EtudePARspectroscopie de la deshydratation de dérivés de l'alcool polyvinylique: Mise en evidence d'une répartition séquentielle des substituants

摘要

AbstractThe dehydration of sulfopropylic and alkyl derivatives of poly(vinyl alcohol), with varying degrees of substitution, was observed using ultraviolet and visible spectroscopy. The dehydration reactions were carried out in a KHSO4/heptane system kept under nitrogen at 100°C. Spectroscopic results show that definite sequences of conjugated double bonds are formed. The distribution of the number and length of these conjugated sequences was determined and compared with the theoretical values obtained assuming statistical distribution of the substituents. From this work it is concluded that: (1) the grafting of propane‐sultone onto poly(vinylalcohol) molecules does not follow a random, statistical pattern, rather the reaction is sequential, i.e., of a “zip” type. The product molecules contain blocks of sulfopropylic‐substituted vinyl alcohol groups. (2) The grafting of alkyl groups onto the poly(vinyl alcohol) molecules also occurs in a sequential manner. Results obtained show that the polymer chains contain at least two unreacted hydroxyl functions between each substituent alkyl group; this is in agreement with x‐ray studies of these derivates. Further evidence of an ordered distribution of the substituents along the polymer chain is given by the heterogeneity in the compositions of the substituted polymers. The difference in the observed structures of the two substituted polymers demonstrates the importance of the nature of the substituents in determining the reaction mechanism. It is concluded that the structural differences observed are due to differences in the solubility of the sulfopropylic and alkyl reactants in the original reaction medium, and the hydrophilic and hydrophobic character of the sulfopropylic and alkyl substituents in t