Structure–chain length correlations in poly(N-vinylcarbazole)

Narrow molecular weight distribution samples of PVK have been prepared over the molecular weight (M_n) range of 3.7 × 10³ to 2.7 × 10⁶. No evidence of influence of the synthetic procedure on polymer tacticity has been observed. The glass-transition temperature T_g was linearly dependent on 1/M_n (T_g^∞ = 227°C) as predicted by the Fox-Flory chain-end free-volume model but no measurable change in free volume was detected. Crystallizability decreased with M_n and was zero in fractions below M_n = 46,000. This behavior coincides with that predicted by the nucleation theory outlined by Hoffman.²¹ This indicates that the chain-end free energy controls the stability of PVK folded-chain nuclei. The critical molecular weight for nucleation at 305°C was found to be some where in the range M_n = 1 ± 0.5 × 10⁵. No change in the structure of the folded-chain lamellae with M_n was observed but evidence was obtained to support adjacent reentry of chains and a resulting localized crystal distortion.