeriza-

tion (Fig. 13) with the preservation of the same distinction,

namely, ammonium IL more sharply depresses the investi-

gated photopolymerization.

FIGURE 13 Influence of the cation nature upon the PEGDM(7-8)

photopolymerization: bulk photopolymerization and in the pres-

ence of [N(C H ) (C₁₄H₂₉)]Br, [N(C H ) (C₁₄H₂₉)](CF SO ) N,

6

13 3

6

13 3

3

2 2

[P(C H ) (C₁₄H₂₉)]Br, and [P(C H ) (C₁₄H₂₉)](CF SO ) N ([PQ] ¼

6

13 3

6

13 3

3

2 2

1.1 ꢀ 10^ꢁmol/L, I ¼ 40 kLx, [IL] ¼ 10 wt %).

2

PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

2399

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

SCHEME 3 Schematic representation of the supposed ILs influence upon the PEGDM(n) photopolymerization.

The closer examination of the obtained results on the influ-

ence of the ILs addition upon the kinetics of PEGDM(n)

photopolymerization led us to the conclusion that it has a

very complicated character. At that, these data can not be

explained by the classical theory, like for example by the vis-

energy for PEGDM(n) molecules [Eii(2)]. The associates of

the first type are formed when E (2) is higher upon the

ii

association via methacrylic fragments. If the winning in

energy is higher at the intermolecular interaction of the oli-

gomeric units, then the associates of the second type are

prevailed. To a first approximation, the intermolecular inter-

action energy Eii(1) for the associates of the first type is a

2

5

cosity of the reaction media. Indeed, it was demonstrated

previously that the viscosity synergism is occurred in the

PEGDM(9)/IL mixtures (i.e., the viscosity of the mixture is

higher than the simple additive combination of viscosities of

constant. At the same time, the E (2) is dependent on the

ii

structure of the monomer oligomeric unit. Evidently, the

dimethacrylate monomer’s molecules will form the associ-

ates of the first type when the length of the oligomeric

spacer is minimal, that is, represents one ethylene fragment.

The consecutive increase of the spacer length by the intro-

duction of the ethoxy groups will lead to the situation when

E (2) > E (1). In its turn, this will result in the change of

2

5

the two components). However, it leaves unexplained the

fact that in some cases, the PEGDM(n) photopolymerization

kinetics was dramatically accelerated by the addition of only

2

wt % of the IL, which in its turn can not influence the vis-

cosity of the whole mixture. The obtained results do not also

correlate with the common physical–chemical properties of

ILs like density, polarity, the volume of the anion, etc. (Some

of the examples are listed in the Supporting Information.)

ii

the monomer molecules association type and in the respec-

tive change of the polymerization kinetics. Thus, it is possi-

ble to suppose that the notable decrease of the monomers

reactivity from PEGDM(3) to PEGDM(4) (Fig. 4, curves 3 and

4) is directly due to the change of the molecules association

type. The association of the PEGDM(4) molecules is occurred

mainly due to the interaction of the atoms of the neighbor

molecules oligomeric blocks. At that, the decrease in the

PEGDM(4) photopolymerization rate serves as an evidence

that such type of the molecules association is considered as

kinetically unfavorable in comparison with PEGDM(3).

One of the possible explanations could be connected with

the specific interactions between the PEGDMs and ILs

2

5

revealed by Andrzejewska et al. upon the investigation of

the FTIR spectra of the corresponding compounds and their

mixtures. When studied monomers are considered as associ-

ated liquids, the addition of the compound destroying or

reinforcing their association will greatly influence the

kinetics of their polymerization. In accordance with the

4

3

model of ‘‘kinetically favorable monomer associations,’’ the

monomer molecules are supposed to form relatively stable

associated structures, where the mutual orientation of the

molecules is directly depended on the structure of the oligo-

meric unit (Scheme 3). The realization of two types of pack-

If the molecules association is occurred owing to the interac-

tion of all atoms of both the methacrylic fragments and the

oligomeric spacers, then E (1) and E (2) can be calculated

ii

from the corresponding increments of the enthalpies of or-

4

3

37,43

ing is possible for PEGDMs. In the first type, the associa-

tion is mainly occurred between the atoms of the

methacrylate fragments of the neighbor monomer molecules,

whereas the second one is formed by the interaction of the

atoms in the elongated oligomeric parts of the close mole-

cules. The preferred realization of any type of the association

is determined by the value of the intermolecular interaction

ganic compounds evaporation.

According to the calcu-

lated values of the E (1) and E (2), it is possible to estimate

ii

the probability of the formation of a certain type association.

Table 1 depicts the design values of Eii(2) and the Eii(2)/

E (1) ratio. The E (1) was calculated for two methacrylic

ii

CH C(CH )C(O)OA fragments and was found to be 70.66 kJ/

2

3

mol.

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INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE

Despite the relative characteristic of the produced values,

they can quantitatively reflect the strengthening of the oligo-

meric unit role in the intermolecular interaction within the

increase of the spacer length (n) from PEGDM(1) to

PEGDM(7-8). Obviously, the transfer from the first type asso-

ciation to the association of the second type has to take

place when E (2)/E (1) will be equal to 1, that can be

will first break down into the layers along the alkyl–alkyl

border and, therefore, this decay will be easy. The resulting

ILs supramolecular structures will have on the border the

‘‘fringe’’ composed of the alkyl chains that can interact with

the monomer molecules, penetrating into the associates and

destroying them. As a result, the degree of the association

will be reduced and the polymerization rate will be

increased.

ii

clearly observed comparing the polymerization kinetics of

PEGDM(3) and PEGDM(4). Apart, it is well known that ILs

The mentioned approach to the explanation of the ILs nature

influence upon the PEGDM(n) polymerization is in good

agreement with the obtained experimental data (Figs. 5–13).

