Thermal degradation of the polyurethane from 1,4-butanediol and methylene bis(4-phenyl isocyanate)

A polyurethane prepared from 1,4-butanediol (BD) and methylene bis(4-phenyl isocyanate) begins to evolve volatile degradation products at approximately 240°C. By a combination of thermal analysis methods (TVA, TG, and DSC) and examination of the volatile and involatile products by using a combination of GLC and infrared and mass spectrometric analysis, it is shown that the total reaction comprises a primary depoly-condensation process in which the two monomers are formed, followed by the subsequent reaction of these monomers to form the volatile products, tetrahydrofuran, dihydrofuran, carbon dioxide, water, butadiene, hydrogen cyanide, and carbon monoxide and residual carbodiimide and urea structures. A mechanism, which accounts for all these products, has been formulated and tested.