Effect of Soft Segment Polydispersity on the Elasticity of Polyurethane Elastomers

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) (PTMO₆₅₀, PTMO₁₀₀₀, and PTMO₂₀₀₀). To obtain a narrow soft segment molecular weight distribution, fractionated samples of PTMO₁₅₄₆ 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