Polyurethanes
The polyurethanes [126, 132] are sometimes also called "isocyanate polymers." They are characterized by the urethane linkage. Other functional groups, however, may be present in the polymer as well. The urethane linkages can be produced in polymers by several different routes. Among these, the most common ones are through reactions of the isocyanate groups with compounds
bearing hydroxyl groups. Such compounds may be glycols, dihydroxy-terminated polyethers or polyesters, and others. Difunctional reactants will produce linear polyurethanes:
A special method for the preparation of polyurethane polymers was reported [245]. In this new procedure, use is made of "latent" aminimide monomers that are stable and not reactive under normal storage conditions. An example is a monomer, an aminimide, like 1,1,1-trimethylamine 2-(4- hydroxy methylbenzoyl)-imide that undergoes self-polyaddition above 150°C to yield the polyure- thane :
The above monomer can be prepared by reacting methyl para-hydroxymethyl-benzoate with I,1,1- trimethyl hydrazinium p-toluene sulfonate, catalyzed by sodium methoxide. At 170°C, 90% of this monomer converts to polymer in 5 h.
