Amphiphilic Block Copolymers as Stabilizers in Emulsion Polymerization: Effects of the Stabilizing Block Molecular Weight Dispersity on Stabilization Performance

Molecular weight dispersity is not typically studied as a design parameter of block copolymer stabilizers but is often assumed to impact stabilization performance; low molecular weight dispersity is generally assumed to be associated with best performance. This is the first quantitative investigation of the effects of block copolymer molecular weight dispersity with regards to stabilization performance in an emulsion polymerization. Poly­(styrene)-<i>b</i>-poly­(acrylic acid) block copolymers were synthesized by nitroxide-mediated radical polymerization and employed as stabilizers in the emulsion polymerization of styrene. The effect of the stabilizing poly­(acrylic acid) block molecular weight dispersity on stabilization behavior was studied, independent of molecular weight and composition. Block copolymer stabilizers were evaluated in terms of critical aggregation concentration, dispersed phase particle size, distribution, and zeta potential. The molecular weight dispersity of the stabilizing block affected the aggregation number and final number of particles but displayed no negative effects on stability or size distribution