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

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.