Estimation of miscibility and interaction for cellulose acetate and butyrate blends with N-vinylpyrrolidone copolymers

The miscibility of CA/P(VP-co-MMA) blends was examined as a function of DS of CA and the VP fraction in the copolymer composition, in an extension of the previous studies on cellulose ester blends using P(VP-co-VAc) as a counter component. It was observed by DSC thermal analysis that when CA of DS <= 2.5 and P(VP-co-AhMA) of VP > 30 mol-% were two blending components, most of the binary polymer systems were miscible, whereas the other combinations of DS and VP values led to an immiscible series of blends, a possible exception being the miscible pair of DS = 2.70 and VP = 100 mol-%. Results of FT-IR and solid-state C-13 Cp/AAAS NMR spectra measurements suggested the miscibility to be driven by the hydrogen-bonding interaction between the residual hydroxyls of CA and the carbonyls of VP units in P(W-co-MAAA), as in the case of CA/P(VP-co-VAc) blends where the range of miscible pairing of acetyl DS and VP fraction was rather wide. From evaluations of proton spin-lattice relaxation times in the NMR study, it was confirmed that the homogeneity of the miscible blends of CA/P(VP-co-MMA) was substantially on a scale within a few nanometers. To interpret the difference in the DS- and copolymer composition-dependence of the miscibility behavior between three blend systems, CA/ P(VP-co-MMA), CA/P(VP-co-VAc), and CB/P(VP-co-VAc), Krigbaum-Wall intermolecular interaction parameters were estimated by solution viscometry for different polymer pairs pertinent to those blends. In particular, discussion took into consideration the effectiveness of an intramolecular repulsive action between the two units (VP and VAc, or VP and AAMA) constituting the vinyl copolymers.