Direct synthesis via RAFT of amphiphilic diblock polyelectrolytes facilitated by the use of a polymerizable ionic liquid as a monomer

Abstract

A new method for obtaining amphiphilic block polyelectrolytes with a strongly hydrophobic block under homogeneous conditions is described and demonstrated by synthesizing poly(2-acrylamido-2-methanepropanesulfonate-b-styrene) block copolymers using RAFT polymerization. The technique involves the transformation of the 2-acrylamido-2-methanepropanesulfonate (AMPS) monomer into a polymerizable ionic liquid (PIL) by neutralization with triethylamine, which renders the resulting P(Et₃N-AMPS) macroCTA soluble in DMF, DMSO, and ethanol. Consequently, straightforward homogeneous chain extension with a strongly hydrophobic monomer such as styrene is possible under homogeneous conditions. Homopolymerization of the PIL monomer is studied, revealing pseudo-1^st-order kinetics and polydispersities slightly higher than those for the Na-AMPS monomer. High end group fidelity is demonstrated by chain extension experiments. Amphiphilic diblock copolymers are synthesized in a range of targeted chain compositions, and their formation is confirmed by SEC and ¹H-DOSY, and by investigating self-assembled structures with DLS. The reverse approach based on styrene-first polymerization also proved successful, further expanding the scope of this work. We believe that this provides an interesting alternative to protection–deprotection methods and emulsion polymerization methods, when strongly anionic block copolymers are desired.