Modification of styrene polymer with organosilicon groups

Article abstract of DOI:10.1002/hc.20314

The homopolymer of 4-chloromethylstyrene (PI) and its copolymers with styrene (in various mole ratios) were synthesized by bulk and solution free radical polymerizations, respectively, at 70±1°C using α,α′-azobis(isobutyronitrile) as an initiator. Lithiat

Full text of DOI:10.1002/hc.20314

Heteroatom Chemistry
Volume 18, Number 4, 2007
Modification of Styrene Polymer with
Organosilicon Groups
M. G. Assadi, M. Mahkam, and Z. Tajrezaiy
Chemistry Department, Azarbaijan University of Tarbiat Moallem, Tabriz, Iran
Received 24 July 2005; revised 2 July 2006
at low casts [2]. However, it also has some disad-
ABSTRACT: The homopolymer of 4-chloro-
methylstyrene (P1) and its copolymers with styrene
(in various mole ratios) were synthesized by bulk and
solution free radical polymerizations, respectively,
at 70 1◦C using α,αꢀ-azobis(isobutyronitrile) as an
initiator. Lithiation of these soluble polymers in THF
at −78◦C was done and reacted with electrophiles such
as tert-BuMe2Si, Et3Si, and Me3SiCH2 in the presence
of 4,4ꢀ-di-tert-butylbiphenyl (DTBB) as a catalyst
to produce modified polystyrene. In the other way,
trimethylsilylmethyl lithium substitute as a nucle-
ophile was covalently linked to the homopolymer and
copolymer. The polymers were characterized by IR,
1H NMR, 13C NMR, differential scanning calorimetry
(DSC), and gel permeation chromatography. DSC
showed that incorporation of silyl substitute in the
side chains of homopolymer and copolymers increases
the rigidity of the polymers and, subsequently, their
vantages. In order to overcome these disadvantages,
some works were done (for example, comonomers,
chain transfer agent, or cross-linking agents were
added to styrene polymer before it is polymerized)
[3]. Sometimes, saturated monomers were used for
reinforcement [4].
Chain transfer agents are used to regulate the
molecular weight, but they are rarely used in bulk
processes [5]. T-Dodecyl mercaptane is often used
as a chain transfer agent. To cross-link the styrene
polymer, divinylbenzene works very well, although
other cross-linking agents can also be used. Highly
cross-linked polymers can only be produced batch-
wise in bulk [6].
To improve the impact strength, polybutadiene
is generally added to polystyrene, in the amount
of 5–10% [1]. In order to improve the thermal
properties of polystyrene, poly-2,6-dimethyl-1,4-
phenyleneoxide (PPE) is added to the polymer. PPE
is a polymer with a glass transition temperature of
220◦C, and this polymer is miscible with polystyrene.
The addition of PPE to PS results in a polymer
blend with a higher glass transition temperature
than PS [7].
These copolymers found interesting application.
For example, copolymers with methacrylates are
used in manufacture of recording tapes and ton-
ers for photocopies. Other important work in this
area is attaching suitable groups as a side chain.
In this work, we synthesized silyl derivative of
polystyrene.
ꢁ
C
glass transition temperature. 2007 Wiley Periodicals,
Inc. Heteroatom Chem 18:414–420, 2007; Published on-
line in Wiley InterScience (www.interscience.wiley.com).
DOI 10.1002/hc.20314
INTRODUCTION
Polystyrene (PS) is one of the most important poly-
mers of today [1]. Its popularity stems from the
fact that it possesses many good properties, such
as good process ability, rigidity, transparency, low-
water absorbability, and that it can be produced
Attaching silyl groups to polymer chain is an
interesting research field in polymer and silicon
chemistry. In this way some important polymer
Correspondence to: M. G. Assadi; e-mail: mgalehassadi@
yahoo.com, mg-assadi@azaruniv.edu.
