Particle morphology in the radiation‐induced heterophase polymerization of vinyl chloride with solvent added in small amounts

Abstract

AbstractInvestigations were carried out on the polymer particle morphology obtained in the early stages of radiation‐induced bulk polymerization of vinyl chloride with solvent added in small amounts over the temperature range of −10 to 70°C under quiescent conditions. At low temperatures, when the polymerization is carried out in the absence of solvent, there is flocculation of irregular aggregates of two types depending on polymerization conditions: (i) small primary particles that remain finely dispersed and (ii) large flocs that undergo rapid sedimentation. By addition of increasing amounts of solvent a gradual change towards single small spherical particles that remain finely dispersed is obtained. With more than 3% w/w THF, spherical particles in latexlike dispersions are obtained in polymerizations at −10 and 22.8°C, and show a small change in size with increasing amounts of THF. In the high‐temperature range, 50–70°C, where spherical particles can be obtained in the absence of solvent, no significant changes are produced by addition of THF. The results are discussed in the terms of a marked increase in particle plasticization by the solvent, enabling the coalescence of flocculated particles of small size to occur also in polymerization at low temperature.