Degradation of phosphorus-containing polyurethanes

Abstract

Copolyurethanes with various phosphorus contents were prepared by copolymerization of tolylene diisocyanate (TDI) with a mixture of polypropylene glocol (PPG), 1,4-butanediol (BN), and phenylbis(hydroxyethyl)phosphonate. The thermal degradation of polyurethane samples was studied by thermogravimetry. It was shown that phenylbis(hydroxyethyl)phosphonate decomposed in the first degradation step. The effect of phosphorus content on thermal stability and activation energy was measured. Two methods of calculation gave activation energies at different stages of the very complex degradation process. The activation energy calculated by the Ozawa method increased with increase in conversion and decreased with increase in phosphorus content. The Flynn method of calculation gave a fairly constant activation energy of about 160 kJ/mol for the first 10% degradation of the phosphorus-containing polyurethanes. Polyurethanes with higher phosphorus content display lower onset temperature of degradation, lower activation energy and higher char yield.