Synthesis and characterization of amphiphilic
diblock copolymers of 2-(1-imidazolyl)ethyl
methacrylate and styrene
Maria Rikkou-Kalourkoti, Panayiota A. Panteli and Costas S. Patrickios
*
Six amphiphilic diblock copolymers based on the hydrophilic monomer 2-(1-imidazolyl)ethyl methacrylate
(ImEMA) and the hydrophobic monomer styrene (Sty) were prepared by sequential reversible addition–
fragmentation chain transfer (RAFT) polymerization. RAFT polymerization was performed via the use of
4-cyano-4-(dodecylsulfanylthiocarbonylsulfanyl)pentanoic acid (CDP) as the chain transfer agent and
glacial acetic acid as the solvent. Amphiphilic diblock copolymers with a range of compositions were
prepared, with ImEMA first blocks of constant (nominal) degree of polymerization (DP) equal to 100, and
Sty second blocks of a DP between 18 and 482, having ImEMA contents between 15 and 80 mol%, as
measured by
1
H NMR spectroscopy in CDCl
3
. Only the Sty-rich ($51 mol%) diblock copolymers were
fully soluble in the solvent for gel permeation chromatography (GPC), tetrahydrofuran; GPC analysis of
these copolymers indicated molecular weights in the range of 15 to 34 kDa, and molecular weight
dispersities ranging from 1.1 to 1.6. At room temperature, the side-group of the ImEMA units was stable
in an acidic environment but hydrolyzed slowly under alkaline conditions. In bulk neutral samples, the
ImEMA side-group was thermally stable up to 250
C. Finally, dynamic light scattering and polarized
light microscopy indicated that the Sty-rich diblock copolymers formed spherical micelles in chloroform,
whereas all diblock copolymers formed anisotropic nanophases in water.
Introduction
Imidazole is a heterocyclic aromatic molecule bearing two
nitrogen atoms, conferring to it high polarity.
1–3
The imidazole
ring has great biological importance, appearing in many bio-
logical molecules including the side-group of histidine which is
the main component of histones, and is part of the serine
catalytic triad found in a certain type of proteases.
4
Because of
its biological importance, the imidazole ring has been intro-
duced in many types of synthetic polymers, including
vinylics,
1–3,5–10
methacrylates
11–15
and styrenics.
16
Apart from the
polymerization of monomers bearing neutral imidazole side-
groups, the polymerization of monomers with pendant imida-
zolium salts has also been reported and currently receives great
attention because of their action as ionic liquids.
17–22
In most cases, imidazole has been introduced via its vinylic
monomers, such as N-vinylimidazole (NVIm) or 4-vinyl-
imidazole (4VIm). For example, NVIm was used for the prepa-
ration of its linear homopolymers,
3
its amphiphilic random
copolymers with ethyl methacrylate (EMA),
5
and its randomly-
crosslinked amphiphilic copolymer conetworks with poly-
(tetrahydrofuran)
6,7
using free radical polymerization, as well as
the preparation of double-hydrophilic diblock copolymers with
N-isopropylacrylamide
8
and amphiphilic diblock copolymers
with styrene
10
using reversible addition–fragmentation chain
transfer (RAFT) polymerization. Regarding the other vinylic
imidazole-containing monomers, Long et al. reported the use of
4VIm
2,9
for the synthesis of linear homopolymers and diblock
and ABA triblock copolymers with di(ethylene glycol)methyl
ether methacrylate,
9
using RAFT polymerization. There is also
one example of a styrenic imidazole-containing monomer used
for the preparation of random copolymers with n-butyl acrylate
using nitroxide-mediated radical polymerization (NMP).
16
Additionally, imidazole-containing methacrylate monomers
have also been prepared and polymerized. In particular, 2-[(1-
imidazolyl)formyloxy]ethyl methacrylate was used for the
preparation of its homopolymers,
11
and 2-(1-imidazolyl)ethyl
methacrylate (ImEMA) was used for the preparation of its
homopolymers,
12
its double-hydrophilic diblock copolymers
with 2-(dimethylamino)ethyl methacrylate,
13
its ampholytic
diblock copolymers with methacrylic acid,
15
and its end-linked
homopolymer networks,
14
by free radical polymerization
11
and
group transfer polymerization (GTP).
12–15
Finally, imidazole-
bearing (co)polymers were recently prepared by Lowe and
coworkers
23
via a polymer modication strategy, and, in partic-
ular, through the acyl substitution reaction of penta-
uorophenyl acrylate units with histamine [2-(1H-imidazol-4-yl)-
ethanamine]. Herein, we report for the rst time the use of
ImEMA for the synthesis of its amphiphilic diblock copolymers
Department of Chemistry, University of Cyprus, P. O. Box 20537, 1678 Nicosia, Cyprus.
E-mail: kalourk@ucy.ac.cy; ppante02@ucy.ac.cy; costasp@ucy.ac.cy
Cite this: DOI: 10.1039/c4py00221k
Received 15th February 2014
Accepted 24th March 2014
DOI: 10.1039/c4py00221k
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