Determination of the Intra- and Intermolecular Microstructure of Bulk and Emulsion Copolymers of Styrene and 2-Hydroxyethyl Methacrylate by Means of Proton NMR and Gradient Polymer Elution Chromatography

Abstract

A series of copolymers of styrene and 2-hydroxyethyl methacrylate was prepared with free-radical bulk copolymerization at 50 °C and analyzed with proton NMR to determine the reactivity ratios according to the terminal model and to study the intramolecular microstructure. The reactivity ratios were analyzed with a noniterative nonlinear least-squares method (r H = 0.48 ± 0.15 and rs = 0.27 ± 0.08) and the so-called error-in-variables method (r H = 0.49 and r s = 0.27). The hydroxyl proton resonance signal was found to be sensitive to the copolymer composition and could be interpreted in terms of compositional and configurational sequence effects. An assignment was proposed which is comparable to the assignments made for the methoxy protons of styrene-methyl acrylate copolymers. The coisotacticity parameter a H s was calculated using a nonlinear least-squares procedure with relative error estimation based on the current assignment and was found to be 0.33. With gradient polymer elution chromatography (chemical composition distribution) and with proton NMR, the inter- and intramolecular microstructures, respectively, of three emulsion copolymers of styrene and 2-hydroxyethyl methacrylate were studied. By using the chemical composition distribution and comparing the hydroxyl proton signal of these emulsion copolymers to that of a bulk copolymer with the same overall composition, it could be shown convincingly that styrene and 2-hydroxyethyl methacrylate copolymerize during the greater part of the emulsion polymerization.