Synthesis of hydrogels viaring-opening metathesispolymerization: factors affecting gelation

Ring-opening metathesis polymerization (ROMP) was used to synthesize hydrogels via copolymerization of a diamine monomer 3 and a novel cross-linker 5 using Grubbs' third generation catalyst as initiator. Reactions were performed at two different monomer concentrations and at various initial molar ratios of cross-linker to initiator. At low monomer concentration, gelation occurred at initial cross-linker to initiator ratios of 1.5 and greater, which decreased to values of 1.05 and greater when increasing the monomer concentration. This result is in agreement with the Flory–Stockmayer theory. The gel yield and swelling properties were also found to be dependent on the cross-linker to initiator molar ratios. GPC data of the sol fractions showed quantitative consumption of both the monomer and the cross-linker. The molecular weight of the sol fraction was independent of the initiator concentration at constant cross-linker concentration of 2.5 mol%. Gels were found to swell up to 72 times their weight in 0.9% NaCl solution.