Effects of molecular weight and molecular weight distribution of polyester based soft segments on the physical properties of linear polyurethane elastomers

Linear polyurethane elastomers were synthesized in dimethyl acetamide (DMAc) solution, starting from 4,4′‐methylene diisocyanate 1,4‐butanediol, and polyester diols of two different molecular weights (MW) and each with a series of molecular weight distributions (MWD). Diol samples of various MWD's were prepared by blending polyesters of different MW. Polyurethane elastomer films were cast from solution, and characterized with the effect of the molecular weight and molecular weight distribution of the polyester diols on the physico‐mechanical and morphological properties of the polyurethane elastomers investigated. Most properties studied depended strongly on the MW of polyester soft segments; the MWD influenced primarily the relaxation behaviour of the polyurethane samples. Our data indicates that these phenomena are related to variations of the amounts of high MW polyester diols. The dynamic‐mechanical measurements and the polymer morphology studies indicate that a diffuse, mixed amorphous phase exists in these polymers; the amount of the phase depends on MW and MWD of the polyester segment, but the intrinsic properties are essentially independent of the MWD of the polyester segment.