Influence of Syndiotacticity on Poly(vinyl alcohol)-Iodine Complex Formation

The extent of colour development in an aqueous poly(vinyl alcohol) (PVA)-iodine complex solution increased with increasing syndiotacticity up to a certain syndiotactic content, then decreased with increasing syndiotacticity. The complex formation depended on the content of the syndiotactic pentad sequence length in the PVA molecules. The most suitable content of the syndiotactic pentad for forming complexes was around 12% in the case of reaction at 30 degrees C. A 0.5% solution of syndiotactic PVA (S-PVA) with an syndiotactic diad (s-(diad)) content of 63.8% changed into a sol, whereas that with an s-(diad) content of 58% did not change after standing for 2 h at 30 degrees C, and the colour due to the iodine complex in the latter was deeper than in the former. The gel prepared from the 0.5% solution of S-PVA with an s-(diad) content of 63.8% was hardly coloured. In the solutions containing two kinds of s-PVA having different syndiotacticities, additivity for the extent of colour development did not hold, and the extent was lower than the sum of that of the components. The decrease in the extent of colour development at higher syndiotacticity was due to the formation of microgels. The absorption maximum shifted to a longer wavelength with increasing syndiotacticity. The length of polyiodine increased with increasing syndiotacticity.