Effect of syndiotactivity on the aqueous poly (vinyl alcohol) gel
The mechanism of gelation of aqueous solution of syndiotacticity-rich poly(vinyl alcohol) (PVA) and the structure of junctions in gel were studied. Melting points (T m ) of the gels were measured according to Ferry’s procedure. Gelling ability was highly promoted by slight increase in syndiotactivity. The relation between the concentration of PVA and T m was not linear in the region of lower concentration of PVA. Three types of intermolecular hydrogen bond were assumed following the concentration of PVA. The gels chilled at lower temperature of PVA having the content of syndiotactic diads above 60.9% showed remarkable syneresis accompanying the rise of temperature. This phenomena seems to be a result of the breakdown of the unstable junctions and further growth of the crystallites. The X-ray diffraction pattern of the gel chilled at higher temperature was clearer than that at lower temperature and that pattern because progressively clearer with increasing content of syndiotacticity. These results lead to the conclusion that the structure of junction in network of PVA-water gel must consist of crystallites formed by the syndiotactic sequence parts.
KeywordsVinyl Alcohol Vinyl Acetate Aqueous Poly Syndiotactic Sequence Apparent Melting Point
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