Catalyst for high mol. wt. polyoxymethylene prepn. - comprises ammonium lactamate esp. pyrrolidonate, piperidonate, lauryl-lactamate or capro:lactamate

A catalyst for preparing polyformaldehyde comprises an ammonium salt of formula (I) A-N+R2R2R3R3 (I) (where R1-4 are (cyclo)alkyl or (alkyl)aryl and A is a lactamate residue of formula (II) and B is a 3-13C linear polymethylene chain in which one or more of the H atoms may be opt. substd. by (cyclo)alkyl or (alkyl)aryl). (I) has high activity with a practically quantitative yield in polyformaldehyde. The polymers have narrow mol.wt. distribution, high mol.wt. and high bulk density so that they can be easily removed from the reaction medium by decantation or filtration. The filtered polymer has a low content of diluent. The catalyst residues do not have to be removed; they degrade during stabilisation of the polyoxymethylene and gps. e.g. esterification or etherification. Polymerisation can be carried out continuously.