Non-oxidative thermal degradation of poly(ethylene oxide): kinetic and thermoanalytical study

Study of the thermal decomposition of well-characterised poly(ethylene oxide) (PEO) under non-oxidative conditions has been conducted by thermogravimetry (TG) in both dynamic and isothermal mode and by thermogravimetry coupled on-line with infrared spectroscopy (TG/FTIR) or mass spectrometry (TG/MS). Kinetic analysis, based on isoconversional methods, yielded value of (apparent) activation energy at the level of 145-180 kJ/mol. Further evaluation of the kinetic model function f(α) by non-regression analysis revealed that phase boundary-controlled reaction is a rate-determining kinetic approach which can have the character either of a surface chemical reaction or of diffusion. Analysis of the evolution of low-molecular weight decomposition products by TG/FTIR and TG/MS techniques showed that main decomposition products are ethyl alcohol, methyl alcohol, alkenes, non-cyclic ethers (ethoxymethane, ethoxyetane and methoxymethane), formaldehyde, acetic aldehyde, ethylene oxide, water, CO and CO2. Condensed phase FTIR spectra do not show formation of any stable functional groups or structures which is an additional confirmation of the kinetic data that indicate on the dominating role of phase boundary-controlled reactions during the thermal decomposition; volatile low-molecular weight decomposition products that are formed on the surface with the reaction rate proportional to the surface area/diffusion coefficient undergo eventually a rapid vaporization at the temperature higher than 300 °C.