Patent GB-387353-A (GB)
Title: Process of controlling molecular aggregation in the polymerization of vinyl esters
IPC: C08F18/04
Filed: 1931-04-30
Abstract: In the polymerization of vinyl esters by heat in the presence of a diluent and a polymerization catalyst, the polymerization is controlled by carrying it out in the presence of an amount of diluent calculated to give, at the temperature employed, the desired softening point and viscosity, the ratio of the amounts of diluent and unpolymerized ester in the reaction mixture being maintained substantially constant.  Preferably the temperature is maintained substantially constant during the polymerization.  As catalyst may be advantageously employed the product of reaction between an aliphatic acid anhydride and hydrogen peroxide, sodium peroxide or a true per-salt.  The constant ratio of the amounts of diluent and unpolymerized ester may be maintained by withdrawing the diluent in amount increasing as the amount of unpolymerized ester decreases. This may be effected by carrying out the reaction under a reflux condenser so that a portion only of the condensate is returned and a mixture richer in ester than that refluxed is fed into the reaction vessel, or by carrying out the reaction under a fractionating column so that all or substantially all the ester is returned but only sufficient diluent as is necessary to maintain the constant ratio. Tables are given showing the effect on the viscosity of the product of various amounts of toluene in the polymerization, at approximately 100 DEG  C. with the aid of benzoyl peroxide, of (a) vinyl acetate freed from acetaldehyde, and (b) commercial vinyl acetate containing ,05 per cent of acetaldehyde.  Other organic liquids, e.g. an alcohol or benzene, may be employed as diluents, the choice and proportion of diluent depending on the nature of the product desired.  In examples: (1) vinyl acetate freed from acetaldehyde is refluxed with the product obtained by reacting sodium perborate and acetic anhydride in toluene and separating the toluene solution of the catalyst from the insoluble residue.  When refluxing starts the vapours are passed into the middle of a refluxing column, whereby the vinyl acetate is vaporized, removed through a condenser above the column and returned to the reaction mixture whilst the correct amount of toluene is returned from the base of the column.  (2) A mixture of vinyl acetate, toluene and the catalyst of (1) is heated in a kettle under a reflux condenser and the product steam distilled.  (3) A mixture as in (2) is run at a constant rate into the kettle containing the undistilled product of (2), provision being made for constant level overflow. The constant feed and draw off are continued until the viscosity of the products drops to a constant value and are then maintained while heating sufficiently to give a moderately slow refluxing. (4) Vinyl acetate free from acetaldehyde is mixed with butyl acetate and a catalyst produced by reacting sodium perborate and acetic anhydride in butyl acetate and separating the solution from the insoluble residue.  Part of the mixture is refluxed with agitation in a vessel with a side tube through which the material can be withdrawn, and the remainder is run in while polymerized vinyl acetate is withdrawn at the same rate.  Similar results are obtained by replacing butyl acetate by ethyl or butyl alcohol or ethyl acetate.  A somewhat higher degree of polymerization is obtained by replacing toluene by an equal amount of butyl acetate-butyl alcohol mixture.  Other vinyl esters specified are vinyl formate, butyrate and propionate.  Specifications 15271/14, [Class 2 (iii), Dyes &c.], and 387,323 are referred to.  The Specification as open to inspection under Sect. 91 comprises also the polymerization of vinyl esters in the presence of at least two substances which influence the degree of molecular aggregation to different extents.  In a preferred method of working, one of the substances, e.g. an aldehyde, is very active and is used in amount less than is necessary to obtain the desired degree of polymerization, and the other substance, e.g. a diluent such as toluene, benzene or an alcohol, is much less active and is used in amount necessary to supplement the action of the active substance to the extent that the desired degree of polymerization results.  The control of the polymerization by means of a saturated aliphatic aldehyde alone is also described.  The polymerization may be effected in any known manner e.g. by heat or heat and pressure, in the presence or absence of catalysts, by bombing or by refluxing, or by the action of radiation, e.g. from a mercury vapour lamp.  Additional examples describe the polymerization of vinyl acetate free from acetaldehyde by refluxing with various amounts of toluene using the catalyst of Example (1) of the Specification as accepted, and of vinyl acetate containing ,05 per cent of acetaldehyde by heating in an aluminium autoclave with toluene and benzoyl peroxide. Specifications 280,246 and 295,322, [both in Class 2 (iii), Dyes &c.], are referred to.  This subject-matter does not appear in the Specification as accepted.