Surfactant Assisted Polymerization of Tetrafluoroethylene in Supercritical Carbon Dioxide with a Pilot Scale Batch Reactor.

Abstract

Chain-free radical polymerization of tetrafluoroethylene (TFE) was carried out in supercritical carbon dioxide (scCO(2)), at 50 degrees C and 121-133 bar, with tertiary-amyl-per-pivalate as a free radical initiator, using a 5-L pilot scale batch reactor. Experiments were carried out both in the absence and in the presence of perfluoropolyether (PFPE) carboxylate surfactants. Stabilizers were employed under the free acid form and as sodium and calcium salts. An expanded fibrillated poly(TFE) was obtained in all experiments. In the case of surfactant-free polymerizations, the product was mainly constituted by irregular shape macroparticles having size in the range 200-500 pm. Quite interestingly, when the free acid surfactant was used, a clear acceleration of the polymerization rate was observed and smaller polymer particles with more regular quasi-spherical morphology were obtained. Melt fusion crystallinity of as-polymerized poly(TFE) seemed not substantially affected by the presence of the stabilizers and was rather high (80-86%) suggesting that polymerization mainly occurs at polymer particle surface. All these elements suggest that FLUOROLINK(R) 7004H PFPE carboxylic acid decreases coagulation of primary polymer particles leading to an increase in polymer surface area.