Copolymer composition control by means of semicontinuous emulsion copolymerization

The effect of 2 different monomer addn. strategies on the chem. compn. distribution of the copolymer formed by the (seeded) semicontinuous emulsion copolymn. of styrene and Me acrylate is investigated. The addn. of a mixt. of the monomers at a const. feed rate results in a homogeneous copolymer, provided that extremely long process times are used (starved conditions). When not starting from a seed latex, aq. phase polymn. is obsd. at low feeding rates. When using a seed latex, aq. phase polymn. appears to be negligible. An optimal monomer addn. profile is calcd. from accurate monomer partitioning data using a short iteration procedure. Gradient high-performance liq. chromatog. (HPLC) is successfully applied as a rigorous test of the homogeneity of the copolymer formed. The information obtained contains much more detail than in the case of using DSC or 1H NMR. 1H NMR provides only av. cumulative chem. compns.; the complete chem. compn. distribution can be obtained by means of HPL