Investigations of poly(vinyl alcohol)/poly(<i>N</i>‐vinyl‐2‐pyrrolidone) blends, 2. Influence of the molecular weights of the polymer components on crystallization

Abstract

Abstract Blends of crystallizable poly(vinyl alcohol) (PVA) and poly‐( N ‐vinyl‐2‐pyrrolidone) (PVP) of different molecular weights were prepared from aqueous solutions by evaporation and studied by Fourier‐transform IR spectroscopy. When the molecular weight of one of the polymer components increases, the PVP content at which crystallinity in PVA is no longer observed decreases. The wide band representing hydroxyl stretching splits into four components at welldefined frequencies which are assigned to (1) multiple hydroxyl‐hydroxyl bonding in organized PVA regions, (2) hydroxyls which are simply bonded to carboxyl, (3) hydroxyls doubly bonded to two carbonyls or to one carbonyl and one hydroxyl, and (4) simple hydrogen‐hydrogen bonding in amorphous PVA regions. When the PVP content increases, the relative intensity of the bond of di‐hydrogen‐bonded hydroxyls remains quasi‐invariant, while that of multiple hydrogen bonds in PVA decreases, and that of simple hydroxyl‐carbonyl bonds increases correspondingly. It appears that the higher the molecular weight, the more effective the hindrance of PVP crystallization. An explanation of the mechanism leading to the formation of different structures in the blends is proposed on the basis of these results. It stresses the importance of the role of chain dynamics in an entangled chain network, which greatly affects the kinetics of crystallization of PVA during the drying step.