William P. Hems's research while affiliated with University of Cambridge and other places

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Application of the ‘screened anionic polymerisation’ method to the synthesis of well-defined AB block copolymers derived from methyl methacrylate and fluorinated methacrylate monomers has provided a family of tuneable surfactants for the free radical dispersion polymerisation of methyl methacrylate in supercritical carbon dioxide. Poly(methyl methacrylate) is obtained with excellent conversion and high molecular weight. Block copolymers having higher molecular weight and higher fluorine contents are superior surfactants, and by systematic evaluation of the parameters in the dispersion polymerisation of methyl methacrylate, discrete polymer particles can be obtained.

This paper reports the synthesis of highly cross-linked polymers in supercritical CO2 (scCO2), both with and without the addition of a CO2-soluble diblock copolymer stabilizer. It was demonstrated that, under certain specific conditions, relatively uniform, nonporous poly(divinylbenzene) (PDVB) microspheres (1−5 μm diameter) can be generated in the absence of added stabilizers. The effects of cross-linker ratio, monomer concentration, cross-linker structure, and mechanical agitation were investigated. A CO2-soluble diblock copolymer stabilizer was synthesized using a modified screened anionic polymerization (SAP) method. In the presence of this stabilizer (3% w/w), much smaller PDVB microspheres (<0.5 μm diameter) were formed, and it was shown that the particle size and particle size distribution were strongly dependent on the stabilizer concentration. A range of cross-linked terpolymers containing reactive or surface-active functional groups was generated by heterogeneous copolymerization in scCO2. Finally, these methods were extended to the synthesis of functional cross-linked microspheres containing an organic dye as a host molecule.

The intramolecular 1,3-dipolar cycloaddition reactions of (Z)-N-4-alkenylnitrones carrying various alkenyl substituents were investigated, and the regiochemistry of the resulting isoxazolidines was determined. Silyl- and bromo-substituents were found to effect significant regiocontrol on the intramolecular nitrone dipolar cycloaddition reaction.

Herein we report the synthesis of highly cross-linked polymers based on divinylbenzene by heterogeneous polymerization in supercritical CO2 (scCO2). The polymers were isolated in the form of discrete microspheres (diameter = 1.5–5 μm) in good yields (≥90%), in the absence of any stabilizers. In the presence of a CO2-soluble polymeric stabilizer, much smaller particles (diameter <0.5 μm) were formed in high yields (≥95%) by emulsion polymerization in scCO2.

Herein we report the synthesis of highly cross-linked polymers based on divinylbenzene by heterogeneous polymerization in supercritical CO2 (scCO(2)). The polymers were isolated in the form of discrete microspheres (diameter = 1.5-5 mu m) in good yields (greater than or equal to 90%), in the absence of any stabilizers. In the presence of a CO2-soluble polymeric stabilizer, much smaller particles (diameter < 0.5 mu m) were formed in high yields (greater than or equal to 95%) by emulsion polymerization in scCO(2).

Screened anionic copolymerisation of methyl methacrylate with the perfluoroalkyl methacrylates 2 affords well-defined AB block copolymers 4–6, which serve as effective surfactants in the dispersion polymerisation of methyl methacrylate in supercritical carbon dioxide.