Highly efficient synthesis of random isobutylene/alkenyl styrene copolymers with pendant vinyl groups via cationic polymerization for versatile functionalization

Abstract

The controlled/living cationic copolymerizations of isobutylene (IB) with alkenyl styrenes including 4-allylstyrene (AS), p-(3-butenyl)-styrene (BS) and p-(5-hexenyl)-styrene (HS) were carried out in n-hexane/CH₂Cl₂ (6/4 v/v) at −80 °C using a t-BuCl/FeCl₃/iPrOH initiating system. The random copolymers of IB with AS, BS or HS could be obtained without crosslinking and the contents of AS units in the copolymers linearly increased from 0.71 mol% to 14.23 mol% with an increase in the feed ratio of AS. The monomer reactivity ratios (r) were determined to be r_AS = 4.16 and r_IB = 1.66 by the Fineman–Ross method, respectively. The livingness of cationic copolymerization of IB with AS was confirmed by All Monomer In (AMI) and Incremental Monomer Addition (IMA) techniques at −80 °C. The yields, M_n and M_w/M_n of the resulting copolymers decreased with increasing polymerization temperature (T_p) and the apparent activation energy (E_a) depended on T_p. The pendant vinyl groups in the above poly(IB-co-AS) copolymers can be completely converted into hydroxyl groups, carboxyl groups or epoxy groups via hydroboration/oxidation, thiol–ene click reaction or epoxidation. The hydrophilicity on the film surface of functionalized copolymers with hydroxyl, carboxyl or epoxy pendant groups could be improved by introduction of the functional groups and the water contact angle (WCA) of poly(IB-co-AS) with epoxy pendant groups decreased from 134.9° to 78.7° upon increasing the molar content of epoxy groups from 0 to 3.99%. Therefore, the random isobutylene/alkenyl styrene copolymers containing plentiful pendant vinyl groups and versatile polar groups would have potential applications in highly reactive elastomers, adhesives and amphiphilic materials with inorganic fillers.