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

This paper reports the synthesis of highly cross-linked polymers in supercritical CO2 (scCO(2)), 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 mu m 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 mu m 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 scCO(2). Finally, these methods were extended to the synthesis of functional cross-linked microspheres containing an organic dye as a host molecule.