Let us consider the photopolymerization kinetics of

PEGDM(7-8) in the presence of the imidazolium salts having

different anions (Fig. 11 and ref. 26). The monomer polymer-

ization was suppressed by the addition of the bis(trifluoro-

methylsulfonyl)imide ILs (the highest reduced rate in bulk

3

7,38

are highly structured liquids.

The possible impact of IL

upon the monomer associates, namely, their destruction or

reinforcement, will be directly defined by the construction of

3

8,56,57

its supramolecular structures. It was demonstrated

that the mutual orientation of the ILs molecules in the solid

phase is characterized by the inner and intermolecular

hydrogen bonding between their cations and anions and is

maintained to a great extent in the liquid phase, that is, in

melts and solutions. The mentioned fact implies that the way

of influence of IL’s addition upon the PEGDM polymerization

kinetics could be determined to some extent from the infor-

mation obtained by X-ray studies of the ILs crystals struc-

ture. In other words, the information on the IL’s supramolec-

ular organization in the crystal allows extending this

knowledge to IL’s structure in the liquid state, thus predict-

ing possible interactions between the monomer and ionic

additive.

ꢁ

4

ꢁ1

was found to be W_m_a_x/[M] ¼ 6 ꢀ 10

s

in contrast to

obtained in the

presence of 10 wt % of the mentioned ILs) and accelerated

ꢁ

4

ꢁ4 ꢁ1

W_m_a_x/[M] ¼ 1.5 ꢀ 10 /3.8 ꢀ 10

s

ꢁ

4

ꢁ1

by the chloride IL (W_m_a_x/[M] ¼ 22 ꢀ 10

s

was detected

for the addition of only 2 wt % of [1-CH -3-C H im]Cl). At

3

4 9

the same time, the presence of both phosphonium and am-

monium bis(trifluoromethylsulfonyl)imide salts repressed

ꢁ

4

the PEGDM(7-8) polymerization (W /[M] ¼ 2.0 ꢀ 10

max

ꢁ

1

ꢁ4

s

for the phosphonium IL and Wmax/[M] ¼ 0.9/2.0 ꢀ 10

for the ammonium ones). Finally, the addition of the

5

6,58,59

According to the published data,

the quantity of the

phosphonium chloride IL led to the dramatical acceleration

cation–anion contacts as well as their strength are mainly

influenced by the anion nature. The more coordination cen-

ters has the anion, the more is the quantity of the hydrogen

bonds both inside the IL molecule and outside with the

other neighbor molecules. The strength of the physical net-

work built by the IL molecules is defined by the number of

hydrogen bonds and their length. ILs containing N, O, S, and

F atoms in the anion and acidic protons in the cation have

large amount of short hydrogen bonds that form strong

7,8

of the PEGDM polymerization reaching W_m_a_x/[M] ¼ 26/29

ꢁ4 ꢁ1

ꢀ

10

s .

3

The investigation of the PEGDM reactivity in the presence

of the various ILs (Figs. 5 and 7–9) revealed that the major-

ity of the tested ionic solvents accelerated the monomer pho-

topolymerization, however, demonstrating less effect on the

kinetics of the reaction in comparison with the influence on

7

,8

68

PEGDM. According to the X-ray studies, the triethylene

glycol disubstituted derivatives can possess two possible

4

–7,60,61

physical network.

The imidazolium salts bearing

configurations. The first one is ‘‘convolute.’’ It was found for

N(CF SO anion generate solid two-dimensional layered

3

2 2

)

0

the

crystallizable

2,2 -(1,2-phenylene-bis(oxy)diethanol)

supramolecular structures. For example, the lengths of the

hydrogen bonds in [1,3-(CH ) im](CF SO ) N are in the

dimethacrylate, which can serve as the structural analog of

PEGDM(3). The molecules in the studied crystal were packed

in stacks, and each molecule looked like an arc. The dis-

tances between the centers of the double bonds were found to

3

2

3

2 2

6

interval from 2.29 to 2.68 Å. In the contrast, the lengths of

the hydrogen bonds in similar ILs with halogen anions are

longer. Thus, in [1-CH -3-C H im]Cl, the lengths of the hydro-

3

4 9

6

8

6

3

be more than 4.3 Å. Such crystal can serve as a prototype of

the kinetically unfavorable associates. The second configura-

tion is ‘‘unfolded.’’ It was realized in the other structural analog

of PEGDM(3)—diquinone derivative of the triethylene glycol.

In molecule of the latter, the oxyethylene chain is elongated

gen bonds are equal to 2.57–2.932 Å, whereas in [1-CH -3-

C H im]Br correspond to 2.78–2.97 Å. The stronger are

3

6

4

2

5

the supramolecular structures of ILs, the lower is the proba-

bility of their disintegration in the monomer medium. Such

ILs structures will concentrate in the interassociative space

of the oligomer, contributing to an increase in the association

degree of the latter. Similarly, this should lead to the reduc-

tion of the observed monomer reactivity. The absence of the

acidic proton in ammonium and phosphonium salts

decreases the probability of the hydrogen bonds formation.