2007 Wiley Periodicals, Inc.
c
ꢀ
414

Modification of Styrene Polymer with Organosilicon Groups 415
properties, such as permeability and gas
permeability parameters, and mechanical, ther-
mal, and surface properties are modified. For
example, various organosilyl groups were bounded
to a number of polymers and their properties were
studied [8–12]. 4-Chloromethylstyrene (CMS), also
called p-vinyl benzyl chloride (VBC), is a monomer
that can be reacted with a series of reagents to pro-
duce polymer with functional groups [13,14]. This
monomer can polymerize or copolymerize before
or after the functional groups reaction with benzyl
chloride. The mobility of benzyl chloride bonds
in poly(4-chloromethylstyren) (PMS) and related
copolymers allows their reaction with various nu-
cleophilic reagents. Also functionalized PCMS and
related copolymers have been widely used in dif-
ferent processes such as bactericide polymers [15],
photosensitizers [16], solar energy storage [17], pho-
toresist [18], nonlinear optics [19], and prodrugs in
biochemical application [20].
molecular weights (MW and Mn) were determined
using a waters 501-gel permeation chromatograph
(GPC) fitted with 102 and 103 nm waters styragel
columns. THF was used as an elution solvent at a
flow rate of 1 mL/min, and polystyrene standard was
employed for calibration. The glass transition tem-
perature was determined with a Perkin-Elmer DSC
differential scanning calorimeter at a heating rate of
10◦C/min in air.
Materials
Solvents such as Dioxan (Merck) and THF (Merck)
were dried by standard methods. Et3SiCl, t-
BuMe2SiCl, Ph3SiCl, Me3SiCH2Cl, and Li powder
were used as received. 4-Chloromethylstyrene and
styrene were distilled under reduced pressure to re-
move inhibitors, before use. The initiator of α,αꢀ-
azobis (isobutyronitril) (Merck) was purified by crys-
tallization from methanol.
One of the modifications of PCMS and related
copolymers is achieved by nucleophilic substitu-
tions of the chlorine atom, with the steric hin-
drance nucleophile, i.e., tris(trimethylsilyl) methyl
anion [21]. Also a series of soluble polymers
that have linear character metallated and re-
acted with some electrophilic reagents [22–24];
for example, lithiation of soluble polymer such as
pol(4-chloromethylstyrene) was done and reacted
with electrophiles in the presence of 4-4-di-tert-
butylbiphenyl (DTBB) as a catalyst using or not us-
ing Barbier-type reaction conditions at –78◦C, to
produce polymer with a silyl group in a polymer
chain [14].
In the literature, there are already examples of
some interest in this area. Among those were car-
bosilanes with Me3SiCH2substituents [25], substi-
tuted poly(acetylenes) such as poly(1-trimethylsilyl-
1-propyne) [26], or its alkylated analogous [27].
In this way, we first synthesized the homopoly-
mer of 4-chloromethyl styrene and its copolymer
with styrene by radical polymerization. Then some
silyl groups were attached to the resulting poly-
mers. Then these polymers with an organosili-
con chain were characterized and studied for their
properties.
Homopolymerization of 4-Chloromethylstyrene
In a quickfit pyrex polymerization tube, 1% molar of
1,1ꢀ-azobis (isobutyronitrile) (AIBN) as an initiator
was dissolved in 10 mmol of CMS and the solution
was flushed gently with argon for about 20 min. Then
the solution was shaken vigorously in a thermostatic
water bath at 70 1◦C by a shaker machine under
argon for 48 h. After this, the resulted solid was dis-
solved in 20 mL THF and poured into 150 mL of
cooled methanol as nonsolvent. Then the obtained
white precipitate was washed with methanol and
dried in vacuum at room temperature to give P1 (1 g)
(Scheme 1).
1H NMR (CDCl3, ppm): 1–1.8 (CH2 CH), 4.5
(CH2 Cl), 6.5–7.3 (Ar CH3).
FT-IR (KBr, cm–1): 3050 (aromatic, C H), 2910,
2850 (aliphatic, C H), 1420, 1611 (aromatic,
C C).
EXPERIMENTAL
Measurements
Infrared spectra were recorded with a 4600 Uni-
cam FT-IR spectrophotometer as KBr pells. 1H NMR
spectra were run on a Bruker 400 MHz spectrometer
at room temperature using CDCl3 as a solvent. The
SCHEME 1 Preparation of P1 and modified homopolymers.
