Polyvinyl alcohol-polyethylenglycol blends. with tungstophosphoric acid addition: Synthesis and characterization

摘要

New materials, based on a Keggin-structured compound (tungstophosphoric acid) immobilized in a polymeric matrix formed by a blend of polyvinyl alcohol and polyethylenglycol with 400, 2000, and 6000 Da molecular weight, were prepared and characterized. Hydrogels with physical type links were produced, using the freezing-thawing technique, and are an alternative to the matrices traditionally obtained by developing chemical links by the use of cross-linkers. The supported tungstophosphoric acid retained its Keggin primary structure intact. There is evidence of a heteropolyacid-polymeric matrix interaction, which could occur between the PW12O40(3-) Keggin anions and protonated hydroxyl groups C-OH2+ of the support. An effective immobilization was achieved, because there was no anion solubilization when the materials were put in contact with toluene at reflux. By differential scanning calorimetry and thermogravimetrical analysis, it was observed that the materials containing tungstophosphoric acid can be used as catalysts in reactions carried out at temperatures lower than 160-200 degrees C, without degradation of the solids, the temperature being dependent on the tungstophosphoric acid content and, at a lesser extent, on the polyethylenglycol molecular weight. (C) 2007 Elsevier B.V. All rights reserved.