FORMATION OF POLY(VINYL ALCOHOL) IODINE COMPLEXES IN SOLUTION

The effect of the dissolved state of poly(vinyl alcohol) (PVA) molecul es in water on the color development due to PVA-iodine complexes was i nvestigated at each given PVA and iodine concentration using two kinds of syndiotactic-rich PVA (S-WA) which are unstable in water because o f the formation of intermolecular hydrogen bonds and form the complex easily. In the reaction mixtures prepared by mixing PVA solutions and an iodine solution, the color development was constant and independent of standing time of the PVA solution before the addition of iodine up to a certain time, after which it decreased with the standing time. T he color development obtained with use of the PVA solution allowed to stand for a fixed time was higher for S-PVA with a lower s-(diad)%. In the case of the reaction mixture prepared by dissolving PVA in an iod ine solution, the color development was higher for S-PVA with a higher s-(diad)%. The initial ratio of the I-5-I-/(3)- and the rate of decre ase in the ratio of I-5(-)/I-3(-) were larger than those in the preced ing case. The color development decreased for the PVA with an s-(diad) % of 58, whereas it increased for the PVA with an s-(diad)% of 61.3 wi th increasing propanol content, an inhibitor of gelation. From these r esults, the aggregates of PVA molecules have been assumed to play an i mportant role in forming the complexes. (C) 1997 John Wiley & Sons, In c.