Investigations of poly(vinyl alcohol)/poly(N‐vinyl‐2‐pyrrolidone) blends, 1. Compatibility

Abstract

Abstract Blends of crystallizable poly(vinyl alcohol) (PVA) with poly( N ‐vinyl‐2‐pyrrolidone) (PVP) made from aqueous solutions appear to be miscible in the whole composition range according to DSC results. A large negative value of the interaction parameter between the two polymers was found from melting point depressions. IR spectroscopy evidenced compatibility of the two polymers on a molecular level. DSC, density and IR results all show a proportion of pure PVA crystallites in blends, which decreases with increasing PVP content and becomes nil at about 50 wt.‐% of PVP. However, close examination of the hydroxyl stretching region of the blends indicates the presence of organized regions of PVA beyond this limit. According to IR results, the sequence of decreasing hydrogen‐bonding power should be the following: multiple hydroxyl‐hydroxyl bonding in organized PVA regions, hydroxyl‐carbonyl bonding between the two polymers, and simple hydrogen‐hydrogen bonding in amorphous PVA regions. It appears that the PVA component can be held in the amorphous state by hydrogen bonding with the PVP component when there is a sufficient amount of the latter in the blend. The amorphous part of PVA is compatible with PVP, but the crystallizable part is not in its most stable form.