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Thermal degradation processes are of great importance in the case of polyoxymethylene. Establishment of the mechanism of oxidative decomposition is particularly important, because it proceeds under conditions when depolymerization is predominant over oxidation. The basic kinetic regularities of thermal and thermal‐oxidative degradation of polyoxymethylenes have been determined, and differences have been observed; that depend on the chemical nature of endgroups. Thermal degradation proceeds as depolymerization with generation of active centers at the chain end for POM hydrate, and following the “random law” for end‐capped POM and copolymers. The “kinetic” chain is shorter than the “substance” one. Formaldehyde participates in chain transfer of POM degradation. A method has been proposed for determining the true activation energy of reactions that are more complicated due to heat transfer. The true E of POM for different end groups has been determined. The thermooxidative decomposition proceeds as depolymerization initiated by oxygen and follows the “random law.” Oxygen has an inhibiting effect by reacting with active centers of POM. The degradation rates and accumulation of formic acid depend on the nature of end groups, and HCOOH acts as an accelerator. The most probable sources of HCOOH were proposed, and the active centers of POM degradation are shown to be of a dual nature. The mechanism of degradation and some principles of stabilization are proposed.

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synopsisThe kinetics and parameters of thermal and acidic degradation of poly-1,s-dioxolane were investigated in order to elucidate the mechanism of degradation and to obtain information on the nature of active centers. Both homolytic and heterolytic breaking of a macromolecule were shown to be random and occur a t the acetal bond. Thermal degradation was found to proceed in two stages, depending on temperature and involving active centers of a different nature, i.e., macroions and macroradicals. The rate-determining step of thermal degradation appears to be one involving the radical component, similarly to thermal degradation of olefin polyoxides. Acidic degradation occurs solely by the depolymerization mechanism, as in the case of polyaldehydes. It was concluded that the degradation mechanism depends not only on the chain structure and the thermodynamic properties of the system, but also on the nature of active centers.

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