Characterisation of water sorption in gamma irradiation of bulk-copolymerized hydroxyethylmethacrylate hydrogels

Hydrogels have many applications in ranging from biomedicine to engineering areas. Since the discovery year of hxdrogel, the properties of hydrogels have been developed and improved to suit the recent applications. Nevertheless. in pure chemistry. we are interested in characterising the water uptake and sorption behaviours of purified polyhydroxyethylmethacrylate (pHEMA) and its crosslinked copolymers with mono-, di-, tri- and tetra-ethyleneglycoldimethacrylate. These polymers were prepared by mean of gamma irradiation to a specified dose. Therefore advantage is also taken to observe the water uptake of post-polymerized pHEMA. The advantage of the irradiation method is that no potentially toxic initiator fragments or catalyst residues remain in the polymeric matrix. Irradiation can also be used to introduce crosslinks into the polymer. The aim of this paper is to investigate the bulk copolymerization of hydroxyethylmethacrylate (HEMA) and crosslinkers to high conversion by mean of gamma irradiation at ambient temperature and different doses. The diffusion study was performed based on the amount of water diffused into the polymer for a period of approximately one month. The equilibrium water contents of increasing percentage of crosslinked polymers were observed to be relatively similar. With the exception, the greatest percentage (0.5%) would swell to lesser degree compared to the least one (0.2%). The plotting at square root time suggests that the diffusion follows the Case I Fickian behaviour. This behaviour leads to the calculation of diffusion coefficients according to equation: Mt/M∞ = 4/π1/2(Dt/a2)1/2 - Dt/a2- ....The obtained coefficients would enable further computerised simulations of the diffusion and graphic drawings can be simulated to represent the overall diffusion of each copolymer