Synthesis of degradable, biocompatible, and tough block-copolyesterurethanes

We describe the synthesis of micro-phase-segregated block-copolyesterurethanes from telechelic hydroxyterminated poly{[(R)-3-hydroxybutyric acid]-co-[(R)-3-hydroxyvaleric acid]} (PHB-diol) as ''hard segments'' (i.e., crystallizable chain sections) and hydroxyterminated poly(epsilon-caprolactone)-diethylene glycol-poly(epsilon-caprolactone) (PCL-diol) or telechelic hydroxyterminated poly[(adipic acid)-alt-(1,4-butanediol; diethylene glycol; ethylene glycol)] (Diorez(R)) as ''soft segments'', with 2,2,4-triethylhexamethylene diisocyanate (TMDI) or methyl (S)-2,6-diisocyanatohexanoate (LDI). High molecular weights were obtained with or without catalyst, the properties of the polymers depending only slightly on the presence or absence of the catalyst. The materials thus obtained were investigated also with respect to their mechanical properties and it was found that Young's modulus directly depends on the fraction of crystallizable PHB-diol in the block copolymer while the type of non-crystallizable segment or diisocyanate had only a minor influence: Generally, the tensile strength increases and the elongation at break decreases with increasing content of PHB-diol. Around body temperature, these polymers exhibit only mild changes in their mechanical behavior. The chain length of the non-crystallizable segment indirectly influences the morphology and the mechanical properties of the polymers through changes in the phase-segregation behavior.