GB1044863A - Stabilized polyoxymethylenes - Google Patents

Abstract

A resinous composition comprises a base-stable high molecular weight polyoxymethylene having dispersed therein 0.01 to 5% of a compound <FORM:1044863/C3/1> where R is hydrogen, an alkyl group of 1 to 20 carbon atoms, an alicyclic group of 3 to 8 carbon atoms, an aryl group of 6 to 10 carbon atoms, an aralkyl group of 7 to 30 carbon atoms, or a carboxyalkyl group of 2 to 10 carbon atoms and R1, R2 and R3 are one of the foregoing groups or amino groups. In the examples pyrazole, 3,5-dimethylpyrazole, 3-aminopyrazole, 3-amino-4-carbethoxypyrazole, 1-phenylpyrazole, 3-methylpyrazole and 3,5-dimethyl-1-phenylpyrazole are the stabilizers used. Others are specified. The pyrazoles are incorporated by dry blending followed by melt processing, a thermal stabilizer, e.g. a polyamide and an antioxidant, e.g. 2,21-methylene-bis - (4 - methyl - 6 - tert. - butylphenol) also being added. The polyoxymethylene may be prepared by polymerizing formaldehyde and thereafter converting the polymer to a base-stable polyoxymethylene ether. Alternatively, a base-stable copolymer composed of oxymethylene units interspersed with substituted alkylene or oxyalkylene units is employed. In both cases unreacted polyoxymethylene is removed by dissolving the product in a solvent and heating it, optionally in the presence of a strong amine or caustic, to depolymerize the unreacted polyoxymethylene, or alternatively by heating the solid or molten polymer.