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Three poly(beta-aminoester)s with pendant primary amines were synthesized by Michael addition of N-Boc-protected diamine to 1,4-butanediol diacrylate, followed by removal of N-Boc-protective group under anhydrous acidic conditions. The degradation rate of poly(beta-aminoester)s with pendant primary amines is dependant on their side-chain structures and pH value of incubation buffer. The degradation in basic environments is much faster than in acidic environments. The degradation of poly(beta-aminoester) with pendant primary amine involves intramolecular/intermolecular amidation and hydrolytic degradation. Under physiological conditions, the intramolecular/intermolecular amidation of poly(beta-aminoester) plays an important role in the polymer degradation. Polymers 1a-1c show significant buffer capacity at pH 4-10. The cytotoxicity of polymer la is Much higher than that of polymers 1b and 1c.