A comparison of phase organization of model segmented polyurethanes with different intersegment compatibilities

Three series of chemically well-defined polyurethanes were synthesized with the same hard segments but different soft-segment chemistries of interest in biomedical applications. The multiblock polyurethanes have soft segments composed of either an aliphatic polycarbonate [poly(l,6-hexyl 1,2-ethyl carbonate)], polytetram- ethylenoxide, or a mixed macrodiol of polyhexamethylenoxide and hydroxyl-terminated poly(dimethylsiloxane) and the same hard-segment chemistry [4,4′-methylenediphenyl diisocyanate and 1,4-butanediol]. Analysis using small-angle X-ray scattering and other methods demonstrates that demixing of the hard and soft segments varies greatly between the three series of copolymers. For example, the PDMS/PHMO-based copolymers exhibit a three-phase, core - shell morphology, while the other two series exhibit a typical two-phase structure. In addition to quantitative measurements of hard/soft-segment demixing for the two-phase copolymers, FTIR spectroscopy was used to assess inter- and intracomponent hydrogen bonding, and tapping mode AFM was used to characterize the nanoscale morphology.