Chemical heterogeneity analysis of high-conversion poly[styrene-co-(ethyl acrylate)]s by NMR and on-line coupled SEC-NMR

Copolymers of styrene and ethyl acrylate are prepared by radical polymeriza tion and analysed with respect to microstructure by means of nuclear magnet ic resonance. Using C-13 NMR, the compositional styrene- and ethyl acrylate -centered triads can be determined and compared to theoretical values. Good agreement between experimental and calculated triad concentrations are obt ained for styrene-rich copolymers. Ethyl acrylate-rich copolymers exhibit s ignificant deviations from the calculated values in particular for the ethy l acrylate homotriads. Using on-line coupled SEC-H-1 NMR, the chemical comp osition across the molar mass axis can be monitored. It is found that ethyl acrylate-rich copolymers exhibit a broader molar mass and chemical composi tion distribution than styrene-rich copolymers, The results indicate that t he block character of the copolymers with respect to ethyl acrylate units i ncreases with increasing molar mass.