The molecules in the crystals of both the ammonium and

phosphonium salts having long side substitutes (more than

6

9

and lies in the plane. To conclude, it can be assumed that in

the liquid PEGDM(3) both of the two types of the molecules

association can take place. Thus, any of the chosen IL, by

affecting either the first type associates or the second type

ones, is predicted to accelerate the PEGDM(3) photopolymeri-

zation rate. This supposition was perfectly proved by the

obtained experimental data (Figs. 7–9).

4

–6 carbon atoms) form layers, with interdigitated alkyl

The described mechanism of interaction between the ionic

6

5–67

chains arrangement.

Upon their dissolution, such ILs

liquid additive and the chosen monomer is only

a

PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

2401

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

preliminary one. There is no any direct evidence of the sup-

posed ILs influence upon the monomer association. However,

the majority of the known traditional declarations such as

high viscosity of the system, etc., can not provide the con-

vincing explanation of the obtained results. In contrast, the

suggested theory of associates fit well the presented data

and is based on the experimental results, the analysis of X-

ray investigations, and the published literature. Therefore,

according to the referee’s recommendations, we leave it to

the reader’s decision whether to except it or not.

TABLE 2 Ionic Conductivity of Polymer Materials

[

3

1-CH -3-C

2 5

H im]

Conductivity

Polymer

Film

(CF SO

3

2

)

2

N IL

Plateau Value (rdc),

ꢂ

No.

Quantity (%)

[S/cm] at 25

C

a

1

2

3

4

5

6

7

8

9

PMMA

20

–

ꢁ11

PEGDM(3)

PEGDM(7-8)

–

4.42 ꢀ 10

ꢁ

8

6

4

20

50

70

85

–

9.59 ꢀ 10

5.09 ꢀ 10

2.03 ꢀ 10

3.55 ꢀ 10

2.96 ꢀ 10

6.30 ꢀ 10

3.87 ꢀ 10

6.17 ꢀ 10

3.62 ꢀ 10

6.08 ꢀ 10

Influence of ILs Upon the Properties of Obtained Polymers

As it was described previously (see vide supra) various poly-

mer processes were accomplished in ILs. The influence of

ionic solvents upon polymer formation process and the mo-

lecular weight of the resultant polymers was studied in

ꢁ4

ꢁ11

ꢁ

7

5

4

3

20

50

70

85

100

2

,5,70,71

1

0

detail.

However, only few examples could be found in

the literature describing physical–chemical properties of ILs/

polymer composites obtained via two possible methods. The

first one relates to the case when ILs are added to the pre-

liminary made polymers, for example, during films casting

process or by emerging of the corresponding polymers into

the ILs for swelling. The second consists in the conservation

of ILs inside the polymer structure after its synthesis in ionic

solvents. The discussed matter does not concern the specific

11

a

ꢁ3

12

a

For comparison.

will belong to those commercially available. Therefore, [1-

CH -3-C H im](CF SO ) N and [P(C H ) (C H )]Cl were

3

2

5

3

2 2

6 13 3 14 29

4

8,70,72–76

properties of polymer gels,

the question arisen is

selected as ionic additives satisfying the listed conditions for

photopolymerization of PEGDM(3) and PEGDM(7-8), respec-

tively. The latter were chosen as the representatives of the

two monomers groups that have been allocated in the previ-

ous part of this article due to the difference in their

reactivity.

about the comparison between the properties of common

polymers synthesized in traditional organic solvents and

their analogs obtained in or in the presence of ILs and, thus,

incorporating some amounts of ionic solvent after the syn-

thesis. In the latter case, the only information available is

7

7,78

dealing with the plasticization of PMMA

and polyvinyl-

7

9

chloride, alteration of porosity in the crosslinked poly-

Conductivity

5

75

mers, and modification of polymer thermal stability. At

the same time, purity problem of the synthesized polymers

after their isolation from reaction media, namely, ILs, was

It is well known that polymethylmethacrylate (PMMA), like

the majority of polymers, are dielectric materials. The same

relates to polymers derived from PEGDM(3) and PEGDM(7-

2

,5,51,55

repeatedly risen.

Ordinary, during the preparation of

8

). As it is seen from Table 2, both pure polymer films pos-

linear polymers in ILs it is possible to isolate them by com-

ꢁ11

sess conductivity equal to 10

S/cm (Table 2, entries 2

9

–11,51–54

mon precipitation process.

However, in the case of

and 7). However, based on the full compatibility of some

polymers with various ILs, the strategy consisting in the for-

crosslinked networks or of polymers that can interact with

ILs by means of ionic exchange or hydrogen bonding, even

the extraction in Soxhlet’s apparatus can result in the ILs

mulation of new composite materials by filling of the poly-

10,73,74,80,81

mer films with ILs was proposed.

nabe and coworkers

Moreover, Wata-

5

abandonment.

82,83

30,31

and MacFarlane et al.

suggested

In the present work, polymers were synthesized by photopo-

lymerization in the presence of ILs as catalytic additives.

Upon that, transparent solid materials were obtained, that

can either be washed of ILs or preserved as they were syn-

thesized thus incorporating some amounts of ILs inside.

