THE EFFECTS OF SPECIFIC INTERACTIONS ON THE SURFACE-STRUCTURE AND COMPOSITION OF MISCIBLE BLENDS OF POLY(VINYL ALCOHOL) AND POLY(N-VINYL-2-PYRROLIDONE)

Poly(vinyl alcohol) (PVAL)/poly(N-vinyl-2-pyrrolidone) (PVP) blends we re studied by differential scanning calorimetry (d.s.c.), Fourier tran sform infrared spectroscopy (FTi.r.), and X-ray photoelectron spectros copy (XPS). A single glass transition temperature (T-g) was observed f or all PVAL/PVP blends, suggesting that PVAL/PVP blends are miscible w ithin the compositions considered. The specific interaction (hydrogen bonding) between PVAL and PVP was investigated by d.s.c. and FTi.r. Th e surface chemical composition of the blends was studied by XPS. The X PS result showed that PVAL is enriched on the surface of the PVAL/PVP blends in spite of the formation of intermolecular hydrogen bonds betw een the C=O in PVP and the OH in PVAL. The intermolecular hydrogen bon ds also induce a change of 0.3-0.4 eV in the Ols binding energy differ ence between the oxygen atoms in the carbonyl and hydroxyl groups. It can be concluded that the formation of the intermolecular hydrogen bon ds is a major factor for the miscibility of the PVAL/PVP blends in the bulk and that the difference in the surface energy between PVAL and P VP is the dominant factor that controls the surface composition of the blends. (C) 1998 Elsevier Science Ltd. All rights reserved.