Ai. Cooper et al., Synthesis of highly cross-linked polymers in supercritical carbon dioxide by heterogeneous polymerization, MACROMOLEC, 32(7), 1999, pp. 2156-2166
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.