Role of degree of saponification in the shear-induced molecular orientation of syndiotacticity-rich ultrahigh molecular weight poly(vinyl alcohol)

Rheological and morphological properties as well as crystal characteristics of syndiotacticity-rich ultrahigh molecular weight poly(vinyl alcohol) (PV A) were studied with consideration of degree of saponification (DS). The so lutions of syndiotacticity-rich PVA with DS higher than 90% in dimethyl sul foxide exhibited shear-thinning behavior without lower Newtonian flow regio n, implying the presence of heterogeneity. From the logarithmic plot of G ' vs G ", the modified Casson plot, and the variation of relaxation time wit h DS, the syndiotacticity-rich PVA chains with high DS were elucidated to h ave a nature of molecular alignment under shearing deformation through the formation of microgels. These characteristic theological features have a st rong relationship with the development of the microfibrillar structure in t he course of saponification of poly(vinyl pivalate). The well-oriented micr ofibrillar structure was observed in the syndiotacticity-rich PVA with high DS, which resulted from the hydrogen-bonding generation during saponificat ion.