Societa' Italiana Resine S.i.r. S.p.a.

Sergio Custro

Pierino Radici

Paolo Colombo

Mario Ermoni

The terminal hydroxyl groups of an acetal polymer are esterified or etherified by reaction with an end-capping agent chosen from anhydrides of carboxylic acids, orthoesters and orthocarbonates, by forming an intimate mixture of polymer in powder form and liquid end-capping agent, the amount of said agent in the mixture being less than that which results in loss of the free-flowing characteristics of the powder, and reacting said mixture under stirring at 50.degree.-170.degree. C.

Process for improving the stability of acetal polymers

The thermal and chemical stability of etherified acetal homopolymers is improved by heat-treating the latter in the molten state at a temperature of at least 180.degree. C., in the presence of a halide of an alkali or alkaline earth metal, until substantially complete degradation of the unstable polyoxymethylene chains.

Process for improving the stability of etherified acetal homopolymers

An etherified acetal homopolymer is stabilized by heat-treating said homopolymer suspended in a liquid diluent chosen from water or mixtures thereof with polar organic compounds, preferably in the presence of a basic compound, at a temperature of 100.degree.-160.degree. C and below the melting point of the homopolymer, thereby to substantially degrade the unstable fraction of said homopolymer.

The unstable terminal hydroxyl groups of acetal polymers are etherified in a liquid reaction medium in the presence of organic additives.

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Gorla Maggiore, Italy

Sergio Custro