Phase separation in random copolymers from high conversion free radical polymerization, 2 Chemical heterogeneity analysis of poly(styrene-co-ethyl acrylate) by gradient HPLC

摘要

Copolymers of styrene and ethyl acrylate are prepared by radical copolymerization and analysed with respect to chemical composition distribution. By gradient HPLC using a reversed stationary phase and tetrahydrofuran-acetonitrile as the mobile phase, the copolymers are separated with respect to chemical composition in the order of increasing styrene content. For the samples under investigation, the molar mass does not affect the separation. Quantitative information on the chemical heterogeneity is obtained by calibrating the chromatographic system with chemically narrow-distributed low-conversion copolymers. In agreement with the theory it is found that for high-conversion samples the chemical heterogeneity increases with increasing content of ethyl acrylate in the copolymer. The HPLC separation mechanism is discussed in terms of precipitation and adsorption effects.