Synthesis and characterisation of novel poly(N-vinylcaprolactam) hydrogels, cross-linked with N-hydroxyethyl acrylamide (HEA)

Poly(N-vinylcaprolactam) (PNVCL) was copolymerised using N-hydroxyethyl acrylamide (HEA) to synthesise thermosensitive chemically cross-linked hydrogels. Hydrogels were formulated and prepared using PNVCL as the thermosensitive component together with HEA as a chemical crosslinker. UV photopolymerisation was used as a method to decrease both polymerisation times and energy costs. Rheological and gel fraction properties were analysed to find the viscosity and networking of the samples. It was shown that the concentration of the HEA directly affects the hydrogels. Samples containing HEA 20% and greater, improved hydrogel shape and mechanical strength for a longer period when compared to samples containing lower HEA concentrations. This was also confirmed by the overall complex viscoelasticity, indicating a greater occurrence of covalent bonds within the network and structure of HEA hydrogels with increasing concentrations of HEA. Results positively provided for possible use in thermosensitive applications, such as sensors and on-off triggers rather than electrical triggers used in energy saving applications such as smart windows [1].