POLYMER EVOLUTION--FROM NATURAL TO SYNTHETIC 29 SYNTHETIC POLYMERS Methyl vinyl ether maleic anhydride copolymers The use of a natural polymer as the backbone for a semi-synthetic polymer does, however, have some limitations. In the fibre, the cellulose chains are more closely compacted in some places than in others, with the result that etherification is not completely uniform and the solutions are to some extent heterogeneous. Where complete homogeneity is essential, it is better to adopt a wholly synthetic process. The basic methyl vinyl ether maleic anhydride resins {MVE/MA) are alternating copolymers manufactured by polymerisation of methyl vinyl ether with maleic anhydride in presence of a peroxide catalyst and a hydrocarbon solvent. The polymeric anhydrides are filtered off from the hydrocarbon solvent and after drying are in the form of a very fine white powder. The resins consist of repeating units of the following structure: CH 3 o -C--C-C--C- a2a I C C //\ 1\\ 0 0 0 The number of repeating units can be varied to give a range of vis- cosities, and a third monomer can be introduced to confer specific properties. Very high viscosities can be obtained by the use of crosslinking agents during polymerisation. MVE/MA hydrolyses in water giving clear solutions of the free acid. This reaction takes place over about 48 h at room temperature but can be reduced to 20 min by heating at 00øC (Fig. 1). The anhydride is also soluble in the more polar organic solvents such as ketones, aldehydes, esters and alcohols.

3O JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 300 250 .c_ 2OO •5o IOO 50 50 75 I00 Temperature• eC Figure I Variation in solution time of MVE/MA copolymer with temperature In the case of alcohols, solution is accompanied by half ester formation. CH3 I o I -C-C•-C-C- •2• I I c c // \ / \\ o o o q- ROH---• CH 3 I o I --C--C-C-C- H2H J J C C 0 0 0 0 R H