Synthesis of block copolymers by the conversion of living anionic polymerisation into living ROMP

Abstract

A methodology for the synthesis of well-defined block copolymers from living anionic polymerisation and ring opening metathesis polymerisation (ROMP) using well-defined ruthenium alkylidene initiators has been developed. Polymers synthesised by anionic polymerisation were converted into macromonomers, which were used as precursor polymers to well-defined ruthenium macroinitiators for ROMP. The macroinitiators were synthesised by an olefin metathesis reaction, involving alkylidene exchange of Ru(Cl(_2)(=CHEt)(PCy(_3))(_2) with the macromonomers. The ROMP of norbornene (NBE) derivatives using the macroinitiators resulted in the synthesis of block copolymers. These copolymers possessed low polydispersity indices (typically 1.2 or less) and contained small quantities or none of the anionically polymerised homopolymer.Poly(ethylene oxide) (PEO) macromonomers were synthesised by terminating living PEO with 4-vinylbenzyl chloride. The PEO macromonomers were used to synthesise block copolymers of ethylene oxide (EO) and NBE derivatives. Polystyrene (PS) macromonomers were prepared by Williamson coupling of hydroxyl functionalised PS and 4-VBC. The hydroxyl functionalised PS was synthesised by end functionalising living PS with EO or by incorporating a hydroxy functionality into the initiator in a protected form. Copolymers of styrene and NBE derivatives were produced using the PS macromonomers. The applicability of this methodology to other monomers that can be polymerised by an anionic mechanism was examined. The ROMP monomers included NBE derivatives with imide, dicarboxylic ester and chloromethyl groups, illustrating the range of functionalities that can be incorporated into the ROMP block using this methodology.