Biodegradable and pH‐sensitive hydrogels: Synthesis by crosslinking of N,N‐dimethylacrylamide copolymer precursors

Abstract Novel pH‐sensitive hydrogels containing azoaromatic crosslinks were synthesized by the crosslinking of polymeric precursors. First, a reactive polymeric precursor was synthesized by copolymerization of N,N‐dimethylacrylamide, N‐tert‐butylacrylamide, acrylic acid, and N‐methacryloylglycylglycine p‐nitrophenyl ester. The hydrogel was prepared in the second step by the reaction of the polymeric precursor with N,N′‐(ω‐aminocaproyl)‐4,4′‐diaminoazobenzene. The hydrogels were characterized by the network structure, (that is, content of crosslinks, unreacted pendent groups, and cycles), the equilibrium swelling ratio as a function of pH, modulus of elasticity in compression, and the degradability in vitro. The results obtained indicated that the hydrogel network structure strongly depends on the reaction conditions such as polymer concentration, and the ratio of the reactive groups during the crosslinking reaction. The swelling and mechanical properties of hydrogels can be controlled by the modification of polymer backbone structure and/or the crosslinking density. The rates of hydrogel degradation depended on their degree of swelling. The higher the degree of swelling, the higher the degradability. The properties of the hydrogels suggest that they have a potential as carriers for colon‐specific drug delivery. © 1994 John Wiley & Sons, Inc.