Glass transition temperature and melting temperature of uniform isotactic and syndiotactic poly(methyl methacrylate)s from 13mer to 50mer

Abstract

Highly isotactic (it-) and highly syndiotactic (st-) poly(methyl methacrylate)s (PMMAs) were fractionated into the individual homologues (uniform polymers) from the 13mer to the 50mer by means of supercritical fluid chromatography. The glass transition temperature ( T g) and crystalline melting temperature of the uniform PMMA samples were determined by differential scanning calorimetry. The T g values of the uniform PMMAs were higher than those of the non-uniform PMMAs which are equivalent to the uniform PMMAs in tacticity, number-average molecular weight, and end-group structure. Over the molecular weight range from 1359.6 (13mer) to 5064.0 (50mer), plots of T g against the reciprocal molecular weight ( M −1) are well fitted by a linear relationship: T g (C)= (49.6±1.3)−(4.34±0.26) × 10 4 M −1 for the uniform it PMMAs and T g (C)=(123.3±1.7)−(9.38±0.33)×10 4 M −1 for the uniform st PMMAs with a degree of polymerization (DP)≥28 crystallized from its methanol solution by evaporation of the solvent. The reciprocal equilibrium melting temperature ( T m −1) of the crystalline uniform it PMMAs increased linearly with increasing DP −1. Extrapolation of the linear relationship gave the T m of it-PMMA at infinite DP as 171.1 C.