Influence of the type of chain extender and urethane group content on the mechanical properties of polyurethane elastomers with flexible hard segments

A study was made of how aspects of the mechanical response of polyurethane elastomers (PUs) based on poly(ethylene adipate) (PEA) vary with the number of CH₂ methylene groups when using chain extenders of the type HO–(CH₂)_p–OH. The effect of varying the odd–even number of CH₂ groups in regard to the chain extender was followed. The best mechanical behavior as elastomers was revealed for polyurethanes with CH₂ even numbers on the chain extender, when the different parts of the PUs macromolecular chains can adopt extended linear forms. The effect of different concentrations of the hard segment content on a set of PUs based on PEA and 1,4-butanediol as chain extender was also studied. A hitherto overlooked isocyanate of variable geometry, 4,4′-dibenzyl diisocyanate was used in the PUs synthesis, based on a –CH₂CH₂– spacer group between the two aromatic rings.