Semicontinuous emulsion copolymerization to obtain styrene-methyl acrylate copolymers with predetermined chemical composition distributions

Four types of emulsion copolymerization processes were applied to produce various styrene–methyl acrylate copolymer latices. (1) Batch emulsion copolymerization. (2) Monomer starved semicontinuous emulsion copolymerization, i.e., a monomer mixture of constant composition was fed to the reactor at a constant rate. Sufficiently low addition rates led to homogeneous copolymers. (3) Optimal addition rate profiles were used to produce homogeneous emulsion copolymers in relatively short times. The profiles were determined in a semiempirical way, and applied to three different copolymer compositions. (4) We made an attempt to determine an addition rate profile to produce a heterogeneous emulsion copolymer with predetermined heterogeneity, i.e., a copolymer of which the chemical composition distribution (CCD) did not consist of one narrow peak, as with homogeneous copolymers, but had a predetermined broadness profile. Strategies (2) and (3) were used to produce homogeneous emulsion copolymers with varying fractions of styrene. Strategy (3) was also used to demonstrate the influence of the monomer ratio on the kinetics. The advantage of this method is that the monomer ratio is constant over the whole conversion range in the latex particles. High performance liquid chromatography (HPLC) was used to determine the homogeneity/heterogeneity of the copolymers produced, and proved to be invaluable in determining the optimal addition rate profile. The final goal will be to study the influence of the chemical composition distribution (CCD) on mechanical properties of these copolymers, as both homopolymers used in this study have quite differentglass transition temperatures; the results will be published later. © 1993 John Wiley & Sons, Inc.