Synthesis of highly cross-linked polymers in supercritical carbon dioxide by heterogeneous polymerization

This paper reports the synthesis of highly cross-linked polymers in supercr itical CO2 (scCO(2)), both with and without the addition of a CO2-soluble d iblock copolymer stabilizer. It was demonstrated that, under certain specif ic conditions, relatively uniform, nonporous poly(divinylbenzene) (PDVB) mi crospheres (1-5 mu m diameter) can be generated in the absence of added sta bilizers. The effects of cross-linker ratio, monomer concentration, cross-l inker structure, and mechanical agitation were investigated. A CO2-soluble diblock copolymer stabilizer was synthesized using a modified screened anio nic polymerization (SAP) method. In the presence of this stabilizer (3% w/w ), much smaller PDVB microspheres (<0.5 mu m diameter) were formed, and it was shown that the particle size and particle size distribution were strong ly dependent on the stabilizer concentration. A range of cross-linked terpo lymers containing reactive or surface-active functional groups was generate d by heterogeneous copolymerization in scCO(2). Finally, these methods were extended to the synthesis of functional cross-linked microspheres containi ng an organic dye as a host molecule.