Therefore, to understand the possible influence of ILs upon

the corresponding material’s properties, it seems reasonable

to investigate both pure polymer films and blocks and those

having residual ionic solvent. The choice of IL and its quan-

tity was made on the basis of the presented study (see vide

supra) and on the results obtained previously taking into

account several factors. At first, the chosen IL is subjected to

increase the monomer conversion to the highest possible

level. Second, the obtained polymer must be fully soluble in

the chosen IL. Finally, it would be preferred if the chosen ILs

new approach to the formation of electroconductive materi-

als via application of ILs both as reaction medium for radical

polymerization and as an end-type electrolyte, which

remains after the polymerization inside the gel-like material.

In the same way, several solid self-supported films based on

PEGDM(3) and PEGDM(7-8) incorporating different amounts

of [1-CH -3-C H im](CF SO ) N were synthesized and stud-

3

2

5

3

2 2

ied (Table 2). Interestingly, that for linear PMMA, the maxi-

mum quantity of IL, which can be inserted into the film until

it completely looses its mechanical stability and becomes

2

6

10

sticky, was previously found to be 60 wt %. In contrast to

that, the limit for the networks based on PEGDM(3) and on

more flexible PEGDM(7-8) is higher and equal to 85 wt %

(Table 2), whereupon with the rise of [1-CH -3-C H im]

3

2 5

(CF SO ) N quantity films get very sticky and completely

3

2 2

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INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE

curves 2 and 3). When IL amount is increased (curves 4 and

5), the overall spectra shift to higher frequencies so that the

conductivity increase is no longer observed in the experi-

mental frequency window. The shape of the conductivity

spectrum becomes similar to that of pure IL (Fig. 14, curve

6

). These changes in spectra are similar to those observed

8

4

for hydrated polymers where water acts as plasticizer,

reflects overall increase in the flexibility of polymer chains

and, hence, increases the mobility of target ions.

It was also of interest to compare PMMA, PEGDM(3), and

PEGDM(7-8)-based composites with equal amount of the

same IL (Fig. 15). As it was stated previously (e.g., as shown

in refs. 53,82,83,85–87), the lowering of polymer glass transi-

tion temperature can greatly improve the conductivity of the

resultant polymer material. In the same way, the presence of

3

oxyethylene fragments in polymers derived from PEGDM and

PEGDM(7-8) increases their flexibility, decreases glass transi-

tion temperature, and reduces the quantity of impediments

for the ions translational mobility in comparison with quite

rigid PMMA. As a result, PMMA-based composite demon-

strates the lowest conductivity, whereas material derived

from the most flexible PEGDM(7-8) reveals the highest (Table

2, entries 1, 3, and 8). The polarity of the polymer chain and

its compatibility with the chosen IL can certainly play an im-

portant role as well. Along with this, no dc conductivity can

ꢂ

FIGURE 14 Frequency dependence of the conductivity at 25

for [1-CH -3-C im](CF SO N (6) and for PEGDM(3)-based

networks incorporating 0 (1), 20 (2), 50 (3), 70 (4), and 85 (5) wt

of [1-CH -3-C im](CF SO N ionic liquid.

C

3

2

H

5

3

2 2

)

%

3

2

H

5

3

2 2

)

loose both the shape and the mechanical properties. As

expected, the conductivity of PEGDM(3)-based network was

increasing with the extension of IL quantity (Fig. 14) and

reached its maximum at 3.55 ꢀ 10 S/cm with 85 wt % of

IL inside (Table 2, entry 6). At that, the character of the con-

ductivity–frequency dependence curves is apparently differ-

ent (Fig. 14).

ꢁ

4

be detected for PMMA-based film with 20 wt % of [1-CH -3-

3

C H im](CF SO ) N IL (Fig. 15, curve 3), indicating that no

2

5

3

2 2

translational diffusion of ions is possible at the studied fre-

quencies and temperatures.

Usually, conductivity spectra of the disordered systems show

The increase of the ILs quantity in both the PEGDM(3) and

PEGDM(7-8)-based films resulted in the simultaneous

increase of their ionic conductivity. Thus, the highest conduc-

tivities were observed with the IL’s content equal to 85 wt %

0

plateau in r (giving the r , value of the conductivity in the

dc

dc limit, i.e., direct current conductivity) that is followed by

the conductivity dispersion. This part of spectra is character-

ized by the hopping mechanism of the charge carriers. The

critical point between the plateau and the subsequent con-

(

Table 2, entries 6 and 11). However, even in the latter case,

the conductivity of the composite films was lower than that of

ductivity extension, gives the value of the attempt rate x for

e

the charge carriers to overcome the highest energy level.

This parameter is usually considered to give an estimate of

the hopping rate of the ions and is known to be related to

the dc conductivity (x ꢈ r ). Thus, the higher is the value

e

dc

of the dc conductivity, the higher are the frequencies where

the plateau is observed. In addition to that behavior, conduc-

tivity decrease is often observed at low frequencies, which is

attributed to the electrode polarization effects. The molecu-

lar origin of such effect is the full or partial blocking of

charge carriers at the sample/electrode interface. This leads

to a separation of the positive and negative charges that

gives rise to an additional polarization. The characteristic

time constant of this process is proportional to the sample

thickness and inversely proportional to the dc-conductivity.

Thus, the effect is shifting to the higher frequency area with

the increase of the dc conductivity. In this work, Figure 14

clearly shows the difference in the conductivity behavior of

polymer materials incorporating inside various amounts of

IL. For the case of the 20 and 50 wt % addition, the conduc-

tivity spectra show both electrode polarization phenomena

and the response from the hopping conduction (Fig. 14,

ꢂ

FIGURE 15 Frequency dependence of the conductivity at 25

C

for PEGDM(7-8) (1), PEGDM(3) (2), and PMMA (3)-based films

containing 20 wt % of [1-CH

3

-3-C

2

H im](CF

5

3

SO

2

)

2

N ionic liquid.

PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

the sample is heated at a constant rate under a constant

load. The TMA method usually allows the determination of

all temperature intervals for the three mentioned polymer

physical states if they do exist. However, polymers based on

PEGDM(3) and PEGDM(7-8) represent crosslinked networks.

The TMA analysis of the pure PEGDM(3) film (Fig. 17, curve

1

) reveals that the curve’s bend takes place at the tempera-

tures higher than the temperature of polymer decomposition

Table 3, entry 5).

(

This can be explained by the fact that under the load, poly-

mer molecules due to the presence of flexible oxyethylene

fragments can compress until the state of the globules. After

the achievement of the ball like state, the polymer molecules

can not be pressed anymore and thermal decomposition

takes place, whereupon full stream of the decomposition

g

products is observed. Therefore, no T can be found out

from the TMA curve. Further incorporation of IL inside the

polymer leads to its swelling, that is, the molecules of cross-

linked polymer are slightly straightened. As a result, they

can be more compressed under the action of the same load

until the beginning of their decomposition (Fig. 17, curve 2).

The transfer to highly flexible PEGDM(7-8) results in the

reduction of the difference between the curves attributable

to pure polymer and to polymer with 10 wt % of

FIGURE 16 Frequency dependence of the conductivity for

PEGDM(3)-based network containing 85 wt % of [1-CH

3

-3-

C

2 5

H

im](CF SO N at various temperatures.

3

2 2

)

the corresponding [1-CH -3-C H im](CF SO ) N (Table 2,

3

2

5

3

2 2

entry 12). The PEGDM(7-8)-based film with 85 wt % of IL

revealed conductivity two times lower than pure IL and 10

times higher than film composed of PEGDM(3) polymer with

the same amount of IL. The difference between the PEGDM(3)

and PEGDM(7-8)-based polymers can be explained by two

factors. At first, by highest flexibility of PEGDM(7-8)-based

films. Second, by good compatibility of bis(trifluoromethylsul-

fonyl)imide ILs with polymer oxyethylene groups that are

more present in PEGDM(7-8) derived films.

[

P(C H ) (C H )]Cl (Fig. 17, curves 3 and 4). Nevertheless,

6 13 3 14 29

it can be concluded, that no glass transition temperature is

determined by TMA for synthesized polymer materials and

that the addition of ILs leads to the modification of polymer

blocks behavior under the constant load, namely to the

higher possible degree of their compression.

Another more sensitive and widespread method is the

DMTA, which studies temperature dependences of both real

and apparent parts of complex elasticity modulus as well as

It is known that the conductivity depends on the applied

temperature. In the case of PEGDM(3)-based network with

8

5 wt % of [1-CH -3-C H im](CF SO ) N, the increase of the

3 2 5 3 2 2

temperature leads to the noticeable change only in the ions

mobility. This results in the corresponding conductivity

increase, but with the full preservation of the curves shape

(

Fig. 16).

Thus, by temperature variations, it was possible to raise

ꢁ

4

ꢂ

films conductivity from 3.55 ꢀ 10 S/cm at 20 C up to

ꢁ

3

ꢂ

1

.45 ꢀ 10 S/cm at 50 C. More important was the fact

ꢂ

that upon cooling down the temperature to 20 C both the

value and the character of the conductivity were preserved

(

Fig. 16) that in its turn demonstrates the stable behavior of

the material obtained.

The same increase in approximately one order of magnitude

was observed for the conductivity of PEGDM(7-8)-based net-

work with 85 wt % of [1-CH

rising the experiment temperature up to 50 C.

3

-3-C

2

H

5

im](CF

3

SO

2

)

2

N upon

ꢂ

Mechanical Properties of Polymer Films

and Blocks Filled with ILs

Upon the determination of temperature intervals in which

polymer is found out in the solid (vitrified), high elastic

FIGURE 17 TMA of pure PEGDM(3) (1) film and PEGDM(3) net-

work filled with 50 wt % of [1-CH -3-C H im](CF SO ) N (2), as

3

2

5

3

2 2

(

rubberlike), or in the viscous-flow state, the thermomechan-

well as of pure PEGDM(7-8) (3) film and PEGDM(7-8) network

containing 10 wt % of [P(C 29)]Cl (4).

ical analysis (TMA) is frequently used. During such studies,

6 13 3

H ) (C14H

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ARTICLE

TABLE 3 Mechanical Properties of Various Pure Polymers and Materials Containing Ionic Liquids

Polymer Films

Polymer Blocks

Tensile

Compression

Strength

Compression

Modulus

a

IL Content

(wt %)

Strength

Elongation

Modulus

T

onset

b

ꢂ

No.

Monomer

d

t

(MPa)

e (%)

E

t

(MPa)

( C)

d

C

(MPa)

C

E (MPa)

1

2

3

4

5

6

7

8

9

a

PEGDM(7-8)

PEGDM(3)

–

14.5

4.0

28

73.2

36.6

–

170

200

240

165

220

235

250

255

20

97

c

2

12

20.3

57.7

65.7

c

10

–

11.7

d

20

–

3.0

13.5

1.5

11.5

13

15.4

890

255

14.9

10

–

15.1

11.5

11.2

3.5

30

842

d

20

50

70

85

–

12.4

53

d

12

–

d

0.5

18.5

4.4

–

c

IL ¼ [1-CH

3

-3-C

2 5

H im](CF

3

SO

2

)

2

N.

