A family of copolyurethane elastomers was synthesized, based on 1,4-butanediol (BDO) or diethylene glycol (DEG) and hard segments of 4,4′-dibenzyl diisocyanate (DBDI) of constant uniform length. The materials had comparable molecular weights. The soft-segment (SS) polydispersity was varied. A broad polydispersity was achieved by blending polyols of different molecular weights of poly(oxytetramethylene) (PTMO 650 , PTMO 1000 , and PTMO 2000 ). To obtain a narrow soft segment molecular weight distribution, fractionated samples of PTMO 1546 were prepared. The tensile and thermomechanical properties were determined. Results were related to microstructural changes, on the basis of evidence from wide-angle X-ray scattering (WAXS). Increasing the SS polydispersity from 1.1 to 1.72 resulted in an improvement of the mechanical properties. Inelastic effects were most pronounced when the hard segment crystallized and in the case of the materials achieved with a narrow SS polydispersity.

A family of segmented polyurethane elastomers (SPUs) was synthesized. Hard segments were chosen to be generated from two isocyanates: the rigid 4,4-diphenylmethane diisocyanate (MDI) and the flexible 4,4-dibenzyl diisocyanate (DBDI), alone or as mixtures. A polyester soft segment polyethylene adipate of molar mass 2000 g mol À1 and a small molecule chain-extender diol, ethylene glycol, were used. Hard segment fraction was maintained at B40%. The structure-property relationship of SPUs was investigated using several characterization techniques. Morphological features such as interdomains of the soft and hard segments were identified by means of atomic force microscopy. The thermal and mechanical behavior was evaluated by using dynamic mechanical analysis, differential scanning calorimetry and uniaxial tensile tests. Structural changes induced by varying the type and the number of isocyanates and the order of their introduction were also followed by using wide-angle X-ray. Materials with hard segments based on the single diisocyanate DBDI were observed to crystallize. Crystallinity was strongly reduced when DBDI was mixed with MDI. Improvement in elastomeric properties was obtained when both diisocyanates were included and reacted together in a random manner.

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