Water sorption of flexible networks based on 2- hydroxyethyl methacrylate-triethylenglycol dimethacrylate copolymers

Abstract

Cross-linked films of copolymer of 2-hydroxyethylmethacrylate (HEMA) and triethylenglycoldimethacrylate (TEGDMA) were prepared by free radical polymerization initiated at 60°C. The swelling behaviour of films prepared with 2, 5 and 10 mol% of TEGDMA was followed gravimetrically and the diffusion coefficients were determined according to the Fickian law at several temperatures in the interval 25–50°C. The apparent activation energy was independent of the composition of the networks, giving a value of 15.5 kJ mol−1 which corresponds to a typical diffusion process. The freezing point, the enthalpy of fusion and the amount of non-freezable water were determined by differential scanning calorimetry (DSC) on hydrated samples with different hydration degree. There is a critical hydration interval (W = 20–30 wt%) in which it is possible to distinguish the different states of water in the cross-linked hydrogel. The variation of the enthalpy ΔHf with the hydration degree gives a maximum amount of non-freezable water of about 23 wt%, independent of the TEGDMA content of copolymer systems