Phosphonium [P(C

Not determined.

6

H

13 3

) (C14

H

29)]Cl IL was used.

b

d

Onset loss temperature according to TGA.

of mechanical loss tangent. Figure 18 visually shows the loss

tangent (Tan d) as a function of temperature, which reveals

unusual behavior. At least three rather degraded peaks can

tioned above relaxations to the area of lower temperatures.

Moreover, the peaks height (Tan d_m_a_x) increases from 0.13 to

ꢂ

0.18 (at 127 and 76 C) and from 0.08 to 0.12 (at 25 and 7

ꢂ

be picked out at around þ130, þ20, and ꢁ10 C,

C), respectively. Such inward shifting and peak height exten-

respectively.

sion indicate the plasticizing effect of the chosen IL. Subse-

quent increase of IL quantity up to 50 wt % does not greatly

influence both the character of curve and the positions of

Tan d maxima (Fig. 18, curve 3). Figure 18 also indicates

that [1-CH -3-C H im](CF SO ) N is not able to crystallize

However, no slumps are observed on the corresponding tem-

perature dependence of the storage modulus (Fig. 19, curve

1). The modulus curve is slowly decreasing, thus no clear

3

2

5

3

2 2

transition temperature can be single out, which means that

all the mentioned relaxations are connected with the hetero-

geneity of the crosslinking in the studied network.

inside the polymer matrix hence the lowest relaxation is

ꢂ

observed at ꢁ62 C, temperature which is too low compared

ꢂ

32

to that of its melting point (ꢁ3 C). This can serve as an

additional evidence of the strong interaction between the IL

and the polymer matrix.

Apparently, the distribution of structures in PEGDM(3) film

is quite broadened, that is, along with the places of mesh

point’s concentration some various linear fragments are also

In contrast to PEGDM(3), the PEGDM(7-8) film demonstrates

rather typical for single networks behavior (Figs. 20 and 21).

presented. The addition of 20 wt

%

of [1-CH -3-

3

C H im](CF SO ) N (Fig. 18, curve 2) leads to the preserva-

2

5

3

2 2

ꢂ

Only one alpha relaxation peak is observed at þ11 C (Fig.

tion of the curve’s form and to the displacement of the men-

20, curve 1), whereas temperature dependence of the

FIGURE 19 Temperature dependence of the storage modulus

FIGURE 18 Tan d versus temperature for pure PEGDM(3) film

for pure PEGDM(3) film (1) and for PEGDM(3) films containing

(

[

1) and for PEGDM(3) films containing 20 (2) and 50 (3) wt % of

1-CH -3-C im](CF SO N according to DMTA analysis.

20 (2) and 50 (3) wt % of [1-CH

to DMTA analysis.

3

-3-C

2

H im](CF

5

3

SO

2

)

2

N according

3

H

2 5

3

2 2

)

PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

2405

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

vant films and transforms them into more elastic materials.

Finally, the insertion of 85 wt % leads practically to the elas-

tic material. In contrast to PEGDM(3), the PEGDM(7-8) rep-

resents itself as quite elastic material even despite its cross-

linked nature (Table 3, entry 1). Again, the addition of any of

the chosen ILs resulted in the plasticization of the films or in

the reduction of both the tensile strength and modulus (Ta-

ble 3, entries 2–4). It is noticeable that upon the addition of

only 2 wt % of the phosphonium IL, it is possible to achieve

double decrease in E (i.e., E is reduced by factor of 2) or

t

about four times reduction in d (Table 3, entry 2), which

t

indicates that greasy ILs with long side chains can act as

perfect softening agents.

FIGURE 20 Tan d versus temperature for pure PEGDM(7-8) film

(

1) and for PEGDM(7-8) films containing 20 wt % of [1-CH

im](CF SO (2), wt (3), and 20 wt (4) of

29)]Cl according to DMTA analysis.

3

-3-

During the compression test it was revealed that PEGDM(3)-

based polymer block represents solid with high compression

modulus equal to 842 MPa (Fig. 22, curve 1 and Table 3,

entry 5). The transfer to the forced elastic deformation area

appears as the curve inflection (Fig. 22, curve 1) from which

compression strength was calculated and found to be 30

MPa. The deformation in this area happens with small raise

in tension that is ordinary for solid materials.

C

2

H

5

3

2

)

2

N

2

%

[

6 13 3

P(C H ) (C14H

storage modulus depicts some secondary relaxations in the

range of 3100–2800 MPa (Fig. 21, curve 1).

