DROP COALESCENCE PROCESSES IN SUSPENSION POLYMERIZATION OF VINYL-CHLORIDE

A tracer dye technique was used to investigate the effect of turbulenc e intensity, stirring time, and the type and concentration of the susp ending agent, partially hydrolyzed poly(vinyl acetate) (PVA), on the c oalescence rate of vinyl chloride monomer (VCM) droplets in an agitate d liquid-liquid dispersion. It was found that the extent of coalescenc e rises slowly with mixing time, is roughly proportional to the agitat ion speed, and decreases sharply when the concentration of stabilizer is increased. Coalescence rate depended on the degree of hydrolysis of the stabilizer. The method of addition of initiator during VC suspens ion polymerization was also studied and its effects on the polymerizat ion conversion and final PVC particles' properties were determined. It was found that the polymerization reaction occurs more uniformly in a ll the VCM droplets when the initiator was predissolved in the VCM pri or to reaction compared with the case when the initiator was predisper sed in the continuous water phase. Also, for the same reaction time, t he conversion was higher in the former case. During polymerization, th e concentration of PVA in the aqueous phase decreased substantially an d the porosity of the polymer particles was reduced. (C) 1996 John Wil ey & Sons, Inc.