Synthesis of pH-responsive brush copolymers by raft polymerisation and click chemistry reactions

Abstract

In this study, anionic brush copolymers were synthesised by grafting onto strategy, combining radical addition fragmentation chain transfer (RAFT) polymerisation and two click chemistry reactions, namely, epoxy–thiol and azide–alkyne. The backbone of the prospective brush copolymers with multiple epoxy groups and the nearly equimolar composition of the monomeric units was synthesised by RAFT copolymerisation of butyl methacrylate (BMA) and glycidyl methacrylate (GMA). Poly(tert-butyl methacrylate) (p(t-BMA) as a precursor for the side chains was synthesised by RAFT polymerisation and, subject to the structure of the chain transfer agent, contained terminal thiol or alkyne groups. The course of the click reactions was monitored by DLS. Anionic brush copolymers containing carboxyl groups were obtained via acidic hydrolysis of t-BMA units.
Aqueous solutions of the anionic brush copolymers were studied by potentiometric and turbidimetric titration, and by DLS. Both anionic brush copolymers, irrespective of the type of click chemistry reaction, were weak polyacids. Anionic brush copolymers, synthesised by the epoxy–thiol click reaction, form rather compact aggregates, whereas those, synthesised by the azide–alkyne click reaction, assemble into larger microgel-like aggregates. In the synthesis of brush copolymers, the method of epoxy–thiol click chemistry has some advantages because of simpler experimental procedures and higher grafting density in the products.