Molecular dimension and interaction parameters of polyacrylamide in water–dimethylsulphoxide mixtures: effect of temperature

The intrinsic viscosities [η] of polyacrylamides having different molecular sizes are measured at 30–50°C temperature in various mixtures of water (good solvent) and dimethylsulphoxide (DMSO, poor solvent). The observed result and the Huggins constant values show a significant variation of cosolvency as a function of solvent composition (ϕ) and temperature. The nature of plots of [η] vs. ϕDMSO indicates relative importance of entropy factors over energetic factors in determining molecular configuration at high temperature. The unperturbed dimensions (Kθ) of the polymer are determined by various methods, which agree well with each other and exhibit a minimum at ϕ=0.5. The temperature coefficients of the unperturbed dimension (K′) gives both positive and negative values depending on the solvent composition, which indicates the variation of compactness and the presence of low and high energy configurations as a function of solvent composition. Molecular extension factor (αn) and the chain rigidity (σ) values are evaluated and the influence of temperature is discussed.