Thermo-Induced Double Phase Transition Behavior of Physically Cross-Linked Hydrogels Based on Oligo(ethylene glycol) methacrylates

Double thermosensitive clay/P(MEO(2)MA-co-POEGMA) nanocomposite (NC) hydrogels are prepared by in situ free radical polymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO(2)MA) and oligo(ethylene glycol) methacrylate (OEGMA) in the presence of physical cross-linker clay. The temperature-induced phase transition behavior of NC hydrogels is investigated by turbidity, temperature dependent nuclear magnetic resonance, and variable temperature Fourier transform infrared spectroscopy. 2D infrared analysis is employed to study the sequential order of changes of all groups in NC hydrogels during the heating and cooling process. The obtained novel clay/P(MEO(2)MA-co-POEGMA) NC hydrogels exhibit an unusual thermally induced multistep aggregation process and successively undergo three consecutive microstructural changes: loose clay/polymer microaggregation homogeneous network structure dense clay/polymer macroaggregation. Dynamic light scattering and transmission electron microscopy measurements show similar results of the NC nanogel at the same temperature regions, confirming the three consecutive microstructural changes. This new generation of thermosensitive hydrogel offers promising potential for applications as smart devices, biomedical materials, and drug carriers.