Facile incorporation of natural carboxylic acids into polymers via polymerization of protic ionic liquids

Article abstract of DOI:10.1002/pola.25882

This communication reports on the facile incorporation of natural carboxylic acids such as acetic acid or oleic acid into new ionic polymers. A series of protic ionic liquid monomers derived from natural carboxylic acids and N-(2-(dimethylamino)ethyl) methacrylate were easily polymerized. This method represents route to incorporate natural products into polymer latexes.

Full text of DOI:10.1002/pola.25882

WWW.POLYMERCHEMISTRY.ORG
RAPID COMMUNICATION
Facile Incorporation of Natural Carboxylic Acids into Polymers via
Polymerization of Protic Ionic Liquids
Mo´ nica Moreno,1 M. Ali Aboudzadeh,1 Maria J. Barandiaran,1 David Mecerreyes1,2
1Institute for Polymer Materials (POLYMAT) and Grupo de Ingenier´ıa Quı´mica Kimika Aplikatuko Departamentua, University of
the Basque Country (UPV-EHU), Joxe Mari Korta Center, Avda. Tolosa 72, 20018 Donostia-San Sebastian, Spain
2Ikerbasque, Basque Foundation for Science, E-48011 Bilbao, Spain
Correspondence to: D. Mecerreyes (E-mail: david.mecerreyes@ehu.es)
Received 31 October 2011; accepted 1 December 2011; published online 21 December 2011
DOI: 10.1002/pola.25882
KEYWORDS: emulsion polymerization; ionic liquids; ionomers; polyelectrolytes; radical polymerization
INTRODUCTION The development of materials using prod-
ucts from natural and renewable resources is receiving an
increased attention. The high price and future lack of fossil
fuels are creating doubts about the sustainability for the
actual polymer industry. For these reasons, there is a grow-
ing interest in the use of natural products for the develop-
ment of polymers, which match or even improve the per-
formance of the actual oil-based polymeric materials.1–3
Carboxylic acids are widespread in nature and some of
them such as lactic, itaconic, or fatty acids are already im-
portant raw materials for the synthesis of a number of
industrial relevant polymers such as biodegradable polyest-
ers, specialty polyamides and polyurethanes. However, there
is a need for new synthetic routes for the incorporation of
other natural carboxylic acids into advanced polymeric
materials.
EXPERIMENTAL
Materials and Methods
Acetic acid (>99.5%), butyric acid (>99.5%), hexanoic acid
(>99.5%), benzoic acid (>99.5%), octanoic acid (>98%),
oleic acid (puriss), 2-(dimethylamino)ethyl methacrylate
(98%), 2,20-azobis(2-methylpropionamidine) (AIBA) (97%),
and 2,20-azobis(2-methylpropionitrile (AIBN) (98%) were
purchased in Aldrich and used without purification.
The 1H and 13C NMR measurements were carried out on a
Bruker AC-500 instrument. The samples were dissolved in deu-
terated CDCl3, and the solutions were measured with tetrame-
thylsilane as an internal reference. Fourier transform infrared
(FTIR) measurements were conducted on a Nicolet Magna-IR
560 spectrometer. Gel permeation chromatography–size exclu-
sion chromatography (GPC–SEC) with light-scattering detection
was used to determine the molecular weight of the polymers
using a water/acetonitrile (80:20ꢀ) eluent with 0.25 mol/L NaCl
and 0.03 mol/L NaH2PO4 at 25 C and a rate of 0.8 mL/min.
Water SEC was performed in a water SEC equipped with three
columns (Ultrahydrogel 200, 250, and 150) and a MiniDawn
Treos (Wyatt) light-scattering detector and an Optilab T-rex
(Wyatt) refractive index detector. Differential scanning calorim-
etry (DSC) was measured in a TA Instruments Q1000 equip-
ment. The scanning cycles consisted of a first cooling to ꢁ80 ꢀC,
The introduction of new ionic moieties, cations and anions,
coming from ionic liquids chemistry is extending the proper-
ties and classical applications of polyelectrolytes4 to other
fields such as energy,5 supramolecular polymers,6 gas mem-
branes,7 or stimuli responsive materials.8 These new polye-
lectrolytes are being named polymeric ionic liquids or poly(-
ionic liquids) in analogy to their monomeric constituents.
