Influence of monomer and crosslinker molar ratio on the swelling behaviour of thermosensitive hydrogels

The synthesis of the poly(N-isopropylacrylamide-co-2-hydroxypropylmethacrylate) hydrogel along with the analysis of the residual monomers content and influence of monomer and crosslinker molar ratios on the swelling behaviour was investigated. Synthesis of thermosensitive hydrogel based on N-isopropylacrylamide was carried out with the molar ratios of 5, 10, 15 and 20 mol. % of monomer 2- hydroxypropyl-methacrylate, in the presence of ethylene glycol dimethacrylate as a crosslinker (1, 1.5, 2 and 3 mol. %) and 2,2'-azobis(2-methylpropionitril) as an initiator in acetone. The quantities of residual monomers in the synthesized copolymers were determined by HPLC method, ranging from 0.19 to 0.49 % for N-isopropylacrylamide and from 0.13 to 0.63 % for 2-hydroxypropyl-methacrylate, counting the amount of xerogel. The hydrogels swelling ratio depending on time at 20 and 40°C was examined. It was found that hydrogel with 5 mol. % 2-hydroxypropyl-methacrylate and 1 mol. % ethylene glycol dimethacrylate had the highest degree of swelling (α = 29.59) at 20°C, and that hydrogel with 20 mol. % 2-hydroxypropyl-methacrylate and 3 mol. % ethylene glycol dimethacrylate had the lowest swelling degree (α = 2.17) at 40°C