Heteroatom Chemistry DOI 10.1002/hc

416 Assadi, Mahkam, and Tajrezaiy
into cold methanol and the resulting precipitate was
filtered, and was washed several times with cold
methanol to produce pure compounds. Preparation
of P1, I, II, and III–VII is shown in Schemes 1 and 2,
respectively.
Copolymerization of 4-Chloromethylstyrene
with Styrene
For preparing of copolymers (P2, P3, and P4), a mix-
ture of styrene (150 mmol) with different amounts of
4-chloromethylstyrene (30, 150, and 50 mmol) with
molar ratios of 5:1, 1:1, and 3:1, respectively, was
dissolved in 15 mL of dioxan and was mixed with
1,1ꢀ-azobis(isobutyronitrile) (AIBN) (1% molar) as
a radical initiator, in a pyrex glass ampoule. The
ampoule was degassed, sealed under vacuum, and
For I: 1H NMR (CDCl3, ppm): 0.55 (CH2 Si),
0.85 (CH3 ), 1.2–1.9 (CH2 CH), 6.6–7.0(Ar H), 3.0
(CH2 Ar). FT-IR (KBr, cm–1): 3016 (aromatic C H),
2957 (aliphatic C H), 1456 and 1610 (aromatic
C C), 1261 (C Si).
1
For II: H NMR (CDCl3, ppm): 0.09 (CH3 Si),
maintained at 70
1◦C in a water bath, with stir-
0.9 (t-Bu), 3.0 (CH2 Ar), 1.2–1.9 (CH2 CH), 7.0–7.4
(Ar H). FT-IR (KBr, cm–1): 3023 (aromatic C H),
2923 (aliphatic C H), 443, 1611 (aromatic C C),
1264 (C Si).
ring for about 72 h. Then the solutions were poured
from ampoules into cooled methanol. The precipi-
tates were collected and washed with methanol and
dried under vacuum to give copolymers (P2, P3, and
P4) (Scheme 2).
1
For III: H NMR (CDCl3, ppm): 0.5 (CH2 Si),
0.9 (CH3 ), 1.1–2.1 (CH2 CH), 3.0 (CH2 Ar),
4.5 (CH2Cl), 6.6–7.2 (Ar H).FT-IR (KBr, cm–1):
3060 (aromatic C H), 2848–2923 (aliphatic
C H), 1452 and 1600 (aromatic C C), 1263
(C Si).
1H NMR (CDCl3, ppm) for P2, P3, and P4: 1–1.8
(CH2 CH), 4.5(CH2 Cl), 6.4–7.2 (Ar CH3).
FT-IR (KBr, cm–1): 3027 (aromatic C H), 2925,
2850 (aliphatic C H), 1451–1600 (aromatic C C).
For IV: 1H NMR (CDCl3, ppm): 0.1 (CH3 Si), 0.9
(t-Bu), 1.1–2.0 (CH2 CH), 3.7 (CH2 Ar), 4.5 (CH2Cl),
6.6–7.2 (Ar H). FT-IR (KBr, cm–1): 3027 (aromatic
C H), 2925 (aliphatic C H), 1494 and 1610 (aro-
matic C C), 1263 (C Si).
General Procedure for the Preparation of
Modified Polymers (Compounds I–VII)
For V: 1H NMR (CDCl3, ppm): 0.1 (CH3 Si), 1.0–
2.3 (CH2 CH), 3.4 (CH2 Ar), 4.5 (CH2Cl), 6.1–7.1
(Ar H). FT-IR (KBr, cm–1): 3025 (aromatic C H),
2924 (aliphatic C H), 1452 and 1601 (aromatic
C C), 1265 (C Si).
