Diels-Alder reaction in water for the straightforward preparation of thermoresponsive hydrogels

Because the properties and applications of hydrogels are determined by the formation principle and conditions of the hydrogels, novel methods for preparing hydrogels have increasingly triggered scientists' interest. Here the Diels-Alder reaction was applied to the preparation of hydrogels. For the resultant polymeric diene and dienophile, the Diels-Alder reaction could be performed in water. The gelation time was found to be closely related to the temperature. The gelation time decreased with the temperature increasing. Moreover, the hydrogels were stable in water, and the retro-Diels-Alder reaction could be performed in N,N-dimethylformamide easily. A study of the swelling ratio indicated that the hydrogels were responsive to the temperature. The hydrogel formation method described here provides several advantages, such as mild reaction conditions, no initiator or catalyst, a tunable gelation rate, and thermal reversibility, and it has great potential for the preparation of biomaterials.