Microgel stars viaReversible Addition Fragmentation Chain Transfer (RAFT) polymerisation — a facile route to macroporous membranes, honeycomb patterned thin films and inverse opal substrates

Arm first microgel polymers were successfully synthesised utilising Reversible Addition Fragmentation Chain Transfer (RAFT) polymerisation techniques. A functional prearm linear AB block copolymer intermediate, (polystyrene)-block-(polydivinylbenzene), was prepared via RAFT by simple one pot chain extension and arm coupling of a preprepared polystyrene macromer. The arms are coupled together via the residual unsaturation present in the polydivinylbenzene block by free radical means to form core-crosslinked microgels. It was found that the arm coupling process could be described by invoking a two-stage coupling system. The initial induction period consists of the formation of largely two-arm (on average) species. This is followed by a latter growth period, where true core-crosslinked microgels are formed consisting of polyarm clusters having 16 arms (on average) per cluster. These microgel materials were cast under specific conditions to form porous polymer films of varying quality. Image analysis of these films demonstrated the importance of the linear component : microgel component ratio in determining both a uniform pore size and the formation of a hexagonal close packed array of pores.