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Hydrogels based on either butyl acrylate or its isomer (tert. butyl acrylate) and acrylic acid cross-linked with 4,4’-di (methacryloylamino)azobenzene (DMAAB) were fabricated using organic-redox-initiated radical copolymerization technique at an ambient temperature. The organic redox co-initiator system comprises N-phenyldiethanolamine and benzoyl peroxide. The hydrogels were pH-responsive: the equilibrium swelling ratios of the hydrogels were very low at pH 2.0 (simulating the condition in the stomach); the hydrogels swelled exensively at pH 7.4 (stimulating the condi-tion in the intestine). The equilibrium swelling ratios of the hydrogels incresed with the concentration of the co-initiator system. The molar ratios in which N-phenyldiethanolamine and benzoyl peroxide (the co-initiator system) combined affacted the equilibrium swelling ratio: the equilibrium water content increased with increase in the molar concentration of the amine at a fixed concentration of benzoly peroxide. Hydrogels prepared with butyl acrylate gave higher equilibrium swelling ratios than corresponding hydrogels prepared with tert. butyl acrylate under the same conditions. The organic-redox-initiated radical copolymerization technique appears suitable for synthesizing hydrogels for use in colon-specific delivery of thermolabile drugs like peptides and proteins.