Thermoplastic Urethane Chemical Crosslinking Effects

Abstract

This paper reviews the chemical structures and attendant polymer morphology that have been advanced to explain the virtual crosslink (VC) phenomenon in segmented polyurethane elastomers. The different chemical methods employed to produce useful vulcanizates from the classical polyurethane elastomer use-forms (castable liquid, millable gum) through covalent crosslinks (CC) are discussed. And finally, the nature of the polymer property changes occurring when a CC network is superposed on the VC network of a representative thermoplastic poly(ester-urethane) elastomer composition through the use of a free radical curing agent (organic peroxide) is described. The CC-VC network polymer of the subject polyurethane composition proved to have greater resistance to: solvation and its effects, stress relaxation, heat distortion, and compression set, and showed much higher modulus values than the VC network polymer. But the CC-VC network polyurethane also showed less extensibility, tear strength, low temperature flexibility, and flex life. The degrees of these changes are discussed and molecular explanations proposed in some cases.