| Abstract: | The microdomain structure of a series of segmented polyurethane block copolymers is characterized by small-angle x-ray and neutron scattering analyses. The materials contain hard segments formed from 4,4′- diphenylmethane diisocyanate (MDI) and butanediol (BD), and range in hard-segment content from 20 to 80% by weight. The results provide evidence for a transition from discrete to continuous hard-microdomain morphology as the hard-segment content is increased above ca. 50%. The measured concentration dependences of the interdomain spacing, specific interfacial area, diffuse microphase boundary thickness, and scattering invariants are used to examine the validity of present models for hard-microdomain structure. The observed behavior corresponds well with the general predictions of a lamellar model wherein partially coiled hard-segment sequence configurations are allowed. The thickness of the hard microdomains extracted from the model corresponds to approximately four hard-segment repeat units. Scattering invariant calculations are used together with determinations of the soft-microphase glass transition temperatures to examine possible models for microdomain mixing. These calculations suggest that both the hard and soft microphases are phase mixed. |
