Transport-morphology relationships in segmented polybutadiene polyurethanes: 2. Analysis

An analysis of the transport properties in a series of segmented polybutadiene polyurethanes described in Part 1 is presented in terms of the effective medium theory (EMT) and simple transport models involving ordered microstructures. The 75 wt% hard segment (HS) sample is assigned a dispersed morphology of soft segment (SS) spheres in a glassy matrix of hard segment. A lamellar morphology is indicated at 55 wt% HS by all methods of analyses: TEM, SAXS and transport models. Based on sorption studies and the results from SAXS, cylindrical domains of hard segment in a rubbery matrix of soft segment are believed to exist in the dilute range (< 40 wt%) of hard segment content. Complex sorption kinetics indicate the inadequacy of Fick's law to describe the transport in copolymer samples of rubbery and glassy materials. Relaxational effects dominate the transport of CO₂ in polybutadiene polyurethanes. In this case, a simple transport model using EMT involving coupled diffusion and relaxation is used to describe the anomalous sorption kinetics.