Poly(ionic liquids) are classically obtained by polymerization
of nonprotic ionic liquid monomers. However, there is a sec-
ond class of ionic liquids, named protic ionic liquids (PILs),9–
ꢀ
ꢀ
then heating to 100 C at 20 C/min. Thermogravimetric test
were measured in a TGA 2950/Q500 at 10 /min under nitro-
gen from room temperature to 500 ꢀC.
ꢀ
12
which have been only investigated in polymer science for
the development of new polyelectrolytes and proton con-
ducting fuel cell membranes. PILs are easily synthesized by
the neutralization and subsequent proton transfer between a
Brønsted acid and a base. The aim of this communication is
to report the facile incorporation of natural carboxylic acids
into polymers via PIL monomer chemistry and their subse-
quent polymerization.
General Procedure for the Synthesis of Protic Ionic
Liquid Monomers
In a typical reaction, for HDMAEMA-butyrate: 2-(dimethyla-
mino)ethyl methacrylate (5056 g, 32 mmol) and butyric acid
(2833 g, 32 mmol) were simultaneously added dropwise to
a three-necked round bottom flask under vigorous stirring in
Additional Supporting Information may be found in the online version of this article.
C
V
2011 Wiley Periodicals, Inc.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 1049–1053
1049

RAPID COMMUNICATION
WWW.POLYMERCHEMISTRY.ORG
nitrogen atmosphere. The proton transfer reaction was car-
ried out for 30 min and the obtained 2-(dimethylammoniu-
m)ethyl methacrylate-butyrate (HDMAEMA-butyrate) PIL
was characterized. 1H NMR (500 MHz, CDCl3, d ppm) 6.14
(s, 1H, ¼¼CH), 5.59(s, 1H, CH), 4.34(t, 2H, ACOOCH2, 2.82 (s,
2H, CH2AN), 2.41 (s, 6H, CH3N), 2.27 (t, 2H, CH2ACOO),
1.96 (s, 3H, CH3AC¼¼), 1.65 (m, 2H, ACH2A), 0.97 (t, 3H,
CH2ACH3). 13C NMR (500 MHz, CDCl3, d ppm) 177.16,
166.37, 135.48, 125.29, 60.58, 56.30, 43.63, 36.83, 18.19,
17.66, and 13.30.
SCHEME 1 Proposed reaction for the synthesis of monomeric
PILs.
The reactor was purged with N2 for 30 min and then
immersed in an oil bath at 70 ꢀC for 3 h. After polymeriza-
tion, the water was eliminated by evaporation in the rotavap
and the polymer conversion was analyzed by 1H NMR
(>95% in all the cases). 1H NMR (500 MHz, CDCl3, d ppm)
4.11 (s, 2H, ACOOCH2, 2.69 (s, 2H, CH2AN), 2.4–2.3 (m, 8H,
CH3N), 2.25–1.7(m, 2H, ACH2ACOO), 1.65 (m, 2H,
COACH2ACH2A), 1.35–125 (m, 4H, ACH2ACH2A), and
1.25–0.75 (m, 6H, ACH3). GPC–SEC in water equipped with
light-scattering detector gave a Mw ¼ 1.287 ꢂ 105 g/mol;
Mw/Mn ¼ 1.53.
Same procedure was used for the other monomers.
