LOWER CRITICAL SOLUTION TEMPERATURES OF POLYISOBUTYLENE PLUS ISOMERIC ALKANES

Lower critical solution temperatures (LCST) have been obtained for polyisobutylene and some thirty isomeric pentanes, hexanes, heptanes and octanes. The LCSTs found with cyclic alkanes are about 125 deg. C higher than those with the corresponding normal alkanes. Branched isomers of the same number of carbon atoms give LCSTs which vary over some 50 deg. C. These variations in LCST are explained in terms of the differing free volumes of the solvents as shown by their different thermal expansion coefficients, and which arise from their different 'structural factors' in the Prigogine theory of solutions. The theory, with the approximation of a van der Waals liquid as recently used by Flory and collaborators, is successful in correlating the LCSTs but not in giving a quantitative prediction of the values. © 1969.