Stacy J. Taylor and Robson F. Storey
3,3′,5,5′-Tetrakis(2-chloro-2-propyl)biphenyl (biphenyl tetracumyl chloride, BPTCC) and 1,3-bis[3,5-bis(2-chloro-2-propyl)phenoxy]propane (diphenoxypropane tetracumyl chloride, DPPTCC) were synthesized as initiators for quasiliving cationic polymerization of isobutylene (IB). In the synthesis of BPTCC, tetrafunctionality was achieved via the coupling of dimethyl 5-bromoisophthalate (DMBI) using nickel dibromide bis(triphenylphosphine) and zinc in the presence of a base; in the synthesis of DPPTCC, two equivalents of dimethyl 5-hydroxyisophthalate were linked via reaction with 1,3-dibromopropane in the presence of potassium carbonate. Both initiators were used to initiate the polymerization of IB under quasiliving cationic polymerization conditions. PIB initiated from BPTCC revealed a chain end/molecule value (as determined by 1H-NMR) of 3.85, verifying the nearly exclusive production of 4-arm polyisobutylene (PIB). GPC analysis revealed a narrow peak representing the target four-arm PIB, with a slight shoulder at high elution volumes (low molecular weights). GPC analysis of the PIB initiated by DPPTCC revealed multimodal distributions, suggesting the formation of two-, three-, and four-arm star polymers during the polymerization. This behavior was attributed to Friedel–Crafts alkylation of the initiator core after the addition of one IB unit, which was activated by the electron-donating oxytrimethyleneoxy linking moiety.