Preparation and properties of isotactic and syndiotactic poly(methyl methacrylate)s, uniform with respect to molecular weight

Abstract

AbstractHighly isotactic (it‐) and highly syndiotactic (st‐) poly(methyl methacrylate)s (PMMAs) uniform with respect to molecular weight (stereoregular, uniform PMMAs) were isolated up to the 100mer from it‐ and st‐PMMAs by supercritical fluid chromatography (SFC) and characterized by NMR and mass spectroscopies. Glass transition temperatures (Tg's) of the uniform it‐ and st‐PMMAs were higher than those of the corresponding PMMAs with MWD and with similar molecular weight on average. The Tg values of the uniform it‐and st‐PMMAs series obeyed the relationship, Tg = Tg∞ ‐ K/M, where M and Tg∞ denote molecular weight and Tg at infinite M, respectively. The reciprocal melting points (1/Tm) of uniform it‐PMMA (degree of polymerization, DP = 28–44), obtained from methanol solutions by evaporating the solvent, increased linearly with increasing 1/DP. Extrapolation of the linear relation to 1/DP = 0 gave the Tm of it‐PMMA with infinite DP; Tm∞ = 171.1°C. Thermal degradation behavior was studied by thermogravimetry and by SFC analysis of degradation products. In gel‐permeation chromatography (GPC) measurements, the it‐50mer eluted faster than the st‐50mer. Calibration curves for it‐ and st‐PMMAs could be obtained using series of the uniform PMMAs. The instrumental spreading factor determined using it‐25mer, it‐50mer, st‐25mer and st‐50mer for our GPC chromatograph was 0.070 ml when the volume of the sample solution was 0.003ml. GPC analysis of a mixture of the it‐ and st‐50mers in tetrahydrofuran indicated formation of a stereocomplex in the solution, and was found quite useful to elucidate the minimum sequence length required for complex formation.