Thermoresponsive hydrogels obtained by gamma radiation: Poly(alkylene glycol) methacrylates vs. poly(n-isopropylacrylamide)

This study offers a comparative analysis of two most important types of thermoresponsive hydrogels: poly(N-isopropylacrylamide) (PNiPAM) and poly(alkylene glycol) methacrylates (PAGMA). The latter includes poly(oligo(ethylene glycol) methacrylate) (POEGMA), a moderately hydrophilic polymer, and poly(oligo(propylene glycol) methacrylate) (POPGMA), its more hydrophobic counterpart. The hydrogels were produced using gamma irradiation in three different solvent systems: demineralized water, a water/ethanol mixture, and pure ethanol. Gel fraction measurements were used to assess the effects of monomer type, irradiation dose, and solvent composition on crosslinking efficiency. Swelling behavior was examined over a wide temperature range, highlighting distinct thermoresponsive features and volume phase transition temperatures (VPTTs). Differential scanning calorimetry (DSC) confirmed the presence of temperature-dependent phase transitions, while structural and chemical changes caused by radiation-induced crosslinking were analyzed using Fourier-transform infrared (FTIR) spectroscopy. Results showed that effective hydrogel formation is achievable at relatively low radiation doses. The choice of synthesis medium significantly influenced the formation and the gelation efficiency of hydrogels. Particularly, PNiPAM hydrogels were successfully synthesized without the use of alcohol and still demonstrated excellent swelling capacity and VPTTs near physiological temperatures, making them suitable for biomedical applications. These findings provide valuable insights for designing advanced smart hydrogels for biomedical and environmental uses.