Incorporation of the various amounts of [1-CH -3-

3

Incorporation of 50 wt % of imidazolium bis(trifluoromethyl-

sulfonyl)imide IL into the polymer block brings to the pro-

spective reduction of investigated parameters (Table 3, entry

C H im](CF SO ) N and [P(C H ) (C H )]Cl results in the

2

5

3

2 2

6 13 3 14 29

ꢂ

increase of T up to þ43 C (Fig. 20, curves 2–4) and respec-

a

tive shift of the relaxation peaks in the higher temperatures

region. At that, upon the addition of imidazolium IL, the

decrease from 0.34 to 0.31 is observed in Tan d peaks

height, whereas the presence of phosphonium IL increases

the corresponding Tan d maxima up to 0.45 (Fig. 20). Inter-

estingly that while the addition of 20 wt % and 2 wt % of

7) and simultaneously to the reduction of the curve’s slope

(

Fig. 22, curve 2). Thus, the insertion of IL into the

PEGDM(3)-based materials allows their softening and greas-

ing (lubrication), that in its turn helps to overcome their fra-

gility. In comparison with PEGDM(3), the PEGDM(7-8) sam-

ple has smaller compression modulus equal to 97 MPa

[

P(C H ) (C H )]Cl leads to the decrease of the storage

6 13 3 14 29

(

Table 3, entry 1) and behaves itself as a soft material in

modulus in comparison with pure PEGDM(7-8) film (Fig. 21,

curves 2 and 3), the incorporation of 20 wt % of [1-CH -3-

im](CF SO N results in the modulus increase (Fig. 21,

between the high elastic state and the glassy one (Fig. 22,

curve 3). Again, the incorporation of 10 wt % of IL leads to

the decrease of both the compression strength and modulus,

but this reduction is not so sensitive as for PEGDM(3) and

proceeds with the preservation of the curve’s shape (Fig. 22,

curves 3 and 4).

3

C

2

H

5

3

2 2

)

curve 4). Thus, in the case of PEGDM(7-8), it is possible to

conclude that ILs influence is rather complicated. The pres-

ence of IL brings not only to the plasticization of the result-

ant films, but also to the decrease of the distance between

the network nodes due to the additional physical interaction,

3

6

that is, to the increase of the ‘‘effective’’ network frequency.

This can also serve as an additional evidence of the specific

interaction between the PEGDM(7-8)-based polymer and

some of the ILs.

7

4,75

Because of the statement that ILs act as plasticizers

it

was of interest to investigate their influence on the polymer

materials both at tension and compression loads. The stretch

was performed on polymer films, while compression was

studied on polymer blocks. First, PEGDM(3)-based film was

quite brittle and allowed only 1.5% of elongation (Table 3,

entry 5). At that such film possessed high tensile strength

and modulus equal to 15.1 and 890 MPa, respectively. The

insertion of 20 wt % of bis(trifluoromethylsulfonyl)imide

imidazolium IL leads to the improvement of elasticity: the

maximum possible film’s elongation was increased up to

FIGURE 21 Temperature dependence of the storage modulus

for pure PEGDM(7-8) film (1) and for PEGDM(7-8) films contain-

ing 20 wt % of [1-CH -3-C H im](CF SO ) N (2), 2 wt % (3) and

11.5% (Table 3, entry 6); however, both the tensile strength

3

2

5

3

2 2

and modulus were reduced. The addition of 50 and 70 wt %

20 wt

6 13 3

% (4) of [P(C H ) (C₁₄H₂₉)]Cl according to DMTA

of the same IL even greater decreases d and E of the rele-

analysis.

t

2406

INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE

sion, which in its turn leaves some amount of monomer

inside the film and reduces its thermal stability. In contrast,

the addition of only 2 wt % of [P(C H ) (C H )]Cl into

6

13 3 14 29

ꢂ

the PEGDM(7-8) film increases its T in 30 C, whereas 10

wt % improve thermal stability on 70 C.

d

ꢂ

CONCLUSIONS

The photopolymerization of a set of poly(ethylene glycol)di-

methacrylates [PEGDM(n)] differ by the number of oxyethy-

lene units (n) in the presence of various ILs was investi-

gated. It was found that the studied monomers can be

divided into two groups: PEGDM(1)–PEGDM(2)–PEGDM(3)

and PEGDM(4)–PEGDM(7-8) in accordance with their reac-

tivity in the bulk and in solution photopolymerization. The

obtained results clearly indicate the influence of ILs nature

upon the photopolymerization kinetics of dimethacrylates is

rather complicated depending, probably, on several factors at

the same time. None of the common known properties of ILs

including the polarity, viscosity, the volume of the anion, etc.,

is able to separately describe or explain the established cor-

relations. The satisfactory answer could be given only by the

conception depicting in liquid monomers the presence of sta-

ble intermolecular structures with kinetically unfavorable

molecules arrangement. At that the influence of ionic liquid

addition upon the PEGDM(n) photopolymerization kinetics

consists in the changing of both the monomer and IL supra-

molecular structures. The destruction of the monomer asso-

ciates leads mainly to the acceleration of the corresponding

monomer polymerization. In contrast, the preservation of

IL’s supramolecular structure inside the monomer medium

could result either in the reinforcement of its kinetically

unfavorable association and as a consequence in the sup-

pression of its polymerization, or in the reinforcement of its

kinetically favorable association and in the slight acceleration

of the reaction.

FIGURE 22 Stress–strain curves of polymer blocks for pure

PEGDM(3) block (1), PEGDM(3) block containing 50 wt % of [1-

CH

3

-3-C

2

H

5

im](CF

3

SO

2

)

2

N (2), pure PEGDM(7-8) block (3), and

29)]Cl (4).

for PEGDM(7-8) block with 10 wt % of [P(C

6 13 3

H ) (C14H

Thermal Stability of Polymers Filled with ILs

Thermal stability as another valuable property of polymer

material is of great importance. Some of the known ILs pos-

sess rather high thermal stability, to be exact, the tempera-

ꢂ

tures of detectable degradation are equal to 220 C for

8

ꢂ

C

[

P(C H ) (C H )]Cl

and 320

for [1-CH -3-

3

6

13 3 14 29

C H im](CF SO ) N, respectively. Thus, it seems reasonable

2

5

3

2 2

to study the influence of ILs presence inside the obtained

polymer films on thermal behavior of the latter. It was

revealed that the addition of 20 wt % of bis(trifluoromethyl-

sulfonyl)imide imidazolium IL into the PEGDM(3) network

ꢂ

increases the T

Table 3, entries 5 and 6). Further extension of IL’s quantity

d

from 220 C for bulk PEGDM(3) to 235 C

It was demonstrated that ILs could be a design solvents

allowing the achievement of the maximum oligomer conver-

sion or the significant increase in the photopolymerization

rate. More interestingly, that upon carrying out of certain

experiments it is possible to predict the best IL structure for

the optimization of the concrete process.

