Structure of Poly(vinyl Alcohol) Films Iodinated in Solution before Casting

Unoriented iodinated films (IBC films) were prepared by casting aqueous solutions of 10 wt% poly(vinyl alcohol)(PVA) containing selected quantities of I$_2$/KI. The quantity of I$_2$/KI was controlled to obtain 15.2, 79.8, 83.2, 117.0, and 140.1% weight gains. The structure of the films before and after deiodination was investigated by thermogravimetry(TG), X-ray differaction analysis, differential scanning calorimetry(DSC), and dynamic mechanical thermal analyser(DMTA). The TG curves of IBC films exhibited three distinct zones of weight loss corresponding to the evaporation of $H_2O$ and I$_2$ molecules (zone I), evaporation of I$_2$ and partial decomposition of side groups(-OH)(zone II), degradation of the remaining side groups and partial degradation of main chain(zone III-1 ), and desradation of the remaining main chain and char zone corresponding to KI, which is similar to films iodinated after casting(IAC films). But the weight loss of zone I is lower and the percent of char is higher than those of the IAC film. The crystalline structure of film with weight gain of 15.2% was silmilar to that of a pure PVA, structure of films of weight gain of 77.8~117.% gradually became similar to that of IAC film with increasing weight gain, but the film with weight gain of 140.1% was almost amorphous. The DSC thermograms of IBC films with weight gains of 15.2 and 39.8% indicated endothermic single or double peaks at around 180 $^{\circ}C$ correlponding to the crystal melting and degradation of side groups, those with weight gains of 83.2% and over indicated exothermic peak at around 17$0^{\circ}C$ which may be corresponding to crystallization, and broad endothermic peak at around 180~20$0^{\circ}C$ corresponding to the crystal melting and degradation of side groups. The dynamic mechanical un transition of the IBC film with weight gains of 140.1% appeared around 2$0^{\circ}C$. X-ray diffraction and DSC analysis of deiodinated films showed that the crystal struoture on deiodination of all IBC films, regardless of crystallinity, returned to that of the pure PVA films.

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