Synthesis of CO2-responsive gradient copolymers by switchable RAFT polymerization and their controlled self-assembly

Abstract

Switchable reversible addition–fragmentation chain-transfer (RAFT) agents, so-called because they can be reversibly switched by an acid/base stimulus to offer very good control over polymerization of both “more-activated” monomers (MAMs) and “less-activated” monomers (LAMs), provide a route to prepare well-defined polyMAM-block-polyLAM copolymers. This paper presents ¹H NMR studies in determining the effect of the type and amount of acid on the efficiency of the protonation of a switchable RAFT agent. Acid type and concentration have a marked effect on the degree of control over switchable RAFT polymerization. Best control was achieved with a stoichiometric amount of the strongest acid investigated, trifluoromethanesulfonic acid. In addition, we describe a facile synthesis of the well-defined CO₂-responsive gradient copolymers poly(benzyl methacrylate)-block-(poly(N,N-diethylaminoethyl methacrylate)-gradient-poly(N-vinylpyrrolidone))-block-poly(N-vinylpyrrolidone) (PBzMA-b-P(DEAEMA-grad-NVP)-b-PNVP) through switchable RAFT polymerization. The amphiphilic gradient copolymers can self-assemble to form various multicompartment micelles in selective solvents, and the assembled micelles widely possess patchy, noncontinuous subdomains around the inner micelle cores. Through CO₂ stimulation, their inhomogeneous nature will endow the gradient copolymers with some different stimuli-responsive factors from those of block copolymers, which emerged with obviously heterogeneous and compartmentalized shell nanodomains. Furthermore, this gradient strategy may offer a new way to design and realize precise morphological manipulation.