To a dark green suspension of lithium powder
(12 mmol) and DTBB as a catalyst (10% molar) in
dry THF (25 mL ), a solution of the copolymers
(P2, P3, and P4) (1 mmol), or homopolymer (P1)
(1 mmol), with related electrophiles (1.5 mmol) in
THF, was slowly added from a dropping funnel un-
der argon at –78◦C. After stirring for about 7 h at the
same temperature, the resulting mixture was poured
1
For VI: H NMR (CDCl3, ppm): 0.65 (CH2 Si),
0.98 (CH3), 1.20–2.50 (CH2 CH), 2.78 (Ar CH2),
6.60–7.26 (Ar C H). FT-IR (KBr, cm–1): 1265 and
SCHEME 2 Preparation of P2 and modified copolymers (III, IV, VI, and VII).
Heteroatom Chemistry DOI 10.1002/hc

Modification of Styrene Polymer with Organosilicon Groups 417
7.5 (Ar, C H). FT-IR (KBr, cm–1): 3027 (aromatic
C H), 2925 (aliphatic C H), 1494 and 1610 (aro-
matic C C), 1262 (C Si).
1
For IX: H NMR (CDCl3, ppm): 0.09 (CH3 Si),
1.1–1.9 (CH2 CH), 2.2 (CH2 Ar), 4.5 (CH2Cl), 6.6–
7.2 (Ar H). FT-IR (KBr, cm–1): 3027 (aromatic
C H), 2925 (aliphatic C H), 1494 and 1610 (aro-
matic C C), 1263 (C Si).
SCHEME 3 Preparation of trimethylsilylmethyllithium and
attaching it to P1, (VIII), and P2, (IX).
RESULTS AND DISCUSSION
823 (C Si), 1492 and 1601 (C C), 2923 (aliphatic
C H), 3025 (Ar C H).
The monomer of CMS was homopolymerized and
copolymerized with styrene with ratios of [1:1], [1:3],
For VII: 0.48–0.53 (SiCH3), 0.89–1.00 (t Bu),
1.04–2.30 (CH2 CH ), 2.79–3.02 (Ar CH2), 6.60–
7.26 (Ar C H). FT-IR (KBr, cm–1): 1265, 825 (C Si),
493, 1602(C C), 2923 (aliphatic C H), 3025 (Ar,
C H).
[1:5] at 70
1◦C using AIBN as the radical ini-
tiator to produce P2, P3, and P4, respectively. The
reaction conditions are shown in Table 1. The re-
sulting polymers and copolymers are white solids
and soluble in chloroform, dichloromethane, ben-
zene, toluene, xylene, THF, N,N-dimethylformamid,
and dimethylsulfoxide but insoluble in n-hexane,
methanol, ethanol, and water.
Organolithium Method for Preparation of
Modified Polymers (Compounds VIII–IX)
Trimethylsilylmethyllithium was prepared by re-
action of chloromethyltrimethylsilane and lithium
metal powder suspension in the dry heptane. The
halide solution was added dropwise at room tem-
perature over a 1 h period to a suspension of lithium
powder in about 1.5-fold excess with stirring. The
system was heated with stirring at 55–60◦C for 5 h,
and then lithium chloride and excess lithium were
filtered on a frit, the solvent stripped off in vacuum.
The solid was dissolved in THF and added dropwise
from an ampoule into a flask that includes poly-
mer solution in THF under argon. Then the mixture
was refluxed over 5–6 h and poured into the cold
methanol; the residue was filtered and washed with
methanol (Scheme 3).
