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

Abstract 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 TiCl 4 . 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.