Multimethacryloxy-POSS as a crosslinker for hydrogel materials

Hybrid hydrogel materials derived from two types of polymethacrylates: rigid and flexible, crosslinked with methacryloxy-multifunctionalized polyhedral oligomeric silsesquioxane (M-POSS) were obtained in a photo-induced copolymerization process. The base monomers were 2-hydroxyethyl methacrylate (HEMA; forming a rigid polymer) and a mixture of oxyethylene glycol (di)methacrylates (forming an elastomer). Investigations included the kinetics of hybrid materials formation and selected physical and mechanical properties. The obtained results were discussed in terms of effects of H-bonding and viscosity of compositions before curing, additional crosslinking, the presence of POSS cage, M-POSS aggregation and rigidity/flexibility of the base polymer. It was found that physical factors (diffusion, tendency to aggregation) dominate over interactions between reacting molecules (H-bonding) during the formation of the hybrid polymer structure. Disorder in H-bonding in HEMA-based material is responsible for the appearance of the antiplasticization effect manifesting itself by the lowering of the Tg value with simultaneous increase in the Young modulus. Antiplasticization behavior affects also thermal stability of the HEMA-based materials. In general, cross-linking of the rigid and elastomeric material with M-POSS gives quite different results; moreover, the HEMA-based materials show an exceptional behavior. The results presented are important indications in the selection of technological curing parameters in preparation of M-POSS-containing hydrogel materials.