Anionic Synthesis of Mono- and Heterotelechelic Polystyrenes via Thiol-Ene Click Chemistry and Hydrosilylation

A series of precisely defined, mono- and heterotelechelic polystyrenes have been facilely synthesized by combining living anionic polymerization with other efficient chemical transformations, such as thiol-ene click chemistry and hydrosilylation reactions, leading to a versatile and general functionalization methodology for chain-end-functionalized anionic polymers. Specifically, alpha-vinyl-ended poly(styryl)lithiums, which were prepared using 4-pentenyllithium as an initiator under high-vacuum conditions, were reacted with different end-capping reagents using living functionalization methods to afford various chain-end functionalities quantitatively, namely, alpha-vinylpolystyrene, alpha-vinyl-omega-hydroxylpolystyrene, and alpha-vinyl-omega-hydrosilylpolystyrene. Subsequent functionalizations using photoinitiated thiol-ene click chemistry and hydrosilylation reactions allow facile and efficient installation of diverse functionalities onto the alpha- and omega-chain ends of these polymers, respectively, including amine groups, carboxylic acid groups, hydroxyl groups, and perfluorinated alkyl chains. It was found that the heterofunctionalization should be carried out in the sequence of hydrosilylation and then thiol-ene reaction to achieve precisely defined products, probably due to the side products associated with the reaction between silyl hydrides and radical intermediates. The polymers have been thoroughly characterized by H-1 NMR, C-13 NMR, FT-IR, SEC, and MALDI-TOF mass spectrometry to establish their chemical structures and chain-end functionalities, which indicates precisely defined mono- and heterotelechelic polystyrenes with 100% functionalities. These polymers serve as important model compounds in the study of their bulk properties as well as self-assembling behaviors.