Synthesis of hydrogels via ring-opening metathesis polymerization: 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. Ring-opening metathesis polymerization (ROMP) was used to synthesize hydrogels from an amine containing monomer. At 1.28 M monomer the results were in close agreement with the Flory-Stockmayer theory. These novel cationic gels were found to swell up to 72 times their weight in 0.9% NaCl solution.