No abstract

The microphase-separated morphology in a series of well characterized polybutadiene polyurethanes with hydroxy-terminated polybutadiene (HTPBD) endcapped with 2,4-toluene diisocyanate (TDI) as the soft segment (SS) phase, and the combination of 2,4-toluene diisocyanate and 1,4-butanediol (BDO) as the hard segment (HS) phase, has been investigated by transmission electron microscopy (TEM) and sorption studies using N 2 , 0 2 and C0 2 • This system constitutes a model segmented polyurethane copolymer composed of amorphous rubbery and glassy domains. Evidence for the presence of phase separation is inferred from the scattering and phase contrast mechanisms of imaging. However, it is not possible to assign specific domain morphologies such as spherical, lamellar or cylindrical, based solely on the results of TEM. Complementary evidence of the domain presence is provided from the transport results; in particular, phase inversion and domain connectivity. Incomplete phase separation was indicated from the combined transport-morphology results for samples with less than 33 wt% hard segment.

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 ofC0 2 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.