HDMAEMA-acetate: 1H NMR (500 MHz, CDCl3, d ppm) 6.12
(s, 1H, ¼¼CH), 5.58(s, 1H, CH), 4.34(t, 2H, ACOOCH2, 2.86 (s,
2H, CH2AN), 2.44 (s, 6H, CH3N), 1.99 (s, 3H, CH3AC¼¼), and
1.94 (s, 3H, ACH3ACOO).13C NMR (500 MHz, CDCl3, d ppm)
174.82, 166.07, 135.48, 125.22, 60.21, 55.63, 21.03, and
17.39. HDMAEMA-hexanoate: 1H NMR (500 MHz, CDCl3, d
ppm) 6.15 (s, 1H, ¼¼CH), 5.60 (s, 1H, CH), 4.34 (t, 2H,
ACOOCH2, 2.81 (s, 2H, CH2AN), 2.41 (s, 6H, CH3N), 2.27 (t,
2H, CH2ACOO), 1.96 (s, 3H, CH3AC¼¼), 1.65 (m, 2H,
COACH2ACH2A), 1.34 (t, 4H, ACH2ACH3), and 0.90 (t,
ACH3). 13C NMR (500 MHz, CDCl3, d ppm) 177.16, 166.37,
135.48, 125.29, 60.58, 56.30, 43.63, 36.83, 18.19, 17.66, and
13.30.
General Procedure for Emulsion Polymerization of
HDMAEMA-Oleate
In a typical experiment, a poly(HDAMAEMA-oleate) latex was
synthesized by charging 3 g of HDMAEMA-oleate monomer,
0.006 g of surfactant Disponil A (nonionic), 0.003 g of AIBN
initiator to a 100-mL glass reactor filled with 60 mL of water.
The reactor was purged with N2 for 30 min and then
immersed in an oil bath at 70 ꢀC for 4 h. Reaction was carried
out under N2 at a stirring rate of 150 rpm. After the reaction,
the monomer conversion was measured by 1H NMR (88%).
HDMAEMA-octanoate: 1H NMR (500 MHz, CDCl3, d ppm)
6.15 (s, 1H, ¼¼CH), 5.60(s, 1H, CH), 4.34 (t, 2H, ACOOCH2,
2.81 (s, 2H, CH2AN), 2.41 (s, 6H, CH3N), 2.27 (t, 2H,
CH2ACOO), 1.96 (s, 3H, CH3AC¼¼), 1.65 (m, 2H,
COACH2ACH2A), 1.34 (t, 4H, ACH2A CH3), and 0.90 (t,
ACH3). 13C NMR (500 MHz, CDCl3, d ppm) 177.05, 166.11,
135.36, 125.04, 60.43, 56.82, 43.45, 34.49, 30.74, 24.37,
21.75, 18.01, and 13.23. HDMAEMA-oleate: 1H NMR (500
MHz, CDCl3, d ppm) 6.15 (s, 1H, ¼¼CH), 5.60(s, 1H, CH), 5.40
(s, 2HA CH¼¼), 4.34 (t, 2H, ACOOCH2, 2.81 (s, 2H, CH2AN),
2.41 (s, 6H, CH3N), 2.30 (t, 2H, CH2ACOO), 2.08 (m, 4H,
CH2ACH¼¼), 1.96 (s, 3H, CH3AC¼¼), 1.65 (m, 2H,
COACH2ACH2A), 1.29 (t, 16H, ACH2A), and 0.90 (t, 3
ACH3). 13C NMR (500 MHz, CDCl3, d ppm) 176.79, 165.93,
135.40, 129.64,124.92, 127.32, 60.42, 56.23, 43.47,34.48,
30.74, 29.13, 28.72, 28.57, 26.55, 24.96, 22.04, 17.51and
13.41.
RESULTS AND DISCUSSION
At first, a series of PIL monomers were synthesized by react-
ing a methacrylic Brønsted base such as the tertiary amine,
N-(2-(dimethylamino)ethyl) methacrylate (DMAEMA) with
different carboxylic acids such as acetic acid, butyric acid,
hexanoic or caproic acid, octanoic or caprylic acid, benzoic
acid, and oleic acid (Scheme 1). The reactants were mixed at
room temperature by simultaneous addition in an equimolar
amount as neat liquids to eliminate the effects of the exo-
thermic neutralization reactions. By this method, a series of
protic ionic monomers were readily synthesized without
need of purification steps. As the PILs are formed by neutral-
ization reaction, a possible equilibrium may exist and usually
the proton transfer is incomplete, resulting in the formation
of neutral ion-pairs. The difference in pKaaq values between
the acid and the base and their chemical nature is still a
matter of discussion in the ionic liquid community although
a value of DpKaaq > 6 seem to be enough for full ionization.
