Procédé pour la préparation de dérivés vinyliques

Condensation products soluble in appropriate solvents to give a solution of relatively high viscosity are manufactured by condensing a polyvinyl alcohol with formaldehyde or a polymer thereof in the presence of an acid or acid reacting catalyst, the amount of catalyst being chosen by determining experimentally the maximum quantity which gives a product insoluble in the solvent selected and then using an amount slightly in excess of this quantity. The excess should in general not exceed 10 per cent of the experimentally determined quantity when working at room temperature, and should usually not exceed 1 per cent of the total reaction mass when using hydrochloric acid. In examples: (1) a polyvinyl alcohol having a viscosity of 38 seconds Engler as a 4 per cent aqueous solution at 15 DEG C., is condensed with trioxymethylene in aqueous solution at 20 DEG C. in the presence of 7 per cent (on the total mass) of hydrochloric acid, to yield a product soluble in a mixture of methylene chloride and alcohol (6,7 per cent of acid being the maximum quantity giving an insoluble product); (2) a polyvinyl alcohol of 68 seconds Engler viscosity is used and the condensation is effected in the presence of 25 per cent of sulphuric acid (23,5 per cent being the maximum quantity giving an insoluble product). Specifications 337,806, [Class 2 (iii)], and 351,082* are referred to.