Effect of the hard segment chemistry and structure on the thermal and mechanical properties of novel biomedical segmented poly(esterurethanes)

Two series of biomedical segmented polyurethanes (SPU) based on poly(epsilon-caprolactone) diol (PCL diol), 1,6-hexamethylene diisocyanate (HDI) or l-lysine methyl ester diisocyanate (LDI) and three novel chain extenders, were synthesized and characterized. Chain extenders containing urea groups or an aromatic amino-acid derivative were incorporated in the SPU formulation to strengthen the hard segment interactions through either bidentate hydrogen bonding or pi-stacking interactions, respectively. By varying the composition of the hard segment (diisocyanate and chain extender), its structure was varied to investigate the structure-property relationships. The different chemical composition and symmetry of hard segment modulated the phase separation of soft and hard domains, as demonstrated by the thermal behavior. Hard segment association was more enhanced by using a combination of symmetric diisocyanate and urea-diol chain extenders. The hard segment cohesion had an important effect on the observed mechanical behavior. Polyurethanes synthesized using HDI (Series H) were stronger than those obtained using LDI (Series L). The latter SPU exhibited no tendency to undergo cold-drawing and the lowest ultimate properties. Incorporation of the aromatic chain extender produced opposite effects, resulting in polyurethanes with the highest elongation and tearing energy (Series H) and the lowest strain at break (Series L). Since the synthesized biodegradable SPU possess a range of thermal and mechanical properties, these materials may hold potential for use in soft tissue engineering scaffold applications.