Low-temperature degradation of poly(vinyl alcohol)-silica composite

The poly(vinyl alcohol) (PVA)--silica composite was prepared by hydrolyzing tetraethyl-orthosilicate in aqueous PVA solution. The dried xerogel obtained was heated at relatively low temperatures (60-100 deg C), and the resulting material was characterizaed by optical (ultraviolet, visible, and infrared) absorption and ESR spectroscopies. The PVA--silica composite and also PVA alone degraded at 60-100 deg C to form conjugated double-bonds in the carbon chain of PVA, accompanying the generation of some organic radicals through C--C bond cleavage. The amount of the radical increased monotonously in the initial stage and approached a constant value. In contrast, the PVA to which hydrochloric acid was added initiated the degradation early and did not show such a cessation of increase in the amount of the radical. The chemical bonding between PVA and silica appears to depress the cleavage of the C skeleton of PVA. Graphs, Spectra. 8 ref.--AA