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

Polyurethanes (PUs) prepared by varying the hard-to-soft segments ratio, and the chain extender 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-hexanediol 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 systematically 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 significantly 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.