Temperature dependence of unperturbed dimensions for isotactic poly(2‐hydroxyethyl methacrylate)

Abstract

AbstractThe unperturbed dimensions of isotactic poly(2‐hydroxyethyl methacrylate) (PHEMA) were evaluated from intrinsic viscosity measurements in water, ethanol, 1‐propanol, 2‐propanol, and 2‐butanol under θ conditions over the temperature range of 3.7–32.1°C. The smallest value of unperturbed dimensions (Kθ) and the largest negative temperature dependence of unperturbed dimensions and the polymer–solvent interaction parameter (B) were obtained in aqueous θ solvent relative to the corresponding organic θ solvents. These results were interpreted by the hydrophobic interaction between the hydrophobic groups of isotactic PHEMA and water solvent. The temperature coefficient of the unperturbed dimensions, d ln〈r〉/dT, obtained in this study has a negative value of −1.44 × 10−3 deg−1 under chemically similar θ solvents such as ethanol, 1‐propanol, 2‐propanol, and 2‐butanol where specific solvent effects are eliminated or minimized. In order to obtain the thermodynamic parameters for mixing between isotactic PHEMA and solvents, the plots of the polymer–solvent interaction parameter versus reciprocal absolute temperature (1/T) were carried out. Both the entropy of dilution and enthalpy of dilution show the negative values for water, methanol, and t‐butanol, whereas the positive ones for ethanol, 1‐propanol, 2‐propanol, and 2‐butanol. This result indicates that the solution of isotactic PHEMA behave as exothermal systems in the former class of solvents and endothermal ones in the latter class of solvents.