Lower critical solution temperature control and swelling behaviour of physically crosslinked thermosensitive copolymers based on N-isopropylacrylamide

In this contribution we have developed thermosensitive polymer matrices based on N-isopropylacrylamide (NIPAAm). Preparation of the hydrogels involved photopolymerisation of a combination of NIPAAm, 1-vinyl-2-pyrrolidinone (NVP) and distilled water, in appropriate amounts and contained a UV-light sensitive initiator called 1-hydroxycyclohexylphenylketone. As NIPAAm monomer could be readily dissolved in mixtures of liquid NVP and distilled water, the use of organic solvents was not required in the polymerisation process. Furthermore, chemical crosslinking agents are not needed in the synthesis. By alternating the feed ratio, hydrogels were synthesised to have lower critical solution temperatures (LCST) in the vicinity of 37 °C. This ability to shift the phase transition temperature of the gels provides excellent flexibility in tailoring transitions for specific uses. The transition temperature of the pseudo gels was established using cloud point measurement and modulated differential scanning calorimetry (MDSC). The chemical structure of the xerogels was characterised by means of Fourier transform infrared spectroscopy (Ftir), while swelling experiments in distilled water indicate that the swelling and dissolution behaviour of the gels is strongly temperature dependent.