Hydrogels Based on Living Ring-Opening Metathesis Polymerization

Abstract

Living ring-opening metathesis polymerization (ROMP) of a hydrophilic norbornene monomer (M4) was performed successfully in air at room temperature using Grubbs’ third generation (G3) catalyst as the initiator. ROMP was then used to copolymerize M4 with a hydrophilic difunctional norbornene cross-linker to develop a rapid and efficient method for preparing hydrogels. Although intramolecular cyclization was observed under dilute conditions, the critical gelation behavior was found to agree with the mean-field theory of Flory and Stockmayer (FS theory) more consistently than that of conventional free radical polymerization systems. By changing the length of the primary polymer chains, the initial molar ratio between monomer and cross-linker, and the length of the cross-linker, the equilibrium swelling ratio and the corresponding mechanical properties of the resultant hydrogels were manipulated across a broad range.