Thermoplastic Polyurethane Elastomers Made from High Molecular Weight POLY-L® Polyols

Abstract

High molecular weight polyether polyols formed by the poly merization of epoxides, especially propylene oxide, using conventional KOH catalysis contain high levels of unsaturation. This unsaturation is in the form of allyl and isopropenyl end groups and results in a loss of functionality. A diol that ideally has a functionality of 2.0 can be as low as 1.70 for a conventional 4000 molecular weight polyol. As the molecular weight increases the func tionality decreases. Since the unsaturation is a function of molecular weight, a limiting molecular weight will be reached where further propylene oxide fails to add to the chain and to increase molecular weight.

High molecular weight polyether diols containing low unsaturation were pre pared using double metal cyanide catalysts. With these catalysts ultra high molecular weight polyols can be made without a concomitant increase in the rate of formation of unsaturated end groups. A 4000 molecular weight diol was made that had unsaturation levels five times lower than a comparable polyol prepared by conventional KOH catalysis. Additionally, 5500 and 6600 molec ular weight diols containing very low unsaturation levels were also made. All of the polyols were capped with ethylene oxide to give high levels of primary hydroxyl groups. These polyols were evaluated in thermoplastic polyurethane elastomer formulations.

The thermoplastic polyurethane elastomers were based on MDI and chain ex tended with butanediol. Those prepared from polyols with low unsaturation levels had significantly higher physical properties than thermoplastic polyurethane elastomers prepared with conventionally made polyols. Soft ther moplastic polyurethane elastomers were made from high molecular weight polyols containing low unsaturation levels. These soft thermoplastic polyure thane elastomers are softer than any currently commercially available. They exhibited good tensile strength, excellent elongation and high resilience prop erties.

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