Copolymers (P2, P3, and P4) and homopoly-
mer (P1) compositions were determined using H
1
NMR spectroscopy. The molar compositions of P1,
P2, P3, and P4 are presented in Table 2. Increas-
ing the reaction time in homopolymerization in
bulk referred to in solution causes high MW and
Tg in polymers. In copolymers of P3, P4 with ra-
tios of [1:3] and [1:1], respectively, incorporation
of the silyl group in the side chain of polymer
was done better refer to copolymer with a ratio of
1:5, where the peak of CH2Cl in 1H NMR disap-
peared. This means that all of CH2Cl groups were
substituted by silyl groups. This can be referred
to reducing hindrance in copolymers. In this case,
we attached tert-butyldimethylsilyl and triethylsilyl
groups to these copolymers with good yield. After
preparation of homopolymer and copolymers, each
For VIII: 1H NMR (CDCl3, ppm): 0.09 (CH3 Si),
1.2–1.9 (CH2 CH), 2.8 (CH2 Ar), 4.5 (CH2Cl), 6.4–
TABLE 1 Preparation Conditions of Homopolymer and Copolymer at 70 1◦C
Sample
Monomer 1
Monomer 2
Ratio of 1
Ratio of 2
Solvent
Time (h)
T (◦C)
Nonsolvent
P1
P2
P3
P4
CMS
CMS
CMS
CMS
–
1
1
1
1
–
5
3
1
–
72
72
72
72
70 1◦C
70 1◦C
70 1◦C
70 1◦C
MeOH
MeOH
MeOH
MeOH
Styrene
Styrene
Styrene
Dioxan
Dioxan
Dioxan
TABLE 2 Composition and Molecular Weights of P1, P2, P3, and P4
Sample
Mol % CMS
Mol % Styrene
Tg ( ◦C)
Mn
Mw
Mn/Mw
P1
P2
P3
P4
100
16.7
25
–
83.3
75
80
73
73
79
41,059
22,344
26,122.25
35,373.8
32,441
5,923
1,6225
1,6079
1.26
3.76
1.61
2.20
50
50
Heteroatom Chemistry DOI 10.1002/hc

418 Assadi, Mahkam, and Tajrezaiy
of them was lithiated with lithium powder in the
presence of DTBB at −78◦C and reacted with
organosilicon electrophiles to produce modified ho-
mopolymers (Scheme 1) and modified copolymers
(Scheme 2) with a silyl side chain. The triethylsilyl,
tert-butyldimethylsilyl, trimethylsilyl methyl groups
were used as a silyl side chain groups in these copoly-
mers and homopolymer. In this way, we prepared
some new silyl derivatives of polystyrene. In this
case, the best result was obtained under Barbier-
type conditions, performing the final hydrolysis with
cold methanol. Thus, functionalized polymers I–VII
were isolated. Either for the two-step or for the Bar-
bier process, a chlorine–lithium exchange occurred
prior to the reaction with the electrophile, so the
corresponding benzylic organolithium intermediate
is probably involved in the reaction.
Preparation of modified polymers was done by
the other method, in which chloromethyltrimethyl-
silane lithiated by lithium powder in heptane at
60◦C then solvent evaporated, and the resultant com-
pound was reacted with P1 and P2 to produce VIII
and IX (Scheme 3). By DSC analyses, the effect of
silyl groups in properties of poly(CMS) was studied.
These studies showed that attaching a silyl group
caused modification of polystyrene. Tg values and re-
action conditions of compounds I–VII and VIII–IX
are shown in Tables 3 and 4, respectively.
copolymer; for example, attaching triethylsilyl and
tert-butyldimethylsilyl groups to homopolymer (P1)
and copolymers (P3, P4) was done in near 100%
1
yield, where the H NMR peak of (CH2-Cl) group
1
disappeared; the H NMR spectrum of compound
I is shown in Fig. 1. Because in the case of ho-
mopolymer, the steric hindrance was reduced re-
ferred to copolymer; therefore, attaching the elec-
trophiles was done better. For example, attaching
the triethylsilyl or tert-butyldimethylsilyl groups to
copolymer (P2) was done in low yield referred to
homopolymer. In copolymers P3, P4 the mole per-
centage of chloromethystyrene is higher than that in
P2; the yield is suitable. The spectrum of compound
IV is shown in Fig. 2.
Identification of silyl derivative that was pre-
pared from organolithium reaction was also done
by a spectroscopic method; for example, a typical
1H NMR spectrum of Me3SiCH2 derivative of P1 is
shown in Fig. 3. 1H NMR data of polymers are shown
in Table 5.
