Soft-segment phase domain

Note Soft-segment phase domains are often larger than hard-segment phase domains and are often continuous. 

Note The types of domain in a segmented copolymer usually comprise hard- and soft-segment phase domains. 

Sometimes, copolymers with many, but short blocks, are named segmented copolymers (multiblock copolymers). Segmented copolymers contain phase domains of microscopic or smaller size. The domains constituted principally of single types of stmctural unit. Typically, a segmented copolymer comprises hard-and soft-segment phase domains. 

Figure 1. Molecular schematics of some possible segmented polyurethane morphologies. For convenience, good phase separation is assumed, (a) Hard-segment domains dispersed within a soft-segment matrix (b) interconnected hard-segment phase giving rise to continuous phases of both hard and soft segments (c) soft-segment phase is dispersed within a continuous matrix of hard segments.

The sane compatibility/incompatibility rules as discussed for amorphous hard segments and soft segments do not apply with crystalline hard segments. Extenders which form crystalline hard segments with MDI aggregate into bundles or form a hard segment domain within the amorphous soft segment phase (3). 

Proton spin-temperature equilibration between the hard- and soft-segment-rich domains of the polyurethane elastomer on the order of 10-100 ms might be considered fast relative to a macroscopically phase-separated blend [26] or copolymer, but slow relative to a strongly interacting mixture [25]. This is reasonable for a microphase-separated material whose solid state morphology has been the subject of considerable theoretical and experimental research. Under fortuitous circumstances, intimate (near-neighbor) contact between dissimilar molecules in a mixture can be studied via direct measurement of proton spin diffusion in a two-dimensional application of the 1H-CRAM PS experiment (Combined Rotation And Multiple Pulse Spectroscopy). Belfiore et al. [17,25,31] have detected intermolecular dipolar communication in a hydrogen-bonded cocrystallized solid solution of poly(ethylene oxide) and resorcinol on the f00-/xs time scale, whereas Ernst and coworkers [26] report the absence of proton spin diffusion on the 100-ms time scale for an immiscible blend of polystyrene and poly(vinyl methyl ether), cast from chloroform. 

PU elastomers contain alternative soft and hard segments, which separate into different phases. Hard domains play a role of cross-links, whereas soft blocks provide extensibility. Therefore, morphology and properties of PU are defined by relative amount of soft and hard segments. For example, at 70% concentration of soft segments, the material is described as a mbbery matrix with... 

---