PROCESS FOR PRODUCING HIGH MOLECULAR WEIGHT POLYMER OF FORMALDEHYDE

A high molecular weight polymer of formaldehyde is prepared by polymerizing formaldehyde in a solution or dispersion containing carbon dioxide. The carbon dioxide may be the sole solvent or dispersion medium or there may also be present an organic solvent of boiling point up to 40 DEG C., e.g. ethane, butane, propane, t.-pentane, dimethyl ether, diethyl ether and their mixtures. The polymerization may take place in the presence or absence of a catalyst which may be anionic or cationic triethylaluminium, tri- - n - butylamine, triphenylphosphine, calcium stearate trimethylamine, tin tetrachloride and boron trifluoride being amongst those listed. Alternatively the polymerization may be promoted by irradiating the reactants with X-ray or ionizing radiation at - 78 DEG to +20 DEG C. An acylated polymer may be prepared by polymerizing the formaldehyde in carbon dioxide solvent in the presence of a carboxylic acid anhydride and after polymerization heating the whole reaction system, or the residue after returning the reaction system to atmospheric pressure and recovering carbon dioxide and unreacted formaldehyde, to above 100 DEG C. to complete the acylation. The carboxylic acid may be present in an amount up to 50 mol per cent of the formaldehyde acetic, propionic, benzoic, stearic and caproic anhydrides, being specified as well as those of polybasic acids. The formaldehyde starting material may be prepared by concentrating a neutral aqueous solution of formaldehyde or there may be used a mixture of formaldehyde and carbon dioxide obtained by liquefying the gaseous product from thermally decomposing a low-molecular weight formaldehyde polymer in a stream of carbon dioxide.