Surfactant effects in polytetrafluoroethylene dispersion polymerization

Abstract

The polymerization rate, surfactant adsorption behaviour and polymer particle morphology are significantly affected by initial surfactant concentration and polymerization time in the aqueous dispersion polymerization of tetrafluoroethylene. The surfactants are lithium perfluoroalkanoates (CF 3(CF 2) n CO 2Li, n = 5−8). Both hexagonally shaped and short rod-like particles are formed in early stages of the polymerization when the initial surfactant concentration is below its critical micelle concentration (c.m.c.) An increase in the surfactant chain length and concentration tends to promote formation of hexagons. At longer polymerization times, roughly spherical particles, called cobblestones, form the dominant population. As the initial surfactant concentration is increased past its c.m.c., rod-like particles become the dominant population, with the aspect ratio of the rods increasing as the surfactant concentration increases. As previously reported, the rod-like particles and hexagons are single crystals and dispersions of exclusively rod-like particles can form a separate anisotropic phase.