The dependence of the glass transition temperature of poly(<i>N</i>‐vinylcarbazole) upon steric microstructure and molecular weight

Abstract

Abstract Poly( N ‐vinylcarbazole) (PVK) samples were found to exhibit up to three glass transition temperatures T g , corresponding to the whole chain and the syndiotactic and isotactic stereoblocks. An increasing tendency to multiple T g s, and hence to phase separation, was observed with increasing isotacticity. Limiting values at infinite molecular weight for syndiotactic and isotactic PVK were obtained from correlations of the T g s corresponding to the syndiotactic and isotactic stereoblocks with their respective average stereoblock lengths derived from 13 C NMR measurements. They were found to be 549 and 399 K, respectively. The conventional T g for PVK was found to exhibit the following dependence upon the syndiotactic dyad mole fraction X s : The molecular weight dependences of the conventional T g s for several fractionated PVK samples obeyed a Fox–Flory‐type relation with values of − dT g / d (1/ M ) varying between 7.6 × 10 3 for isotactic PVK and 2.7 × 10 5 for Luvican M 170.