In our case, all the monomer characterizations were in good
1
HDMAEMA-benzoate: H NMR (500 MHz, CDCl3, d ppm) 8.07
(s, 2H, arom), 7.50 (s, 1H, arom), 7.41 (s, 2H, arom), 6.15 (s,
1H, ¼¼CH), 5.56 (s, 1H, CH), 4.44 (t, 2H, ACOOCH2, 3.02 (s,
2H, CH2AN), 2.58 (s, 6H, CH3N), and 1.94 (s, 3H, ACH3). 13C
NMR (500 MHz, CDCl3, d ppm) 170.81, 166.05, 135.05,
133.28, 131.01, 130.79, 127.44, 122.51, 59.80, 55.90, 42.96,
and 17.44.
General Procedure for Free Radical Polymerization of
Protic Ionic Liquid Monomers
Methacrylic PIL monomers (HDMAEMA-acetate, HDMAEMA-
1
accordance to PILs formation due to the shift in the H NMR
butyrate,
HDMAEMA-hexanoate,
HDMAEMA-octanoate,
signals associated to the methylene group near to the nitro-
gen atom and the methylene group near to the carboxylate
together with the appearance of a new band in the carboxy-
late region of the FTIR (1550–1600 cmꢁ1) (Supporting infor-
mation, Fig. S1).
HDMAEMA-benzoate, and HDMAEMA-oleate) were polymer-
ized using conventional free radical polymerization. Typically,
to a 50-mL glass reactor, monomer (HDMAEMA-hexanoate, 2
g), AIBA (0.01 g), and distilled water (40 g) were charged.
1050
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 1049–1053

WWW.POLYMERCHEMISTRY.ORG
RAPID COMMUNICATION
yield (>95%) as verified by 1H NMR. Water-soluble poly-
mers were obtained in the case of poly(N-dimethylammo-
nium-2-ethyl methacrylate) poly(HDMAEMA) having acetate,
butyrate, hexanoate, and benzoate counter anions. In the
case of poly(HDMAEMA) with octanoate and oleate counter-
anions, the obtained polymers were not soluble in water.
The obtained polymers were characterized by nuclear mag-
netic resonance (NMR), FTIR spectroscopy, GPC–SEC, and
DSC. Figure 1 shows, as an example, the 1H NMR spectrum
of poly(HDMAEMA-hexanoate). A signal associated to the
transferred proton at 4.53 ppm and a shift in the signals
associated to the methylene group near to the nitrogen atom
and the methylene group close to the carboxylate indicates
the protic ionic nature of the polymer. Further evidence was
observed in the carboxylate region of the FTIR. Here, two
bands were observed: the first one at 1722 cmꢁ1 due to the
ester of the polymethacrylic backbone and a second band at
1590 cmꢁ1due to the carboxylate pendant counter-anion.
The polymers were also characterized by GPC–SEC using
light scattering detector. The average weight molecular
weights (Mw) ranged for all polymers between 1 ꢂ 105 and
6 ꢂ 105 g/mol and polydispersity values from 1.4 to 1.6 as
expected for free radical polymerization in water.
SCHEME 2 Free radical polymerization of monomeric PILs
based on DMAEMA and natural carboxylates.
Next step, polymerization of monomeric PILs was carried
out using free radical polymerization conditions (Scheme 2).
Although long alkyl carboxylic acids are not soluble in water,
due to their ionic character all the monomers including the
ones with the long alkyl carboxylates such as hexanoate
(C6), octanoate (C8), or oleate (C18) solubilized in water at
5 wt % concentration. Thus, polymerizations were carried
out in water at 70 ꢀC using a water-soluble radical initiator,
2,20-azobis(2-methylpropionamidine)dihydrochloride (AIBA).
