Continuous polymerizations in supercritical carbon dioxide: Chain-growth precipitation polymerizations

A continuous process for the precipitation polymerization of various monomers in supercritical carbon dioxide was studied. Experiments were performed mainly with the surfactant-free precipitation polymerization of vinylidene fluoride (VF2) and acrylic acid (AA) utilizing diethyl peroxydicarbonate as the free-radical initiator for VF2 and 2,2′-azobis(isobutyronitrile) as the free-radical initiator for AA. The experiment was performed at 75 °C temperature, 275 bar pressure, and at 15 to 45 min residence time. The polymer was collected as a dry `free-flowing' powder and was characterized by gel permeation chromatography.