(

to 85 wt % (Table 3, entries 7–9) resulted in the consistent

ꢂ

raise of thermal stability up to 255 C, which is found to be

in a full agreement with data published previously by Wata-

7

5

nabe and coworkers for PMMA/IL systems and by Winter-

5

ton and coworkers for various polymer/ILs composites.

7

5

However, in contrast to, no two-step weight loss process

was observed on TGA curves for PEGDM(3)/IL networks.

The TG curves show the degradation of PEGDM(3) films

incorporating inside any quantity of [1-Me-3-Etim]

Furthermore, it was found that the nature and the quantity

of the IL added strongly influences the properties of the

obtained polymer materials. The residual ionic solvents or

the specially added ones can physically interact with the

polymer networks thus increasing their thermal stability or

ambiguously changing their glass transition temperatures

(relaxation temperatures). ILs can plasticize the polymer net-

works making polymer films more flexible and decreasing

the fragility of the polymer blocks. This can serve the poten-

tial of ILs to be promising replacements for conventional

plasticizing agents. Polymer films based on PEGDM(7-8)

incorporating up to 85 wt % of corresponding IL demon-

(

CF SO ) N happens in one step, which can be attributed to

3 2 2

better compatibility (swelling) of PEGDM(3) networks with

IL, in comparison to linear PMMA, possibly due to their

crosslinked nature or to the presence of oxyethylene units.

Thermal behavior of PEGDM(7-8) materials was investigated

in the presence of both imidazolium and phosphonium ILs

(

Table 3, entries 1–4). The presence of 20 wt % of [1-CH -3-

3

C H im](CF SO ) N results conversely in the small decrease

2

5

3

2 2

ꢁ

3

of weight loss temperature in comparison with bulk

PEGDM(7-8) (Table 3, entries 1 and 4). This can be

explained by the fact that the aforementioned IL suppresses

PEGDM(7-8) photopolymerization and reduces its conver-

strated ionic conductivity equal up to 3.62 ꢀ 10 Sm/cm at

ꢂ

25 C. More important was the fact that the heating of the

ꢂ

composite films to 50 C and their subsequent cooling to 20

ꢂ

C resulted in the preservation of the conductivity curve

PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

2407

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA

shape that in its turn demonstrates the stable behavior of

the materials obtained.

18 Ryan, J.; Aldabbagh, F.; Zetterlund, P. B.; Yamada, B. Mac-

romol Rapid Commun 2004, 25, 930–934.

1

9 Perrier, S.; Davies, P. T.; Carmichael, A. J.; Haddleton, D. M.

This work was supported by Russian Foundation for Basic

Researches (Grants No. 08-03-01045_a, 09-03-00668_a, 09-03-

Eur Polym J 2003, 39, 417–422.

12286_ofi_m, 10-03-00391_a), French ECONET 2010-2012

20 Wu, G. Z.; Liu, Y. D.; Long, D. W. Macromol Rapid Commun

program (no. 23855UM) and grants provided by the President

of Russian Federation ‘‘For Scientific Schools’’ (Grant No. HIII-

2005, 26, 57–61.

2

1 Vijayaraghavan, R.; MacFarlane, D. R. Aust J Chem 2004,

7065.2010.3) and ‘‘For Young Outstanding Ph.D.’’ (Grant No.

5

7, 129–133.

MK-429.2009.3). Cytec (Cytec Canada Inc.) and, personally, Dr.

Allan Robertson are acknowledged for supplying phosphonium

ILs free of charge. Separate gratitude to Merck KGaA (Darm-

stadt, Germany) LSA R&D LSS S&TS Ionic Liquids Research

Laboratory and, personally, Dr. Nikolai Ignat’ev for the donation

of tri(pentafluoroethyl)trifluorophosphate containing ILs.

2

2 Zhou, H.; Jimenez, Z.; Pojman, J. A.; Paley, M. S.; Hoyle, C.

E. J Appl Polym Sci 2008, 108, 2509–2514.

23 Jimenez, Z.; Bounds, C.; Hoyle, C. E.; Lowe, A. B.; Zhou, H.; Poj-

man, J. A. J Polym Sci Part A Polym Chem 2007, 45, 3009–3021.

2

4 Andrzejewska, E.; St e˛ pniak, I. Polimery 2006, 51, 859–861.

5 Andrzejewska, E.; Podgorska-Golubska, M.; Stepniak, I.;

2

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PHOTOPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) DIMETHACRYLATES IN IONIC LIQUIDS, CHESNOKOV ET AL.

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Photopolymerization of Poly(ethylene glycol) dimethacrylates: The influence of ionic liquids on the formulation and the properties of the resultant polymer materials

DOI: 10.1002/pola.24008

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