PROCESS FOR PREPARING HIGH MOLECULAR WEIGHT POLYMERS OF FORMALDEHYDE

Formaldehyde polymers crystallizable in orthorhombic form are prepared by contacting a polyoxymethylene (e.g. paraformaldehyde) in an aqueous medium with an excess of a metastable aqueous formaldehyde solution in the presence of an alkali metal or quaternary ammonium salt of carboxylic acid at a pH higher than 6 and at 20 DEG to 60 DEG C. The polymerization may be carried out in a stationary state at 35 DEG C. or continuously be feeding the reactor with a concentrated aqueous solution of formaldehyde, sodium formate and sodium hydroxide and discharging continuously the polymer and a dilute aqueous formaldehyde solution, this solution may be enriched with formaldehyde by direct absorption of the vapours from formaldehyde synthesis and returned to the polymerization process. The continuous process may take place in two stages, a rapid first stage leading to low molecular weight polymers which are recovered and a second slower stage to increase the molecular weight. The products may be acetylated.