After 3 h reaction time, polymerizations proceeded in high
Figure 2 shows the DSC curves of four of the protic ionic
polymers. As expected, all the polymers are amorphous and
show a decreasing glass transition depending on the carbox-
ylate flexible chain. Whereas, poly(HDMAEMA-benzoate) has
ꢀ
a glass transition (Tg) of 15 C, the acetate polymer has a Tg
FIGURE 1 1H NMR of poly(N-dimethylammonium-2-ethyl methacrylate hexanoate) in CDCl3.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 1049–1053
1051

RAPID COMMUNICATION
WWW.POLYMERCHEMISTRY.ORG
phase to the polymer particles. Because of this, alternative
strategies such as miniemulsion polymerization have been
proposed for polymerizing fatty acid containing monomers.13
Interestingly, our PIL monomer HDMAEMA-oleate is more
hydrophilic than their fatty acids methacrylic ester equiva-
lent. As a result, conventional emulsion polymerization could
be successfully applied to the homopolymerization
HDMAEMA-oleate monomer. Thus, emulsion polymerization
was carried out at 70 ꢀC under mechanical stirring and
nitrogen atmosphere using Disponil A (nonionic) as emulsi-
fier. After 3 h reaction time, a polymer latex was obtained
showing a particle size of 230 nm which was already stable
for more than five months. Further works are being carried
out to exploit the versatility of this monomers to incorporate
natural carboxylates into functional copolymer latexes
obtained by emulsion polymerization.
FIGURE 2 DSC thermograms (20 ꢀC/min) of the protic ionic
polymers (a) poly(HDMAEMA-benzoate), (b) poly(HDMAEMA-ac-
etate), (c) poly(HDMAEMA-butyrate), and (d) poly(HDMAEMA-
hexanoate).
CONCLUSIONS
In conclusion, a series of natural carboxylic acids were incor-
porated into polymers via simple PIL monomer chemistry
and their subsequent free radical polymerization. The poly-
mers show protic ionic characteristics including an amphi-
pathic nature, glass transition, and thermal stability depend-
ency in the type of carboxylate counter-anion. As a potential
application, this chemistry can be used to incorporate fatty
acids and other natural carboxylic acids into polymer latexes.
ꢀ
ꢀ
of 4 C, the butyrate a Tg of ꢁ24 C, and the hexanoate a Tg
ꢀ
of ꢁ34 C. Further decreases of Tg are seen for the octanoate
and oleate polymers which showed very broad transitions
between ꢁ70 ꢀC and ꢁ30 ꢀC which made difficult to deter-
mine the exact value.
ACKNOWLEDGMENT
It is worth to remember that PILs are considered as interme-
diate compounds between fully ionic liquids, such as the
widely available dialkylimidazolium salts, and molecular
liquids such as hydrocarbons, alcohols, and water. For this
reason, PILs are amphipathic molecules which in some cases
can be miscible with polar solvents such as water and also
nonpolar ones such as hexane. This property is translated
into our polymers. For instance, all the protic ionic polymers
are soluble in water with the exception of the poly(-
HDMAEMA-octanoate) and -oleate having long alkyl carboxy-
lates which are soluble in nonpolar solvents such as toluene,
ethyl ether, and hexanes. Besides, all the polymers are solu-
ble in solvents of intermediate polarity such as methanol
and chloroform. Another consequence of the intermediate
ionicity of the PILs is their lower thermal stability with
respect to the nonprotic ionic liquids. This fact is translated
to the thermal stability of our polymers. Here, an increase in
the chain length of the carboxylic acid resulted in a decrease
in the thermal decomposition temperature of the polymers.
Hence, the thermal decomposition temperature at 50%
weight loss (T50%) is 330 ꢀC for the poly(HDMAEMA-ace-
The financial support of the Spanish Ministerio de Ciencia e
Innovacio´n through projects (CTQ2006-03412 and MAT2011-
27993) is acknowledged.
REFERENCES AND NOTES
1 Gandini, A. Macromolecules 2008, 41, 9491–9504.
2 Jasinska, L.; Koning, C. E. J. Polym. Sci. Part A: Polym.
Chem. 2010, 48, 2885–2895.
