AbstractCationic polymerization of monomeric formaldehyde has been studied at low temperature. It was found that high molecular weight polyoxymethylene with the reduced viscosity higher than 1.0 dl/g was readily obtained when the polymerization of formaldehyde was carried out in saturated hydrocarbons in the presence of LEWIS acids, BRÖNSTED acids, I2, ICl ICl3, IBr, sulfur dioxide and binary systems of sulfur dioxide with these compounds at considerably low temperature. The degree of polymerization was effected by the polymerization conditions, especially solvent, polymerization temperature and addition of chain transfer agents such as water, formic acid, methanol or methyl formate.