Synthesis of branched polyisobutylenes via cationic copolymerization of p-chloromethylstyrene and isobutylene

Branched polyisobutylenes (PIBs) with relatively low dispersities (1.4–1.8) and benzylic halide functionalities are synthesized by self-condensing vinyl cationic copolymerization of p-chloromethylstyrene (p-CMS) and isobutylene (IB) coinitiated by TiCl₄. It is found that the [IB]/[p-CMS] feed ratio plays a crucial role for the initiating behavior of p-CMS: the initiation arising from p-CMS is suppressed at [IB]/[p-CMS] ≥17; in contrast, the pendant benzyl chloride moiety of p-CMS monomer in the formed copolymer chains can initiate branching reactions. The resulting branched PIBs are of a gradient composition as well as a gradual increase in branching density due to large disparity in reactivity ratios. This strategy is successfully employed to create branched PIBs with low to moderate molecular weights (M_n, 5 k–78 k Da) through controlling the monomer/initiator mole ratio. However, it is shown that this method failed to obtain branched PIBs with high M_n, bearing a complicated copolymerization mechanism.