John F. Quinn

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.

Reversible addition-fragmentation chain transfer polymerization initiated with γ-radiation at ambient temperature: an overview

Using gamma-radiation as initiation source at ambient temperatures (i.e. T approximate to 20 degreesC) for reversible addition-fragmentation chain transfer (RAFT) polymerizations allows for the generation of narrowly distributed polymeric material with living characteristics. It is shown that the living characteristics effected by RAFT agent mediated bulk polymerizations using gamma-irradiation are associated with a RAFT mechanism rather than with reversible termination processes. Furthermore, gamma-radiation as initiation source for an appropriate RAFT agent/monomer system allows for effective radical storage and the generation of long-lived reaction intermediates at ambient temperatures. The current overview further demonstrates how the RAFT process together with gamma-radiation as source of initiation can be employed to graft various monomers onto polypropylene surfaces in a controlled manner

Living Free Radical Polymerisation Under a Constant Source of Gamma Radiation – An Example of Reversible Addition-Fragmentation Chain Transfer or Reversible Termination?

The primary mechanism for living polymerisation under a source of gamma radiation at low dose rates is shown to be reversible addition-fragmentation chain transfer. This was demonstrated by showing that the initial transfer step determines the success of the polymerisation. When an inappropriate leaving group is chosen for the RAFT agent, the polymerisation is non-living. Under a reversible termination mechanism the living-ness should be independent of this initial transfer step.

Ambient temperature reversible addition–fragmentation chain transfer polymerisation

Reversible addition fragmentation chain transfer was performed nat ambient temperature for the first time.

Molecular weight fractionation of poly(methyl methacrylate) using Gas Anti-Solvent techniques

The solubility of poly(methyl methacrylate) in acetone, expanded by carbon dioxide, was studied at 20 °C for a variety of molecular weights and architectures. The suitability of the Gas Anti-Solvent method for fractionation of poly(methyl methacrylate) was investigated with positive results. The threshold pressure for precipitation of various monodisperse molecular weights was investigated, and the effectiveness of this technique to fractionate a polymer with a broad molecular weight distribution was evaluated. The pressure required to precipitate polymers was found to be low, generally below 60 bar.