SOLUBILITY CHARACTERISTICS OF POLY(ETHYLENE OXIDE) - EFFECT OF MOLECULAR-WEIGHT, END-GROUPS AND TEMPERATURE

The general solvation equation Log L = c + r.R2 + s.pi2H + a.alpha2H b.beta2H + l.log L16 has been used to evaluate the effect of molecula r weight, hydroxyl end groups and temperature on the solubility charac teristics of poly(ethylene oxide), PEO. In this equation L is the gas- liquid partition coefficient of a series of probes on PEO, and the exp lanatory variables are solute properties describing the excess molar r efraction, R2, the probe dipolarity-polarisability, pi2H, and the prob e hydrogen-bond acidity and basicity, alpha2H and beta2H. L16 is the g as-liquid partition coefficient of the probe on n hexadecane at 298 K. The r.R2 and l.logL16 terms increased with increase in molecular weig ht whereas the s.pi2H and a alpha2H terms decreased; in all cases the b.beta2H term was not significant. Since the s-constant is a measure o f polymer polarity-polarisability, and the a-constant a measure of pol ymer basicity, we deduce that these polymer properties decrease with i ncreasing molecular weight. Chains with molecular weight below 3000 sh owed a more rapid decrease in basicity compared to the higher molecula r weight species. The s.pi2H, a.alpha2H and l.logL16 terms all decreas ed with increase in temperature. Finally, the contribution of the term inal hydroxyl groups to the total polymer basicity was evaluated and d iscussed.