SAXS ANALYSIS OF A LINEAR POLYESTER AND A LINEAR POLYETHER URETHANE - INTERFACIAL THICKNESS DETERMINATION.

Linear segmented polyurethanes are thermoplastic copolymers that generally display a considerable degree of elastomeric behavior. They also typically have a ″domain″ morphology that arises from the thermodynamic incompatibility of the two types of segments that comprise the chain. The extent of phase separation as well as the mechanical properties depend on many factors including the chemistry and compatibility of the ″soft″ and ″hard″ segments, composition ratio, molecular weight and the distribution of each component as well as thermal history. The common soft segments used for commercial applications are either polyethers or polyesters having a molecular weight in the range of 800-2000. One of the important differences between the polyester and polyether soft segments is their affinity for the hard segments. In this paper results of an experimental study which show that polyether urethanes display a lower degree of interfacial mixing than does a polyester urethane. However, caution must be exercised in over interpreting these data for due to the nature of domain structure in these materials, the interfacial layer is likely non uniform over the domain due to ordering (segment alignment) within the domains. This ordering process within domains is in great contrast to the domain structure of the well known ABA block copolymers as styrene-butadiene where no such ordering occurs thereby likely giving rise to a uniform interfacial layer over the entire domain surface.