Precision Synthesis of ω-Branch, End-Functionalized Comb Polystyrenes Using Living Anionic Polymerization and Thiol-Ene Click Chemistry

A combination of living anionic polymerization and thiol-ene click chemistry provides an efficient and convenient method for synthesis of well-defined comb polystyrenes with precisely controlled architecture details and a wide selection of functionalities. omega-(p-Vinylbenzyl)polystyrene macromonomer was synthesized by sec-butyllithium-initiated polymerization of styrene followed by termination with 4-vinylbenzyl chloride (VBC). For the synthesis of alpha-4-pentenyl-omega-(p-vinylbenzyl)polystyrene macromonomer, an unsaturated initiator, 4-pentenyllithium, was used followed by termination with VBC. To ensure successful living anionic polymerization of macromonomers, impurities present in the macromonomers and glass reactors were readily removed by titration with excess sec-butyllithium initiator right before initiation, resulting in polymacromonomers with controlled M-n (74 000, 130 000 g/mol) and narrow M-w/M-n. Living anionic copolymerization of mixtures of both types of macromonomers yielded a well-defined comb-shape precursor with controlled fractions of omega-vinyl branch end groups, which were subsequently subjected to facile and efficient functionalization by photoinitiated thiol-ene click reactions with diverse functional groups (-OH, -CO2H, and -C8F17). Characterization by NMR, SEC, and MALDI-TOF mass spectrometry established their chemical structures and chain-end functionalities, which indicates precisely defined comb polystyrenes with controlled degrees of functionalization.