Continuous polymerizations in supercritical carbon dioxide

We have developed a system for the continuous polymerization of various monomers in scCO(2) and the continuous removal of polymer particles from high-pressure to ambient conditions. Experiments have been performed with the surfactant-free precipitation polymerization of vinylidene fluoride (VF2) and acrylic acid (AA) utilizing diethyl peroxydicarbonate (DEPDC) as the free-radical initiator for VF2, and 2,2'-azobis(isobutyronitrile) (AIBN) as the free-radical initiator for AA. The PVDF and AA polymers were collected as dry, "free-flowing" powders. Tunable bimodal molecular weight distributions (MWDs) of poly(vinylidene fluoride) (PVDF) were achieved by varying the VF2 concentration. The conversion of VF2 in these polymerizations ranged from 7 to 26%, and the rate of polymerization (R-p) reached a maximum of 27 x 10(-5) mol/L(.)s at a VF2 feed monomer concentration of 2.5 mol/L at 75 degreesC. Homogeneous free-radical kinetics provided a good approximation for the rate of polymerization (Rp) of this heterogeneous polymerization. The PVDF material was characterized by gel permeation chromatography (GPC) and melt flow index (MFI) giving M-w's up to 104 kg/mol, and MFI's as low as 3.0 at 230 degreesC.