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Intumescent material, spiro phosphates play an important role in flame retardancy. Several aromatic spiro phosphates were synthesized by reacting 3,9-dichloro-2,4,8,10-teroxa-3,9-diphosphaspiro-5,5-undecane-3,9-dioxide with phenol (SDP), p-cresol (SDPC), 2,6-dimethylphenol (SDDMP) and 2,4,6-trimethylphenol (SDTMP). The chemical structure of the synthesized materials was confirmed by Fourier Transform-Infra Red spectral studies. Pyrolysis GC-MS technique was used to investigate the isothermal degradation (500 °C / 5.0 min) products formed from these spiro phos-phates. Methacrolein, phenol, p-cresol, 2,6-dimethylphenol and 2,4,6-trimethyphenol were observed as the major degradation products. Compared to the evolution of phenol from SDP, the evolution of p-cresol, 2,6-dimethylphenol and 2,4,6-trimethyphenol from SDPC, SDDMP and SDTMP respectively were low. The position and the amount of methyl substitution in the benzene ring have a strong influence on the amount of substituted phenols formed during the pyrolysis. Formation of mono-, di- and tri- methyl substituted phenols from SDP, di- and tri-substituted phenols from SDPC and tri-substituted phenols from SDDMP during degradation can be explained through the formation of phenol-formaldehyde resin type matrix. Identification of several aromatics and condensed aromatics confirmed the isomerisation and polymerization reactions of thermally reactive and highly strained spiro-[2,2]-pent-1,3-diene formed during the pyrolysis of spiro phosphates.