3 Mar´ın, R.; Martinez de Ilarduya, A.; Mun˜ oz-Guerra, S.
J. Polym. Sci. Part A: Polym. Chem. 2009, 47, 2391–2407.
4 Mecerreyes, D. Prog. Polym. Sci. 2011, 36, 1629–1648.
5 (a) Shaplov, A. S.; Lozinskaya, E. I.; Vygodskii, Y. S. In Elec-
trochemical Properties and Applications of Ionic Liquids; Tor-
riero, A. A. J.; Shiddiky M., Eds.; Nova Science Publishers:
New York, 2010, pp 203–298. ISBN 978–1-61728–942-2; (b)
Appetechi, G. B.; Kim, G. T.; Montanina, M.; Carewska, M.;
Marcilla, R.; Mecerreyes, D.; De Meatza I. J. Power Sources
2010, 195, 3668–3675.
6 (a) Lee, S.; Cummings, M. D.; Willing, G. A.; Firestone, M. A.
J. Mater. Chem. 2009, 19, 8092–8101; (b) Cheng, S.; Zhang, M.;
Wu, T.; Hemp, S. T.; Mather, B. D.; Moore, R. B.; Long, T. E.
J. Polym. Sci. Part A: Polym. Chem. 2012, 50, 1–198.
ꢀ
ꢀ
tate)ꢀ, 312 C for the butyrate, 225 C for the octanoate, and
216 C for the oleate polymer, respectively (Supporting infor-
mation, Fig. S2).
7 (a) Bara, J. E.; Camper, D. E.; Gin, D. L.; Noble, R. Acc. Chem.
Res. 2010, 43, 152–159; (b) Gu, Y.; Lodge, T. P. Macromolecules
2011, 44, 1732–1736.
As a potential application of this monomer chemistry, the
possibility of incorporating fatty acids in latexes was investi-
gated. It is well known that the conventional emulsion poly-
merization of hydrophobic monomers derived from fatty
acids such as oleyl or lauryl methacrylate does not proceed
because of their slow migration kinetics through the aqueous
8 (a) Vijayakrishna, K.; Jewrajka, S. K.; Ruiz, A.; Marcilla, R.;
Pomposo, J. A.; Mecerreyes, D.; Taton, D.; Gnanou, Y. Macro-
molecules 2008, 41, 6299–6308; (b) Dobbelin, M.; Jovanovski,
¨
V.; Llarena, I.; Claros-Marfil, L. J.; Caban˜ ero, G.; Rodriguez, J.;
Mecerreyes, D. Polym. Chem. 2011, 2, 1275–1278.
1052
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 1049–1053

WWW.POLYMERCHEMISTRY.ORG
RAPID COMMUNICATION
9 (a) Greaves, P. L.; Drummond, C. J. Chem. Rev. 2008, 108,
206–2037; (b) Stoimenovski, J.; Izgorodina, E. I.; MacFarlane D.
R. Phys. Chem. Chem. Phys. 2010, 12, 10341–10347; (c) Anouti,
M.; Caillon-Caravanier, M.; Le Floch, C.; Lemordant D. J. Phys.
Chem. B 2008, 112, 9406–9411.
11 Belieres, J. -P.; Angell, C. A. J. Phys. Chem. B 2007, 111,
4926–4937.
12 Stoimenovski, J.; Izgorodina, E.; MacFarlane, D. R. Chem.
Phys. Phys. Chem. 2010, 12, 10341–10347.
13 (a) Asua, J. M. Prog. Polym. Sci. 2002, 27, 1283–1346; (b)
Quintero, C.; Mendon, S. K.; Smith, W.; Thames, S. F. Prog.
Org. Coat. 2006, 57, 195–201.
10 Burrell, G. L.; Burgar, I. M.; Separovic, F.; Dunlop, N. Phys.
Chem. Chem. Phys. 2010, 72, 1571–1577.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 1049–1053
1053