Particle size and molecular weight distributions of various polystyrene emulsions

Abstract

Abstract Three different emulsion polymerization techniques, the batch (B), monomer addition (M Add), and emulsion addition (E Add) procedures were studied. Rates of polymerization indicated that the B reacted more rapidly than either the M Add or E Add. This was related to the lower monomer concentration present in the M Add and E Add systems. This is described as monomer starvation. MW and MW distributions were compared for these polymers. The B polymer had a significantly higher MW than either the M Add or E Add polymer. This could also be related to monomer starvation in the latter systems. However, the MW distribution of these polymers gave comparable values of M w /M n = 3.1. This indicates a similar molecular growth phenomena which appears to result from polymerization occurring near the particle surface for the addition systems. Particle size distribution measurements showed the B latex to have the narrowest distribution while the E Add latex had the widest. Also, the M Add had a particle diameter distribution which was approximated by a normal distribution. This is explained by use of the monomer starvation concept. Additional polymerizations were carried out called “hybrids” which were variations of the polymerizations discussed above. Significant differences result from the various techniques of emulsion polymerization. These differences manifest themselves not only in average particle size and MW, but also in particle size distribution. No significant differences were obtained in MW distributions.