Upper and lower critical solution temperatures in 1-octanol solutions of polyethylene

Abstract

Cloud points of 1-octanol solutions of four linear polyethylene samples having different molecular weights were measured visually in both regions of the upper and lower critical solution temperatures (UCST and LCST). From the (temperature, polymer weight fraction) phase diagrams drawn, the UCST and LCST were determined. These data were plotted according to Shultz and Flory, to yield the results of ΘU = 444 K and ψ1,U = 1.16 for the UCSTS and ΘL = 621 K and ψ1,L = −5.4 for the LCSTs. Here, Θ is the Flory theta temperature, ψ1 is the entropy of dilution parameter, and the subscripts U and L refer to the UCST and LCST respectively. The interaction parameter χ1 of the present solutions over the temperature range from ΘU to ΘL was first estimated according to the Eichinger version of the classical lattice theory. Secondly, the Flory and the Patterson polymer solution theories were applied in order to obtain the information on each contribution of cohesive energy and free volume to χ1(T) separately. It was found that the final results significantly depend upon the reference temperature at which the equation-of-state parameters are determined. This finding suggests that the temperature reduction in the Foory theory is inadequate.