Der abbau von polyoxymethylenen. Poloxymethylene. 14. Mitteilung

Abstract

ZUSAMMENFASSUNG:Quantitative Untersuchungen uber die Zersetzung von Polyoxymethylenen unter verschiedenen Bedingungen eeigen, daB im wesentlichen 5 Abbaureaktionen unterschieden werden konnen 1. Depolymerisation vom Kettenende her, 2. .4utoxydative Spaltung, 3. Abbau durch Sekundarprodukte der Autoxydation, 4. Thermische Degradation, 5 . Hydrolyse und Acidolyse. Die einzelnen Reaktionen lassen sich experimentell getrennt untersuchen. Es werden Moglichkeiten angegeben, den Abbau zu unterdriicken. Eine Methode zur Priifung der thermischen Stabilitat von Polyoxymethylenen wird vorgeschlagen. SUMMARY: under different conditions. that essentially five reactions take place :It is shown by quantitative measurements of the degradation of polyoxymethylenes 1 ) Depolymerization, starting on both ends of the polymer chain; 2) Autoxydative fission; 3) Decomposition by secondary products of autoxydation: 4) lherrnal degradation; 5) Hydrolysis and acidolysis.

Thermooxidation rate of diacetate terminated polyoxymethylene with various morphological structures

“…In accordance with the mechanism adopted here the chain ends are not involved in the degradation process. This suggestion was supported by the observation [1,16] that no change should occur in the intensity of the carbonyl bands at 1750 cm -1 due to ester end groups. The authors of [1] and [16] observed an increase in C = O/~/~/absorption which constitutes additional ) H evidence of the formation of fairly long, relatively stable chains.…”

“…This suggestion was supported by the observation [1,16] that no change should occur in the intensity of the carbonyl bands at 1750 cm -1 due to ester end groups. The authors of [1] and [16] observed an increase in C = O/~/~/absorption which constitutes additional ) H evidence of the formation of fairly long, relatively stable chains. They also observed additional changes in the 1275-1300 cm -1 region, which can be connected with the chain scission.…”

Review on the thermo-oxidative degradation of polymers during processing and in service

“…The long term heat degradation of polyacetals is a combined process of oxidation and acidolysis [144][145][146][147]. In first instance polyacetals oxidizes according to the mechanism shown in Scheme 1, with the oxidation taking place at the methylene groups.…”

Polyoxymethylenes

“…Formic acid, which can initiate an acidolytic chain scission, is formed as byproduct of the decomposition by oxidation of formaldehyde or by disproportionation. Acidic catalyst residues can also produce chain scission [98,99]; for further details, see [100].…”