Relationship between Chemical Composition and Hysteresis in Polyurethane Elastomers

Abstract

Polyurethane elastomers have been prepared from 1,4-cyclohexane- diisocyanate, hydroxy terminated poly(tetramethylene oxide), 1,4-butanediol and trimethylolpropane. Selected sample blocks (63.5 × 63.5 × 15.9mm) have been tested for hysteretic heat build-up during compressive cycling. During 200,000 cycles at 18.5 Hertz under a maximum load of 24.5 kg and a ratio of minimum load to maximum of 0.1, the internal temperatures for different samples ranged from 50 to 160°C. Thermomechanical analysis indicates final softening values of 250°C for most samples. Mechanical properties are maintained up to at least 180°C in dynamic mechanical analysis. The samples have low weight percents of hard segment, approximately 20 percent, but have high Shore A hardness values in the 80-90 range. Trouser tear strengths range from 4kN/m for a heavily crosslinked sample to 30 kN/m for a linear sample. The low internal temperature generated during compressive fatigue testing, as well as other exceptional properties of these polyurethanes are attributed to the compact nature of the diisocyanate and its ability to form very small hard segment crystallites with melting temperatures above 200°C.