Nanoscale Structures of Poly(oligo ethylene glycol methyl ether methacrylate) Hydrogels Revealed by Small-Angle Neutron Scattering

The nanostructures of temperature-responsive and biocompatible gels were investigated by small-angle neutron scattering (SANS). The gels were copolymerized using two types of monomers with different ethylene glycol side chain lengths: diethylene glycol methacrylate (MeO(2)MA) (short side chain) and oligo-ethylene glycol methyl ether methacrylate (OEGMA) (long side chain). The temperature-responsive behavior was ascribed to the nanoscale structures and depended on the copolymerization ratio. The SANS profiles of swollen OEGMA-rich gels exhibited a characteristic peak, indicating a strong correlation with the hydrophobic main chain domains in the hydrophilic matrix. The long hydrophilic side chains of OEGMA acted as a cushioning material between the domains. On the other hand, the domains were randomly distributed in the MeO(2)MA-rich gels. As the temperature increased, the domains grew in the gels due to hydrophobic interactions between the dehydrated polymers. As a result, the peaks, that is, the domain periodicity, disappeared in the SANS profiles. The results of this study should lead to a synthesis strategy to control the physical properties and structures of such hydrogels for advanced applications, for example, biofilms, coatings, and carriers.