Thermal degradation mechanism of α,γ-diphenyl alkyl allophanate as a model polyurethane by pyrolysis-high-resolution gas chromatography/FT-IR

Abstract

The thermal degradation mechanism of α,γ-diphenyl alkyl allophanates and carbanilates as model compounds for crosslinking sites in polyurethane networks was investigated by pyrolysis-high-resolution gas chromatography/FT-IR (Py-HRGC/FT-IR). Pyrolysis was performed at 250, 350, 450, and 550 °C. Py-HRGC using a 25 ml capillary column coated with silicone OV-1 followed by FT-IR was carried out. The products were identified by use of a reference system attached to the FT-IR apparatus. The primary degradation reaction was dissociation of allophanate into phenyl isocyanate and alkyl carbanilate, followed by dissociation of the alkyl carbanilate into phenyl isocyanate and alcohol. Decarboxylation of the ethyl carbanilate fragment took also place slowly. A small amount of diphenyl carbodiimide was observed at the pyrolysis temperature of 450 °C. In addition, decarboxylation of the isopropyl carbanilate fragment took place at 550 °C. A small amount of diphenyl carbodiimide was observed from 350 to 550 °C.