MECHANISM OF THE EMULSION PRECIPITATION POLYMERIZATION OF CHLOROTRIFLUORETHYLENE .1. KINETICS OF THE POLYMERIZATION

Emulsion polymerizations of chlorotrifluoroethylene (CTFE) were performed employing ammonium persulfate as initiator and ammonium perfluorooctanoate as surfactant. The polymerization showed a pseudo-zero-order dependence on monomer concentration throughout 80% of the reaction. Increasing the initiator concentration produced faster polymerization rates and larger particle number densities, while the rate of polymerization per particle decreased slightly. The increase in the number of latex particles with increasing initiator concentration provided additional sites for the polymerization to occur, causing a lower radical entry rate and a lowering of the per particle rate of polymerization. This phenomenon of the polymerization accounted for the observed high initiator concentration rate order dependence (0.8) and the constancy of molecular weight with initiator concentration. Increases in surfactant concentration also increased the polymerization rate by increasing the particle number density. However, the rate per particle decreased by a factor of 40 with surfactant concentration which was most likely due to a decrease in the number of free radicals per particle in the smaller volume latex particles. Molecular weights of the polymers (PCTFE) were independent of the radical concentration within the particles but varied inversely with polymerization temperature. Molecular weight is believed to be controlled either by chain transfer to monomer or by a highly temperature-dependent termination process for the occluded radicals. This study revealed that the presence of occluded radicals in the polymer matrix accounts for many of the unexpected observed experimental results. Isolation of the radicals, in the emulsion-precipitation polymerization of CTFE, occurs not only among latex particles but also within the particles themselves.