The oxidative and non-oxidative degradation behaviour of a flexible polyurethane foam, synthesised from toluene diisocyanate and a polyether polyol, is reported. Both toluene diisocyanate and diaminotoluene were identified as major products under non-oxidative conditions, which indicates that the urethane linkages are degrading by two competing degradation mechanisms. Degradation of the urethane linkage by a depolymerisation reaction to yield toluene diisocyanate and polyol is proposed to occur initially. In addition, the atmospheric pressure conditions favour the degradation of the urethane linkages via a six-membered ring transition state reaction to form diaminotoluene, carbon dioxide and alkene terminated polyol chains. Solid-state 13C NMR spectroscopy and elemental analysis of the residues indicates that at temperatures above 300°C ring fusion of the aromatic components within the foam occurs, and this leads to a nitrogen-containing carbonaceous char which has a complex aromatic structure. It is proposed that under the confined conditions of the degradation the aromatic nitrogen-containing species, such as toluene diisocyanate and diaminotoluene, undergo secondary reactions and ring fusion to yield a complex char structureUnder oxidative conditions, degradation, including ring fusion, occurs
at a lower temperature than under non-oxidative conditions. Neither
toluene diisocyanate nor diaminotoluene were observed as major
degradation products. The polyol is observed to undergo thermo-oxidative
degradation at much lower temperatures than purely thermal degradation.
As a consequence, the depolymerisation reaction via the
six-membered ring transition state is limited in extent and
diaminotoluene is not evolved. The absence of toluene diisocyanate is
proposed to be a result of this species undergoing oxidative degradation
reactions which lead to it being incorporated into the char.
- polyurethane foam
- solid state NMR
- condensed phase
- thermal degradation