INFLUENCE OF SYNDIOTACTICITY ON POLY(VINYL ALCOHOL)-IODINE COMPLEX-FORMATION

The extent of colour development in an aqueous poly(vinyl alcohol) (PV A)-iodine complex solution increased with increasing syndiotacticity u p to a certain syndiotactic content, then decreased with increasing sy ndiotacticity. The complex formation depended on the content of the sy ndiotactic pentad sequence length in the PVA molecules. The most suita ble content of the syndiotactic pentad for forming complexes was aroun d 12% in the case of reaction at 30 degrees C. A 0.5% solution of synd iotactic PVA (S-PVA) with an syndiotactic diad (s-(diad)) content of 6 3.8% 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) con tent of 63.8% was hardly coloured. In the solutions containing two kin ds of s-PVA having different syndiotacticities, additivity for the ext ent 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 colou r development at higher syndiotacticity was due to the formation of mi crogels. The absorption maximum shifted to a longer wavelength with in creasing syndiotacticity. The length of polyiodine increased with incr easing syndiotacticity.