Flory Enthalpy Parameter at Infinite Dilution of Polymer Solutions Determined by Various Methods

Abstract

The Flory enthalpy parameter at infinite dilution κ0 was evaluated for atactic polystyrene (PS)–cyclohexane (CH) and –trans-decalin (D) systems by applying the following four methods from literature data: (1) Temperature dependence of vapor pressure and membrane osmotic pressure, (2) critical solution temperature Tc and critical solution concentration vpc for a series of solutions of polymers, (3) temperature dependence of the second virial coefficient in the vicinity of the Flory theta temperature θ, and (4) calorimetry. In method 2, Shultz–Flory, Stockmayer, Koningsveld et al. (KKS), and Kamide–Matsuda (KM)’s procedures were applied to estimate θ and the entropy parameter ψ0, from which κ0 was calculated as ψ0θ/T(T, temperature). κ0 values at θ deduced by these methods (in method (2), by KKS and KM treatments) yielded a single master curve against the weight- or number-average molecular weight M̅w or M̅n; κ0 (at θ) =0.924M̅w-0.089 for PS–CH system. Excellent agreement (±0.02) was confirmed between κ0 values at θ deduced by various methods when M̅w (or M̅n) of the polymer was the same. This fact strongly supports the validity of the modified Flory–Huggins solution theory, in which the polymer–solvent interaction parameter χ depends on the polymer concentration and its molecular weight.