Effect of Composition and Hard-segment Content on Thermo-mechanical Properties of Cross-linked

Abstract: Polyurethanes (PUs) prepared by varying the hard-to-soft segments ratio, and the chain exten-der size and nature were studied. Polyurethane cross-linked copolymers composed of 4,4-methylenebis-(phenylisocyanate), poly(ethylene adipate)diol, and glycerine, 1,3 propanediol, 1,4-butanediol, 1,6-hexa-nediol as a chain extender were synthesized by a two-step process. In the present study, cross-linked poly(ester-urethanes) were prepared with hard segment contents from 22 to 44 % by weight, by systemat-ically varying the ratio of the hard-segment extender. Hard segment content has a significant influence on the mechanical and thermo-mechanical properties of PUs, such as maximum stress, tensile modulus, and elongation at break. In particular, maximum stress, tensile modulus, and elongation at break increased sig-nificantly at 24 wt. % of hard segment content. Interchain crosslinking improves thermal stability, which was measured by thermogravimetric analysis and differential scanning calorimetry. In contrast with glassy shape memory polymers, chemically cross-linked polyurethane behaves as an elastomer capable of shape memory. Key Words: Polyurethane elastomers, chain extender, cross-link, hard segment, mechanical properties 1