Traditionally TDI prepolymers are cured with amines and MDI prepolymers with diols. Amine cures have not been used with MDI prepolymers due to high reactivity (short pot life) even though they offer some performance advantages such as high temperature resistance and tear properties. New Adiprene MDI prepolymers with low free monomer content (LF MDI) prepolymers cured with tris (4,4’-diaminodiphenyl methane) sodium chloride (TDDM) provide a superior hard segment and offer some unique processing and productivity improvements. The superior hard segment obtained by curing LF MDI prepolymers with TDDM offers excellent physical and engineering properties, including high cut and tear resistance, improved flex fatigue, low temperature flexibility, excellent dynamics (at both low and high temperatures) and other high temperature properties. It also offers EH&S advantages as it is based on low free monomer technology and is a MBOCA free system