Oxidative and non-oxidative degradation of a TDI-based polyurethane foam: volatile product and condensed phase characterisation by FTIR and solid state 13C NMR spectroscopy

D. Allan, J. Daly, J.J. Liggat

Research output: Contribution to journalArticle

3 Citations (Scopus)
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Abstract

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.
Original languageEnglish
Pages (from-to)57-73
Number of pages17
JournalPolymer Degradation and Stability
Volume161
Early online date24 Dec 2018
DOIs
Publication statusPublished - 1 Mar 2019

Keywords

  • polyurethane foam
  • TDI
  • solid state NMR
  • condensed phase
  • thermal degradation
  • oxidation

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