1,2-Bis(2-oxo-azepane-1-carboxylic acid-p-phenyl-amide)ethane and 1-(2-Oxo-azepane-1-carboxylic Acid-o-phenyl-amide)-2-(2-oxo-azepane-1-carboxylic acid-p-phenyl-amide)ethane

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Hard Segment Inelastic Effects on the Stress-Strain Response of Polyurethane Elastomers Based on Hard Segments of Variable Geometry

A study was made of a family of thermoplastic polyurethane copolymers, in which the nature and number of the hard segment components (crystallizing or not) were varied. Materials were synthesized with ethylene glycol (EG) as chain extender. Changes induced by varying the type and the number of isocyanates and the order of their introduction were followed and the mechanical responses were measured in cyclic tensile tests and stress relaxation in interrupted tests. Polymers based on DBDI hard segments showed lower strain recovery and strain energy recovery on cycling than did the conventional materials with MDI and the materials based on mixtures of isocyanates MDI/DBDI. Such features of the response were attributed to differences in hard phase plastic flow stress; hard domain hydrogen bonding exerted strong influences on the inelasticity of polyurethane elastomers. Stress-strain cycles reflected the resistance to plastic deformation occurring in the hard domains. This was enhanced by more pronounced hydrogen bonding achieved in the more mobile DBDI than in MDI. Copyright © Taylor and Francis Group, LLC