High performance of interpenetrating polymer network hydrogels induced by frontal polymerization

We report the rapid synthesis of hydrogels with interpenetrating polymer networks (IPNs) by frontal polymerization (FP). Appropriate amounts of diacetone acrylamide (DAAM), N-methylolacrylamide (NMA), thermoplastic polyurethane (TPU), N,N'-methylenebisacrylamide (MBAA), and ammonium persulfate (APS)/N,N,N',N'-tetramethylethylenediamine (TMEDA) were mixed together at ambient temperature. FP was initiated by transitorily heating the upper side of the reactants, and poly(DAAM-co-NMA)/TPU IPN hydrogels were obtained within minutes. The preparation parameters were thoroughly investigated. Moreover, we investigated the morphology, swelling capacity, chemical structure and the mechanical properties of poly(DAAM-co-NMA)/TPU IPN hydrogels, along with those of poly(DAAM-co-NMA) hydrogels without IPN structure for comparison. Interestingly, the mechanical strength of poly(DAAM-co-NMA)/TPU IPN hydrogels is notably improved in comparison with that of poly(DAAM-co-NMA) hydrogels. The results indicate that the IPN structure endows hydrogels with high mechanical strength, and FP can be applied as an alternative means for synthesis of IPN hydrogels with additional advantages of speed and efficiency.