Characterization of Poly (styrene-co-acrylonitrile) s by Light Scattering

Weight-average molecular weights (Mw) and second virial coefficients (A2) of poly (styrene-co-acrylonitrile) s (AS) were measured using a laser light scattering photometer. The Mw's determined by GPC in tetrahydrofuran (THF) agreed well with those determined with light scattering within experimental errors, when the copolymer molecular weights'relative to polystyrene' by GPC were calculated assuming that molecules of equal contour chain length appear at equal GPC elution volumes. The Mw's determined in DMF solution were in disagreement with those determined with light scattering. Mw (GPC) /Mw increased linearly with an increase in acrylonitrile content of AS. The A2 for AS in THF was a concative function of copolymer composition, and the maximum was observed at around 30 to 40 mol% of acrylonitrile. However, compositional dependence of the A2 was very weak, and the solvent power of THF for each AS appears to be practically the same. This may be the reason why Mw's by GPC agreed with those by light scattering. On the other hand, the A2 in N, N-dimethylformamide (DMF) increased with increasing acrylonitrile content. From the A2 values it is concluded that the copolymer chains in DMF are more expanded than polystyrene chains.