A Dispersion Polymerization System with Nuclei Distinguishable from Polymer Particles

Abstract

A dispersion polymerization is described wherein the nuclei are distinguished from polymer particles. Specifically, it has been observed that dispersion polymerization of pyrrole using FeCl3 oxidant in pure or 70% ethanol yields dispersions with two kinds of particles: (i) nanoparticles of <20 nm diameter which comprise 1−2% of the total particle mass; (ii) particles ca. 10 times as large in diameter. These results have been explained in light of particle nucleation and stabilization concept provided by Paine. While the nanoparticles continue to be present althrough the polymerization, the size of the bigger particles increases almost linearly with conversion (measured over the range 8−92%). This result indicates that no new particles are formed after the primary stabilization process is over and the particles grow by absorption of small particles (heterocoalescence). The nanoparticles are identified as nuclei and small aggregates of nuclei (particulates) and the bigger particles as the stabilized polymer particles. The nuclei or the particulates in this particular case happen to be metastable. With a change of the medium of polymerization to water, the nanoparticles disappear; i.e., the nuclei becomes unstable. The very fast rate of polymerization encountered in the latter case presumably results in a failure of the rate of stabilizer adsorption to cope with the rate of nucleation so that the nuclei become unstable and therefore not observed in transmission electron microscopy pictures.