Phase diagram for the gelation of temperature-responsive and biocompatible poly(oligo ethylene glycol methyl ether methacrylate) polymers in aqueous free-radical polymerization reactions

In this study, gel-phase diagrams of temperature-responsive and biocompatible polymers were obtained, and the characteristic gelation behaviors of the polymers were examined. The polymers are based on three oligoethylene glycol methyl ether methacrylate (OEGMA) monomers with different numbers of ethylene oxide (EO) units, i.e., with side chains that differ in length. The gelation thresholds depend on the OEGMA and crosslinker concentrations as well as the side chain length. Long EO side chains fill the polymerization system and reduce the concentration of polymer overlap, resulting in a high ability to occupy the system. Furthermore, the EO side chains may engage in self-crosslinking, i.e., polymers can branch and grow from the side chains depending on their length, resulting in a high bond probability. Based on these unique behavior patterns, gelation occurs more readily as the length of the side chains increases. We also synthesized ultralow crosslinked pOEGMA gels by tuning the gelation conditions; these gels exhibited improved swelling capacity and temperature responsiveness. These results should facilitate the development of a synthesis strategy to control the physical properties and structures of these materials for advanced applications, such as biofilms, actuators, and carriers.