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

Abstract

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. ϕ DMSO indicates relative importance of entropy factors over energetic factors in determining molecular configuration at high temperature. The unperturbed dimensions ( K θ ) 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 ( α n) and the chain rigidity ( σ) values are evaluated and the influence of temperature is discussed.