Molar-mass chemical-composition distributions of styrene-methyl acrylate copolymers prepared by solution or emulsion polymerization

The microstructure of copolymers can be characterized in terms of triad fractions and tacticity parameters (i.e. intramol. structure), and in terms of a 3-dimensional molar-mass chem.-compn. distribution (MMCCD) (i.e. intermol. structure). The microstructure obtained is controlled by the copolymn. conditions, for instance by the choice of the reaction system (homogeneous soln. or heterogeneous emulsion), the degree of conversion, and the choice of reactants. Computer simulations of emulsion copolymn., accounting for the main chem. and phys. processes, provide MMCCD predictions of emulsion copolymers. These MMCCDs are calcd. by considering the conversion heterogeneity (compn. drift) as well as the instantaneous (statistical) compn. distribution of the copolymers formed. Cross-fractionation (2-dimensional chromatog.) was used to verify the predicted MMCCDs of the copolymer products. The copolymers are sepd. according to molar mass by means of size exclusion chromatog. (SEC), and each SEC fraction is subsequently analyzed according the chem. compn. by means of gradient elution quant. thin-layer chromatog./flame ionization detection. The difference in water soly. of the 2 monomers (styrene and Me acrylate) appears to be one of the major factors detg. the microstructure of the copolymers. Depending on conversion, monomer ratio, and monomer-to-water ratio, the model predicts either single- or double-peaked MMCCDs, in full agreement with the exptl. obtained distribution