The effect of surfactant hydrophilic−lipophilic balance (HLB) on the catastrophic phase inversion of an emulsion, and the internal structure of the drops, was studied by using a model abnormal O/W/O emulsion. The system was composed of polyisobutylene, water, and a mixture of a water-soluble and an oil-soluble surfactant. The abnormal O/W/O emulsions were made by gradual addition of water to the oil in the presence of surfactant until the catastrophic phase inversion to the corresponding normal O/W emulsions occurred. The presence of an oil-soluble component in the surfactant, even in a low quantity, enhanced the stability of the abnormal W/O emulsion. The phase inversion was slightly advanced, in terms of water volume fraction, with decreasing HLB. Some indication was found that as the optimum HLB was approached, the inclusion of continuous phase into the dispersed phase increased. The size of internal oil droplets, which were entrained in the multiple water drops, was largely reduced with decreasing HLB as the optimum formulation was approached. The size of multiple water drops, which are dispersed in the continuous oil phase, however, showed a considerably smaller decrease with decreasing HLB. When, at a fixed oil/water ratio, the HLB of the abnormal emulsion approached that of the optimum, the catastrophic phase inversion to a corresponding normal emulsion occurred, indicating that abnormal emulsions cannot exist in the vicinity of the locus of transitional inversion.

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ABSTRACT:The heterogeneous polymerization of vinyl chloride monomer (VCM), with n-butane as the reaction medium, was used to prepare poly(vinyl chloride) (PVC) resins. The particle features of the resulting resins and the particle formation mechanism of the polymerization process were investigated. The PVC resins prepared by the new polymerization process had a volume-average particle size comparable to that of suspension PVC resins and a lower number-average particle size. From scanning electron micrographs, it could be seen that the new PVC resins had a regular particle shape and a smooth surface with no obvious skin. They also had a high porosity. The new PVC resins were composed of individual and loosely aggregated primary particles. The diameter of the primary particles in the top layer of the grains was smaller than that of the primary particles in the center part of the grains. On the basis of the particle features of these PVC resins, a particle formation mechanism for the new polymerization process was proposed. PVC chains precipitate from a VCM/n-butane mixed medium to form primary aggregates at a very low conversion, and the primary aggregates of the PVC chains aggregate to form primary particles, which further aggregate to form grains. The primary particles and grains grow by the capture of newly formed PVC chains and their primary aggregates and by polymerization occurring inside the aggregates.