Cycloalkenyl-Functionalized Polymers and Block Copolymers: Syntheses via Selective RAFT Polymerizations and Demonstration of Their Versatile Reactivity

A facile synthetic strategy for the preparation of well-defined polymers hearing cycloalkenyl side groups has been established via selective reversible addition-fragmentation chain transfer (RAFT) polymerization of cycloalkene-functionalized asymmetrical divinyl monomers. Two representative monomers, 4-(6'-methylcyclohex-3'-enylmethoxy)-2,3,5,6-tetrafluorostyrene and 4-(cyclohex-3'-enylmethoxy)-2,3,5,6-tetrafluorostyrene, were synthesized. RAFT polymerizations of these bifunctional monomers, using S-1-dodecyl-S'-(alpha,alpha'-dimethyl-(alpha ''-acetic acid)trithiocarbonate as the chain transfer agent and 2,2'-azobis(isobutyronitrile) (AIBN) as the thermal initiator, exhibited superb selectivity toward the substituted styrenyl vinylic unit relative to the cyclohexenyl unit, even at high monomer conversions (>80%). The resulting polymers retained quantitative cyclohexenyl groups, while having predetermined molecular weights and narrow molecular weight distributions (PDI = 1.09-1.15). Well-defined block copolymers with pendent cyclohexenyl groups were also prepared by sequential RAFT chain extension polymerizations. A variety of functional polymers were further obtained by functional group transformations using the cyclohexene-functionalized polymers as precursors.