Heterogeneous surface saponification of suspension-polymerized monodisperse poly(vinyl acetate) microspheres using various ions

Abstract

Poly(vinyl alcohol) (PVA)/poly(vinyl acetate) (PVAc) microspheres with a skin/core structure were prepared through the heterogeneous surface saponification of PVAc microspheres suspension-polymerized. The PVA skin formed through the heterogeneous saponification was hydrogel swellable in water. In addition, to obtain morlodisperse PVA/PVAc microspheres having various skin/core ratios and morphologies, the ion-specificities to the heterogeneous saponification were investigated using SO42-, Cl-, NO3-, Br-, and I- for anions and Li+, Na+, and K+ for cations, respectively. The ions were not specific significantly to the rate of the heterogeneous saponification, while were related to the degree of saponification (DS). DSs had different values between by weight loss (DSw) and by proton nuclear magnetic resonance spectroscopy (DSNMR) measurements. The order of DS(w)s was SO42- < Cl- < NO3- < Br- < I- for anions and K+ < Na+ < Li+ for cations, and that of DSNMRS, I- < Br- < NO3- < Cl- < SO42- for anions and Li+ < Na+ < K+ for cations. The differences in values between DSws and DSNMRS were caused by the dissolution of PVA skin and significantly decreased for SO42-. The peaks at melting temperature of PVA were sharp and their areas were large for ions deswelling PVA skins. (c) 2006 Wiley Periodicals, Inc.