GLASS-TRANSITION TEMPERATURE AND MELTING TEMPERATURE OF UNIFORM ISOTACTIC AND SYNDIOTACTIC POLY(METHYL METHACRYLATE)S FROM 13MER TO 50MER

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) (degree-C) = (49.6 +/- 1.3)-(4.34 +/- 0.26) x 10(4) M-1 for the uniform it-PMMAs and T(g)(degree-C)=(123.3 +/- 1.7) - (9.38 +/- 0.33) x 10(4) M-1 for the uniform st-PMMAs. Each uniform it-PMMA with a degree of polymerization (DP) greater-than-or-equal-to 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.