POLYVINYLPYRROLIDONE IN COSMETICS 203 containing 1 per cent w/v of total solids using a suitable viscometer. K value is then calculated in accordance with the following equation. K value = 1000 k, •vhere 75k • Log nrel= 1 + 1.51• + k The Fig. 7. The water de-ionisation unit used to provide water for carrying out the polymerisation of v/nyl pyrrolidone monomer. For most purposes a polymer having a K value bet veen 30 and '35 appears to be most useful. The complex-forming ability of polyvinyl- pyrrolidone does not appear to be much affected by the molecular Weight, and for film-forming uses, this medium molecular weight material gives solutions of reasonable viscosity. High molecular weight materials, as one

204 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Fig. $. The co•ro! room of the •cetyle•e high-pressure building. would expect, give solutions of extremely high viscosity, and these may find application as special-purpose thickening agents, etc., but they are otherwise of relatively little commercial interest in this country at the present time. 4. COSMETIC AND TOILET PREPARATION USES OF POLYVINYLPYRROLIDONE (a) General Apart from the general properties of polyvinylpyrrolidone reviewed above, the cosmetic chemist will be interested to know that it is a stable substance, uniform in its properties and, as far as we know, without harmful physiological effects, although clearly in any new application it is essential to check this by the usual methods. The study of the possible uses of polyvinylpyrrolidone in cosmetics and toilet preparations appears to have originated from work carried out in America by Shelanski, Shelanski and Cantor, ø who demonstrated that polyvinylpyrrolidone is substantive to human skin and hair. The resultant films leave the skin smooth and soft to the touch, and when the polymer, suitably formulated, is applied to the hair it imparts a conditioning effect, enhancing its appearance and manageability.