Structural Basis for Intumescence ― Study of Model Compounds Containing Spiro Phosphorus Moiety and Polymers Containing Such Units

摘要

Spiro phosphorus compounds play a vital role, in recent years, in imparting flame retardancy and intumescence to the polymers. To ascertain the mechanism of the intumescency, model spiro phosphorus compounds, i.e., 3,9-disubstituted-2,4,8, 10-tetraoxa-3,9-diphosphaspiro-[5.5]-undecan- 3,9-dioxide, were chosen (compound Ⅰ : substitution is chloro group and compound Ⅱ : substitution is hydroxo group). The model compounds were investigated using Differential Thermal Analysis (DTA) and Thermal Volatilization Analysis (TVA), Vacuum Pyrolysis-MS and Off-line Pyrolysis followed by degradation product analysis by GC-MS. Dichlorospiro compound (Ⅰ) showed an eruptive release of gases at 320 ℃ and dihydroxo spiro compound (Ⅱ) at about 350℃. The major components of the gas released were found to be HCl and H_2O in the case of compound Ⅰ and H_2O in the case of compound Ⅱ. The degradation product analysis showed the formation of wide varieties of substituted and condensed aromatic compounds in measurable quantities. From the acquired data, it is confirmed that the intumescence takes place within a narrow range of temperature (10°) and in this temperature limit extensive dehydrohalogenation and dehydration are taking place. Highly thermally reactive unsaturated hydrocarbons are produced which mainly undergo polymerization to aromatic compounds and finally to char.