Influence de la nature du solvant et de la température sur les dimensions non perturbées des copolymères statistiques PS–PMM

Abstract

Abstract The STOCKMAYER‐FIXMAN method has been applied to determine the unperturbed dimensions of a polymer chain from viscosity measurements on several fractions in a good solvent. Homopolymers yield values of the unperturbed dimensions which are independent of the nature of solvent and which hardly depend upon temperature. Using the same method for [η] measurements in different solvents, the values obtained for random copolymers PS–PMMA are quite different from the “ideal” values calculated on the basis of additivity rules from the unperturbed dimensions of corresponding homopolymers. The discrepancy was shown to depend on the χ AB parameter, which also governs the critical concentration for phase separation for a solution of the corresponding homo polymers. Since χ AB is solvent and temperature dependent, the observed variation in the unperturbed dimensions from one solvent to another can be qualitatively explained. Linear relation was found between χ AB and K Θ leading to K Θ “ideal” for χ AB = 0. Moreover, the temperature dependence of unperturbed dimensions for a random copolymer, in a given solvent, is much stronger than for an homopolymer. As temperature increases χ AB decreases and the unperturbed dimensions approach the “ideal” values. These results show the influence of heterocontact interactions on chain conformation. They clearly demonstrate their importance at theta conditions by influencing the dimensions of the chain.