POLYVINYLPYRROLIDONE IN COSMETICS 201 EFFECT OF DILUENTS ON POLYVINYLPYRROLIDONE SOLUBILITY MI. of Diluent added to Procure a Cloudy Mixture with 20 mi. of P.V.P. Solution Solvents -- Benzene Xylene White Ether AR Ethyl Spirit Acetate Chloroform (AR.) ß. 23 11 7 16 -- I.M.S ..... 32 15 6 26 -- Cellosolve .. 100 100 20 46 200 .. Nitrobenzene .. 18 5 4 unsuitable 22 Methancl (Tech.) .. 100 49 unsuitable 52 2 100 Based on 10 per cent solution of P.V.P. Fig. 12. Solubility of polyvinylpyrrolidone in organic solvents. Fig. 5, General view of the purification section with a vacuum receiver shown in the foreground. in powerful solvents will tolerate considerable dilution with hydrocarbons this is useful in certain applications. Apart from its unique solubility p, operties, the polymer has the novel property of forming complexes with many substances very varied in chemical structure•for example, dyestuffs, iodine, antibiotics, insulin, etc.--and many industrial and pharmaecutical applications have been developed which take advantage of this property.

202 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Apart from this, polyvinylpyrrolidone behaves in many ways in a manner typical of the natural proteins such as albumin, and is capable of tanning by prolonged heating or by tieatment with tanning agents---for example, resorcinol, tannic acid, etc. It is also possible to form stable gels of the polymer by treatment with persulphates.• • In manufacturing the polymer it is possible, by the suitable adjustment and choice of catalysts, to prepare materials with K values ranging from about 20 to about 100, the corresponding mean molecular weights lying somewhere between 10,000 and 700,000. The K value of the polymer is, of course, a function defining the mean molecular weight of the material, and is determined by measuring the relative viscosity of an aqueous solution Fig. 6. A general view of the vinyl pyrrolidone polymerisation plant.