Thermal degradation mechanism and rate constants of the thermal degradation of poly(epichlorohydrin- co-ethylene oxide), deduced from pyrolysis-GC-MS studies

Abstract

The thermal degradation mechanism and kinetic parameters for the overall degradation for the poly(epichlorohydrin- co-ethylene oxide) elastomer have been investigated by pyrolysis-gas chromatography-mass spectrometry (pyrolysis-GC-MS) techniques. In this study the total volatile products from the pyrolysis of the elastomer at different temperatures were measured as a Total Ion Current (TIC) in the mass spectrometer. Information about the components within the TIC was obtained from measurements of the Selected Ion Currents (SIC) of ions of different m/z ratios. Amongst the m/z ratios observed, those corresponding to ions of m/z of 35, 36, 37, and 38 confirmed that HCl is one of the pyrolysis products. SIC measurements for a wide range of other possible degradation products were examined in order to assess the general structures, and these revealed that a wide range of low molar mass hydrocarbons and chlorohydrocarbons are formed on thermal degradation of the elastomer. The results suggest that a major mechanistic process is the depolymerization of macroradicals, and that hydrogen abstraction from a carbon atom adjacent to a C–O bond is an important process in the formation of volatile products. This information has led to the postulation of a possible mechanism for the thermal degradation of the elastomer. Quantitative kinetic measurements were made by evaluating the overall rate of production of volatile products using the TIC obtained from sequence pyrolysis experiments. The data leading to this overall rate constant ( k) was interpreted in several ways, i.e. according to the Ericsson, Guggenheim and Kezdy-Jaz-Bruylants methods. The average values obtained for this overall rate constant were 0.16±0.03, 0.25±0.03, and 0.55±0.20 s −1 for pyrolysis temperatures of 350, 387, and 400 °C, respectively.