456 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS At higher temperatures, therefore, other reactions affect a higher proportion of the molecules, and the effects are lost. MR. A. FOSTER: I notice you do not mention trying triethanolamine as a possible reactant. Can you comment? TI•. L•.CT•JR•.R: It does not react. It is necessary to have sufficiently widely spaced reactive groups-and the hydroxyl groups in triethanolamine would not be sufficiently far apart. Even the butane diol for some reason interferes with the reaction rather than reacting itself, which is quite an interesting point. It is mentioned that we did try diamines where the two amino groups were closer together than in the 1:6, and we found that the 1:4 diamine reacted as opposed to the interference by the 1:4 diol. The 1:3 diamine also reacts in this way but in spite of claims in a patent (4) we can not make ethylene diamine work. The original patent (4) referred to the forma- tion of an insoluble product by reaction of propylene glycol alginate and ethylene diamine present together in a film, and it is very difficult to say whether, in these conditions, the amine is reacting or whether it is simply an effect of the alkali on the propylene glycol alginate. DR. F. J. WEYMO•J•I•: You have given us some information concerning the effect of propylene glycol alginate on starches and polyvinyl alcohol. Have you any- thing to say about the effects with cellulose ethers? TI•. L•c•uR•R: It does give a gelling effect with carboxymethyl cellulose, and also with other cellulose ethers but not very strongly. We have not looked at them very thoroughly and we paid more attention to substances that showed greater effects, in particular starch and polyvinyl alcohol. MR. C. PuGI•: It seems to me that the fact that it is necessary to have a fairly high minimum concentration before you change from hydrolysis to cross-linking must have some influence on the theory involved. Would you care to comment any more on this aspect? TI•. L•.c•uR•-R: I think the hydrolysis reaction is probably going on at the same rate all the time and you get the effect of increase of viscosity only if conditions are suitable for the cross-linking reaction to take place faster than the hydrolysis. If we have some reaction in which, say, a hydroxyl group in the propylene glycol alginate goes to one of the ester groups, it is fairly reasonable to suppose that as the concentra- tion is increased the probability of this reaction increases quite steeply. MR. J. J. H¾•)•.-SMITI•: You say in page 455 that the PGA-starch product is broken down by enzymes. Would you like to comment on this, compared with the normal stabilising of starch solutions against enzymic breakdown by PGA? TI• L•.CTUR•R: This stabilising action is effective only over the pH range of 3-4.5, a range in which amylyric enzymes do not normally function. I see you do not quite agree with that and perhaps I should say that it is a less important range in digestive processes. We have checked the claims of the patent (8) and agree that inhibition takes place in the stated range, but not appreciably at high pH values. Digestion of starch normally starts with the action of amylase in the saliva, and at the pH to be expected in the mouth there is no inhibiting effect from PGA. On the question of enzymic breakdoxvn, it is rather interesting that the gelatine- (8) U.S. Pat. 3 332 786: Method of preparing enzyme stable starch and product.

NEW REACTIONS OF PROPYLENE GLYCOL ALGINATE 457 propylene glycol alginate complex does not seem to be broken down in the stomach. (Simply from looking at in vitro experiments, using commercial pepsin in stomach conditions.) It is, however, broken down by pancreatin so there is the possibility that it could be used in a capsule which has to pass through the stomach and be effective lower down. Me. M. G. DE NAVARRE: Since the alginate which you are describing is made by a reaction between propylene oxide and the alginic acid, do you not get some ether formations between propylene oxide and the hydroxyl groups? Could not these, in fact, be somewhat responsible for the erratic results that you seem to be getting under certain conditions, as you are referring here to hydrolysis? THE LEc•ruRI•R: It is possible. Very little is known about that as it is rather difficult to demonstrate it analytically. Nobody has been able to show the presence of ether groups, although they may be there. However, the conditions for reacting alginic acid with propylene oxide are generally not those conducive to ether formation. On the question of the reaction, we did speculate at one time that possibly propylene oxide could be an intermediary but we tested that by putting propylene oxide in the mixture in alkaline conditions and we did not get any effect at all, either way.