Seeded semibatch emulsion copolymerization of methyl methacrylate and butyl acrylate using polyurethane dispersion: effect of soft segment length on kinetics

Abstract

Aqueous acrylic–polyurethane (AC–PU) hybrid emulsions were prepared by semibatch emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA) in the presence of two polyurethane (PU) dispersions. PU dispersions were synthesized using isophorone diisocyanate (IPDI), 1000 or 2000 molecular weight poly(neopentyl)adipate, and dimethylol propionic acid (DMPA). The monomer mixture was added in the monomer emulsion feed. We studied the effect of PU chain rigidity on the rate of polymerization, the particle size and distribution, the number of particles, and the average number of radicals per particle. The rigidity was controlled by varying the molecular weight (Mn) of the polyol, which represents the soft chain segment. The monomer feed rate was varied in order to study its influence on the process. It was observed that PU particles, prepared with higher molecular weight polyol, swelled to a greater extent with acrylic (AC) component. In the pseudo steady state the polymerization rate acquired a constant value, comparable to the value of monomer addition rate. The total particle number in the reactor in the pseudo steady state was constant and similar to the number of PU particles in the initial charge. The obtained results suggested that the MMA/BA copolymerization in the presence of PU seeds showed intermediate behavior between Smith-Ewart cases I and II.