Mixing enthalpy and liquid–liquid equilibrium of aqueous polyethylene glycol (PEG) solutions

Abstract

Polyethylene glycol (PEG) is one of the most important polymers in pharmaceutical or medical applications at room or at body temperature, where polymers with different chain lengths are employed. The purpose of this work is the analysis of a detailed association model taking into account self-association of water, self-association of polymer and cross-association. The model is applied in two different versions (model 1 without end-group effects and model 2 with end-group effects) to the correlation and prediction of liquid–liquid equilibria (LLEs), mixing enthalpies and hydration numbers of PEG in an aqueous solution. The required model parameters are estimated by fitting selected LLE data at high temperatures and some data points for the mixing enthalpy at low temperatures. The optimised set of parameters is used to predict simultaneously the effect of the polymer molecular weight on miscibility, the mixing enthalpy as a function of chain length and temperature as well as the number of hydration as a function of molecular weight and temperature. The obtained results were in fair agreement with experimental data from the literature. Additionally, some new mixing enthalpies were measured using isothermal titration calorimetry.