Some thermodynamic properties of slightly cross‐linked styrene‐divinylbenzene gels

Abstract

Abstract A study has been made of the swelling characteristics of Styrene‐divinylbenzene gels containing from 0.02 to 0.12% of the cross‐linking agent. Variation in swelling of samples containing the same amount of divinylbenzene was shown to increase with decreasing divinylbenzene concentration. The influence of amount of cross‐linking agent, type of solvent, and temperature, on equilibrium swelling is reported. By assuming that μ g is 0.44 for polymer‐toluene, values of μ g for over 50 different solvents have been obtained. No values of μ g below 0.42 were found. A correlation of swelling values and of μ g values with cohesive energy densities of the solvents is presented. The polymer appears to have a cohesive energy density of 82 cal. per cc. Equilibrium swelling decreases slightly in toluene and methyl ethyl ketone but increases markedly in cyclohexane with rising temperature. Efforts to calculate gel constants from the temperature coefficient of swelling failed completely in the case of cyclohexane, and were only moderately successful with toluene. These temperature studies, and the cohesive energy density correlations both appear to indicate a lack of complete understanding about the physical significance of μ, and why it depends so markedly on concentration.