Biodegradable Poly(ester-urethane-amide)s Based on Poly(ε-caprolactone) and Diamide-Diol Chain Extenders with Crystalline Hard Segments. Synthesis and Characterization

Twenty seven poly(ester-urethane-amide)s (PEUAs) were synthesized from the reaction of alpha,omega-telechelic poly(epsilon-caprolactone) dials, 1,6-hexamethylene diisocyanate, and three different diamide diol chain extenders derived from epsilon-caprolactone and three aliphatic diamines with increasing length (n = 2, 4, and 6). The hard segment (HS) was designed to be crystalline and to introduce amide groups, more susceptible to hydrolysis than urethane or urea groups. Crystallization of the HS was achieved even at very low HS content, leading to a phase-separated material. Furthermore, HS crystallinity recovered from the material homogeneous melt on cooling. Thermal degradation was well above HS melting point, allowing for melt processing of these materials. HS melting point was affected by HS content, poly(epsilon-caprolactone) diol length, and chain extender length. The length scale of the phase-separated morphology lied in between 11 and 13 nm up to similar to 60% HS content and decreased at higher HS content values. HS content was the main parameter affecting the mechanical properties. The prepared PEUAs degraded hydrolytically at very long times by surface erosion.