Patent GB-645405-A (GB)
Title: Improvements in or relating to polyvinyl acetate and to a polymerisation catalyst for use in its production
IPC: F02P7/06
Filed: 1947-05-20
Abstract: Chewing gum grade polyvinyl acetate of viscosity within the range from 1.6 down to 1.2 centipoises is obtained by bringing together vinyl acetate containing not more than 0.05 per cent by weight of acetaldehyde, toluene as diluent in an amount at least as large as the weight of vinyl acetate and a solution containing 9 to 33 per cent by weight of acetyl peroxide in a solvent consisting of toluene or vinyl acetate, causing polymerization to take place and recovering the polymer from the reaction mixture. The acetyl peroxide solution is prepared by reacting acetic anhydride with a per-oxygen compound in the presence of toluene or vinyl acetate (see Group IV (o)).  The concentration of catalyst as acetyl peroxide based on the weight of the monomer is preferably from 1.5 to 6.6 per cent.  The polymerization may be carried out as a batch operation or continuously.  In examples: a mixture of vinyl acetate, toluene and of the acetyl peroxide catalyst prepared by using toluene as solvent (see Group IV (b)) is heated under reflux for 3 1/2 hours and then steam distilled.  The residue consisting of polyvinyl acetate is then vacuum dried at a maximum temperature of 150 DEG  C.  Specification 387,323 and U.S.A. Specification 2,085,490 are referred to.ALSO:A vinyl acetate polymerization catalyst containing acetyl peroxide as the active constituent is prepared by reacting acetic anhydride with a per-oxygen compound in the presence of a solvent consisting of toluene or vinyl acetate, to form a solution containing acetyl peroxide, the reaction temperature when vinyl acetate is used as solvent being maintained below that at which appreciable polymerization of the vinyl acetate would occur and washing the resulting solution with successive portions of water until the acidity of said solution is below 1 per cent, and preferably below 0.5 per cent, calculated as acetic acid. Specified per-oxygen compounds are sodium perborate and hydrogen peroxide of 27 1/2 per cent or higher strength.  In examples (1) a stirred mixture of toluene, acetic anhydride and calcium hydroxide is maintained at 20-25 DEG  C., and 27 1/2 per cent hydrogen peroxide added in portions.  The aqueous layer is then separated and the hydrocarbon layer washed with three successive portions of water to give an acidity of 0.1 per cent as acetic acid; the preferred molar ratio of anhydride to hydrogen peroxide is 2 : 1; (2) 27 1/2 per cent hydrogen peroxide is slowly added to a mixture of vinyl acetate, acetic anhydride and calcium hydroxide cooled to 5 DEG  C., the temperature being maintained at 10 DEG  C. during the addition of the peroxide. The vinyl acetate layer is then washed with three or four portions of ice water to reduce the acidity to below 0.05 per cent as acetic acid; (3) acetic anhydride is added to a cooled mixture of toluene and sodium perborate while maintaining the temperature between 25 DEG and 30 DEG  C.  The charge is then washed with three portions of water at about 35 DEG  C. to reduce the acidity to 0.1 per cent as acetic acid.  The catalyst is preferably prepared so as to contain 9 to 33 per cent of acetyl peroxide by weight and in this concentration may be used to prepare chewing gum grade polyvinyl acetate from vinyl acetate (see Group IV (a)).  Specification 387,323 is referred to.ALSO:Polyvinyl acetate of chewing gum grade free from taste and odour and having a low viscosity of from 1.6 down to 1.2 centipoises is obtained by polymerizing vinyl acetate in the presence of toluene as dilutent and using a catalyst consisting of a solution of acetyl peroxide in toluene or vinyl acetate, (see Group IV (a)).  The acetyl peroxide catalyst is prepared by reacting acetic anhydride with a per-oxygen compound in the presence of toluene or vinyl acetate, (see Group IV (b)).  The polyvinyl acetate is stated to form a complete or partial substitute for gum chicle or other masticable resins used in chewing gum compositions and may readily be incorporated with plasticisers, softeners, fillers, sugar and flavouring matter or other known ingredients.