Solubility characteristics of poly(ethylene oxide): Effect of molecular weight, end groups and temperature

Abstract

The general solvation equation

$${\text{Log }}L = c + r \cdot R_2 + s \cdot \pi _2^{\text{H}} + a \cdot \alpha _2^{\text{H}} + b \cdot \beta _2^{\text{H}} + l \cdot \log {\text{ }}L^{16} $$

has been used to evaluate the effect of molecular weight, hydroxyl end groups and temperature on the solubility characteristics of poly(ethylene oxide), PEO. In this equationL is the gas-liquid partition coefficient of a series of probes on PEO, and the explanatory variables are solute properties describing the excess molar refraction,R ₂, the probe dipolarity-polarisability, π ^H₂ , and the probe hydrogen-bond acidity and basicity, α ^H₂ and β ^H₂ .L ¹⁶ is the gas-liquid partition coefficient of the probe onn hexadecane at 298 K. Ther·R ₂ andl·logL ¹⁶ terms increased with increase in molecular weight whereas thes·π ^H₂ and a α ^H₂ terms decreased; in all cases theb·α ^H₂ term was not significant. Since thes-constant is a measure of polymer polarity-polarisability, and thea-constant a measure of polymer basicity, we deduce that these polymer properties decrease with increasing molecular weight. Chains with molecular weight below 3000 showed a more rapid decrease in basicity compared to the higher molecular weight species. Thes·π ^H₂ ,a·α ^H₂ andl·logL ¹⁶ terms all decreased with increase in temperature. Finally, the contribution of the terminal hydroxyl groups to the total polymer basicity was evaluated and discussed.