The thermal behavior of polymer is important
in relation to its properties. Differential scanning
calorimetry (DSC) and thermal gravimetry (TGA)
for the network polymers were evaluated. We deter-
mined glass transition temperature (Tg) of all mod-
ified polymers by the DSC analyses. Tg values of
homopolymers and copolymers showed that the
presence of the silyl group in the side chain in-
creased the rigidity of polymers, and the Tg value
subsequently increased. On the other hand, it ap-
peared that in these series of polymers with in-
creased hindrance in silyl groups, with the decrease
of the chains flexibility, the Tg values increased. The
Tg values in homopolymer are higher than those in
Replacement of chlorine atoms by Si elec-
trophiles is determined by 1H NMR, where the peak
around 4.6 ppm corresponding to two methylene
protons of benzyl chloride in CMS disappeared or
reduced integral of peak and two new peaks ap-
peared. In the case of homopolymer, the yield of
incorporation of the silyl group is better referred to
TABLE 3 Reaction Conditions and Tg Values of Modified Polymers
Modified Polymers
Electrophiles
Related Polymer
Solvent
Time (h)
Tg (◦C)
Reaction Conditions
a
I
Triethylsilyl
tert-Butyldimethylsilyl
Triethylsilyl
tert-Butyldimethylsilyl
Methyltrimethylsilyl
Triethylsilyl
P1
P1
P2
P2
P2
P3
P4
THF
THF
THF
THF
THF
THF
THF
7
7
7
7
7
7
7
98
–
–
–
–
–
–
–
a
II
111
104
104
103
105
112
a
III
IV
V
VI
VII
a
a
a
a
tert-Butyldimethylsilyl
aThese reactions were performed under the Barbier-type condition in the presence of DTBB, and methanol was used as a nonsolvent.
TABLE 4 Reaction Conditions and Tg Values for Modified Polymers (VIII–IX)
Sample
Nucleophile
Electrophile
Solvent
Nonsolvent
Time (h)
Tg (◦C)
Reaction Conditions
a
VIII
IX
Me3SiCH2Li
Me3SiCH2Li
P1
P2
THF
THF
Methanol
Methanol
2
2
108
103
–
–
a
aThese reactions were performed by an organolithium reagent with electrophiles.
Heteroatom Chemistry DOI 10.1002/hc

Modification of Styrene Polymer with Organosilicon Groups 419
FIGURE 1 1H NMR spectrum of (P1-Et3Si) (I).
FIGURE 2 1H NMR spectrum of (P2-t-BuMe2Si) (IV).
TABLE 5 1H NMR Data of Polymers
Polymers
δ(ppm) in CD3Cl
I
II
0.55 (CH2 Si), 0.85 (CH3 ), 1.2 –1.9 (CH2 CH), 6.6–7 (Ar H), 3 (CH2 Ar).
0.09 (CH3 Si), 0.9 (t-Bu), 3 (CH2 Ar), 1.2–1.9 (CH2 CH), 7–7.4 (Ar H).
III
IV
V
VI
VII
VIII
IX
0.5 (CH2 Si), 0.9 (CH3 ), 1.1–2.1 (CH2 CH), 3 (CH2 Ar), 4.5 (CH2Cl), 6.6–7.2 (Ar H).
0.1 (CH3 Si), 0.9 (t-Bu), 1.1–2 (CH2 CH), 3.7 (CH2 Ar), 4.5 (CH2Cl), 6.6–7.2 (Ar H).
0.1 (CH3 Si), 1–2.3 (CH2 CH), 3.4 (CH2 Ar), 4.5 (CH2Cl), 6.1–7.1(Ar H).
0.65 (CH2 Si), 0.98 (CH3), 1.20–2.50 (CH2 CH), 2.78 (Ar CH2), 6.60–7.26 (Ar C H).
0.48–0.53 (SiCH3), 0.89–1.00 (t Bu), 1.04–2.30 (CH2 CH), 2.79–3.02 (Ar CH2), 6.60–7.26 (Ar C H).
0.09 (CH3 Si), 1.2–1.9 (CH2 CH), 2.8 (CH2 Ar), 4.5 (CH2Cl), 6.4–7.5 (Ar H).
0.09 (CH3 Si), 1.1–1.9 (CH2 CH), 2.2 (CH2 Ar), 4.5 (CH2Cl), 6.6–7.2 (Ar H).
Heteroatom Chemistry DOI 10.1002/hc

420 Assadi, Mahkam, and Tajrezaiy
FIGURE 3 1H NMR spectrum of VI.
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Heteroatom Chemistry DOI 10.1002/hc