Miscibility,morphology and mechanical properties of rubber‐modified biodegradable poly(ester‐urethanes)

Biodegradable, lactic acid based amorphous poly(ester‐urethane)s (PEU) were modified with poly(L‐lactic acid‐co‐ϵ‐caprolactone‐urethane) elastomer (P[LA/CL]U) by melt blending. The phase separation of P(LA/CL)U elastomer with three different ϵ‐caprolactone (CL) compositions (CL content 30, 50, and 70 mol %) and the mechanical properties of the resulting impact‐modified linear and branched PEU were investigated. The amounts of P(LA/CL)U elastomer in the PEU blends were 10, 15, 20, and 30 wt %. Dynamic mechanical thermal analysis (DMTA) of the blends with P(LA50/CL50)U and P(LA30/CL70)U elastomers revealed separate glass transition temperatures for rubber and matrix, indicating phase separation. No phase separation was found for P(LA70/CL30)U elastomer. The effect of mixing rate and temperature during processing on composite properties was tested by blending P(LA30/CL70)U rubber with PEU under various processing conditions. Impact modification studies were also made with two P(LA30/CL70)U elastomers having different amounts of functional groups. The influence of end‐functionalization and cross‐linking on mechanical properties was investigated in blends containing PEU and 15 wt % of these elastomers. Scanning electron microscopy (SEM) showed the morphology to change dramatically with increase in the degree of cross‐linking in the rubber. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1074–1084, 2000