Effect of curative and stoichiometry on the hysteresis in polyurethane‐ureas

Hysteresis in the fifth loading cycle has been measured for a series of polyurethane-ureas based on polytetramethylene glycol (PTMEG), toluene diisocyanate (TDI), and two different amine chain extenders/curatives, methylenebisortho chloroanaline (MBOCA) and a dimethylthio toluene diamine (Ethacure 300, Ethyl Corp.). Hysteresis was seen to increase with strain and temperature in all samples. However, the increase in hysteresis with strain was limited by crosslinking of the hard domains and these materials also showed decreased temperature dependence at higher temperatures. These results are discussed in terms of the structure of the polymers and possible mechanisms leading to hysteresis.