This work deals with the modification reaction of poly(viny1 alcohol) with n-alkyl chloroformates using pyridine as catalyst. The structure of the modified polymers was determined by means of IR, 'H and l3C-NMR spectroscopy as well as by chemical analysis. Vinyl alcohol-vinyl n-alkyl carbonate copolymers were obtained. The presence of cyclic carbonates has not been observed. It has been found a linear dependence of reaction rate on polymer, n-alkyl chloroformates, and pyridine concentrations, respectively. The activation energy found was of 15.4 kcal/mol. The water absobrbed in the copolymers made it reasonable to conclude that the hydrophilic character of the copolymers decreased progressively when either the carbonate groups content or the side chain length increased. Water insoluble alcohol-vinyl n-alkyl carbonate copolymers were hydrolyzed in an alkaline medium. They were found to recover their solubility in water after a certain hydrolysis extent was reached. ZUSAMMENFASSUNG:Die Umsetzung von n-Alkyl-chlorformiat mit Polyvinylalkohol, katalysiert durch Pyridin, wurde untersucht. Die Struktur der modifiiierten Polymeren wurde durch IR-, 'H-und 13C-NMR-Spektroskopie und chemische Analysen bestimmt. Es entstehen Vinylalkohol-Vinyl-n-alkylcarbonat-Copolymere. Die Anwesenheit von cyclischen Carbonaten wurde nicht beobachtet. Es wurde eine lineare Abhangigkeit der Reaktionsgeschwindigkeit von den Konzentrationen an Polymerem, n-Alkyl-chloroformiat und Pyridin gefunden. Die Aktivierungsenergie ergab sich zu 15.4 kcal/mol. Das im Copolymeren absorbierte Wasser 1Mt den SchluB zu, da8 der hydrophile Charakter des Copolymeren allmahlich abnimmt, wenn der Gehalt an Seitenkettensubstanz steigt. Im Wasser unlosliche Vinyl-alkohol-Vinyl-n-alkylcarbonat-Copolymere wurden in alkalischem Medium hydrolysiert; nach einem bestimmten Hydrolysegrad gewinnen die Polymeren die Wasserl6slichkeit zuruck.
I3C NMR spectroscopy was used for the determination of the sequence distribution in vinyl alcohol-ethyl vinyl carbonate copolymers prepared by reaction of poly(viny1 alcohol) with ethyl chloroformate. The l3C NMR spectra of the methylene carbons in the main chain show three split peaks whose intensities change with copolymer composition. These peaks can be assigned to the three dyad sequences. The obtained results show that ethyl vinyl carbonate units have an alternating tendency in the copolymer chain. The Tg values of the vinyl alcohol-ethyl vinyl carbonate and vinyl alcohol-butyl vinyl carbonate copolymers are influenced by both the overall copolymer composition and the monomer sequence distribution.
A kinetic study of the hydrolysis of vinyl alcohol-vinyl n-alkyl carbonate copolymers has been made as a function of the base or acid concentration, the temperature, and the structure of the carbonate units. The homogeneous hydrolysis in alkaline medium was found to be first order with respect to both the hydroxyl ion and the carbonate; the acid hydrolysis was of first order with respect to the acid concentration. The heterogeneous hydrolysis in alkaline medium followed a pseudo-first-order kinetics with respect to the base concentration; the hydrolysis rate was affected by the carbonate content and the structure of the carbonate units. The activation energies obtained for the acid and base catalyzed homogeneous hydrolysis and the base catalyzed heterogeneous hydrolysis were 13.8, 10.0, and 10.3 kcal/mol, respectively. a-Chymotrypsin was inactive in the hydrolysis experiments carried out with these copolymers. ZUSAMMENFASSUNG:Es wurde die Kinetik der Verseifung von Vinylalkohol-Vinyl-n-alkylcarbonat Copolymeren in Abhangigkeit von der Saure-und Basen-Konzentration, der Temperatur und der Art der Carbonatgruppen untersucht. Die homogene basenkatalysierte Verseifung verlauft nach einer Reaktion erster Ordnung in bezug auf die Hydroxylund Carbonatgruppen-Konzentration, wahrend die saurekatalysierte Verseifung in Bezug auf die Saure-Konzentration eine Reaktion erster Ordnung ist . Die heterogene basenkatalysierte Verseifung hangt von der Konzentration und der Art der Carbonatgruppen ab. Fur die saure und basische homogene Verseifung wurden Aktivierungsenergien von 13.8 und 10.0 kcal/mol erhalten. Fur die heterogene basenkatalysierte Verseifung ist eine Aktivierungsenergie von 10.3 kcal/mol erhalten worden. a-Chymotrypsin zeigte sich als unwirksam bei den hier durchgefuhrten Verseifungsreaktionen.
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