All-aqueous continuous-flow RAFT dispersion polymerisation for efficient preparation of diblock copolymer spheres, worms and vesicles
We report the scalable, all-aqueous synthesis of poly(dimethylacrylamide)–poly(diacetone acrylamide) (PDMAm–PDAAm) diblock copolymer spheres, worms and vesicles by reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerisation in a low-cost continuous-flow (CF) reactor. A transient state kinetic profiling method using a 5 mL reactor coil indicated a considerably faster rate than the equivalent batch reaction. Higher throughput was subsequently demonstrated by employing a 20 mL coil reactor for the synthesis of a 135 g, 30% w/w batch of PDMAm113 macromolecular chain transfer agent (macro-CTA) at 98% conversion. This was used without further purification to polymerise DAAm in a CF reactor. During this polymerisation, the chains underwent polymerisation-induced self-assembly (PISA) producing block copolymer spheres. This reaction also proceeded faster than in batch, and the high resolution kinetics enabled clear observation of the rate enhancement which is characteristic of PISA systems. GPC studies indicated the formation of a copolymer with low molar mass dispersity and complete blocking efficiency, despite the high conversion achieved during the precursor macro-CTA synthesis. It was subsequently demonstrated that the PDMAm113 macro-CTA could be used to prepare PDMAm113–PDAAmx block copolymer spheres (where x = 50, 100 and 200) with systematically increasing particle diameters. Finally, by reducing the PDMAm macro-CTA DP to 50 and increasing total solids to 20% w/w, it was possible to prepare worms and vesicles in the tubular reactor by tailoring the residence time to achieve specific degrees of polymerisation of the PDAAm block.