Structure-property relationships for the design of polyiminocarbonates.

Structure-property relationships for the design of new polyiminocarbonates were established, based on the investigation of thermal stability and processibility, morphology, tensile strength, hydrolytic degradation and drug release profiles of 15 different polyiminocarbonates. The results indicated that some polyiminocarbonates were among the mechanically strongest, bioerodible polymers currently available. The iminocarbonate bond was highly unstable under physiological conditions, facilitating the design of rapidly degrading devices. The drug-release profiles of certain polyiminocarbonates exhibited lag periods, facilitating the design of pulsed-release or delayed-release devices. Possible limitations of the practical applicability of polyiminocarbonates as biomaterials were the low thermal stability of the iminocarbonate linkage and the complicated, two-phase degradation mechanism that led to the formation of slowly degrading residues of low molecular weight. To identify non-toxic diphenols as monomers for the synthesis of polyiminocarbonates, derivatives of tyrosine dipeptide were systematically explored. Using structure-property relationships as design guidelines, desaminotyrosyl-tyrosine hexyl ester was identified as a promising, tyrosine-derived diphenol. The corresponding poly(desaminotyrosyl-tyrosine hexyl ester iminocarbonate) formed amorphous, transparent films and was mouldable at about 70 degrees C. It had a tensile strength of 400 kg/cm2 and a tensile modulus of 16,300 kg/cm2. Under physiological conditions in vitro, a thin film made of high molecular weight poly(desaminotyrosyl-tyrosine hexyl ester iminocarbonate) degraded to low molecular weight oligomers within 5 d. The results indicated that polyiminocarbonates and in particular poly(desaminotyrosyl-tyrosine hexyl ester iminocarbonate) might be of interest in a variety of biomedical applications.