High molecular weight syndiotacticity-rich poly(vinyl alcohol) gel in aging process

The properties of the aged gels of high molecular weight syndiotacticity-ri ch poly(vinyl alcohol)s (HMW S-PVAs) with different syndiotactic diad (s-di ad) contents were investigated. HMW S-PVA gels with s-diad content of 61.5% and 58.2% showed the rapid increases of the syneresis and the turbidity fr om the early stage of aging time, which is ascribable to the phase separati on, while that with s-diad content of 55.7% did not. From the morphological study, it was confirmed that the phase separation in HMW S-PVA gel with s- diad content of 61.5% occurred without the liquid-liquid phase separation i n sol state, whereas both the liquid-liquid phase separation in sol state a nd the subsequent phase separation in gel state occurred in the case of HMW S-PVA gel with s-diad content of 58.2%. On the other hand, HMW S-PVA gel w ith s-diad content of 55.7% showed neither the liquid-liquid phase separati on in sol state nor the phase separation in gel state in the long period of time. Tt was also confirmed from wide angle X-ray diffractogram that the c rystallization was accompanied by the phase separation in gel state in the aging process of PVA gel. However, the crystallization was hindered by the fast network formation at the initial stage of time. Later the syndiotactic ity promoted the crystallization. The tensile modulus of HMW S-PVA gel with higher syndiotacticity increased more significantly with time.