The reactions could be readily carried out due to the strong nucleophilictiy and
steric accessibility of the number 3 position nitrogen atom in 1-
vinylimidazole and high reactivity of 1-bromobutane and methyl
iodide. Both [VBI]Br and [VMI]I are soluble in water, alcohols and
DMF, insoluble in ethyl ether, chloroform and tetrahydrofuran.
The copolymers for preparing OH form anion exchange
membranes based on two types of imidazolium ionic liquid
monomers were synthesized via free radical polymerization, as
mentioned in Section 2.3. The synthetic routes are shown in
Scheme 2 and Scheme 3. Because of the strong water affinity of
imidazolium ionic liquids, styrene was introduced to the polymer
backbone to adjust the hydrophilic-lipophilic balance of the
membranes. The properties of the copolymers could be tuned by
varying the monomer ratios in the reactants.
The feed ratio of IILs/styrene, nitrogen content of copolymers
and the molar ratio of IILs/styrene in copolymers are summarized
in Table 1. Sample A, B and C were polymerized by [VBI]Br with
styrene, while Sample D, E and F were polymerized by [VMI]I with
styrene. The Nitrogen only existed in the imidazolium cation
groups, hence, the amount of imidazolium groups in the copolymers
could be reflected by the nitrogen content and controlled
by varying the feed ratio of IILs/styrene. It can be seen in Table 1
that the nitrogen content of copolymers decreased with the
decreasing amount of ionic liquids. All the copolymers and OH
form anion exchange membranes obtained in this work are soluble
in alcohols and DMF, insoluble in ethyl ether, chloroform and
tetrahydrofuran. Thus, the membranes could be prepared by solution
casting method mentioned in Section 2.4.
Fig. 1 shows the results of FT-IR spectra analysis of IILs and
membranes. The strong peaks between 2800 and 3000 cm1 are
the characteristics of methyl and methane of the branch of imidazolium
cation. The sharp peak at 1572 cm1 is identified to the
stretching vibration of C]N and the peak at 1162 cm1 is identified
to the flexural vibration of CeH in the imidazole ring.