Tissue-compatible multiblock copolymers for medical applications, controllable in degradation rate and mechanical properties

A class of degradable, phase-segregated multiblock copolymers is presented. The new copoly(ester-urethane)s, termed DegraPol(TM)/btgc, consist of crys tallizable poly[(3-R-hydroxybutyrate)-co-(3-R-hydroxyvalerate)]-segments an d amorphous segments from epsilon-caprolactone, diglycolide and ethylene gl ycol. As junction unit an aliphatic diisocyanate, TMDI, is applied. The cop oly(ester-urethane)s are thermoplastic elastomers (T-m = 120-136 degrees C) and are processable without degradation. For medical applications, materia ls are needed in which the degradation rate and the mechanical properties a re independently adjustable to the medical needs. The mechanical properties of DegraPol(TM)/btgc, e.g., elasticity and toughness, can be controlled by the weight fraction of crystallizable segment; the elastic moduli of Degra Pol/btcg are adjustable between 50 MPa and 500 MPa and were only little inf luenced by the chemical structure and the composition of the soft segment. By insertion of 'weak links' in the form of easily hydrolyzable glycolyl-gl ycolate ester bonds into the amorphous segments, we attempted to synthesize degradable polymers in which the hydrolytic degradation rate can be contro lled by the amount and the sequence distribution of these bonds. We report on the synthesis and on the thermal and mechanical properties of such polym ers.