SU434089A1 - - Google Patents

Description

(54) METHOD OF OBTAINING PRIVATED COPOLYMERS

one

The invention concerns a process for the preparation of graft copolymers with any content of graft monomers in an aqueous suspension by grafting monomeric unsaturated polymerizable compounds to polymers.

A known method of producing graft copolymers in an aqueous suspension, consisting in dissolving the polymer in the graftable monomer, the resulting solution is suspended in water with the addition of suspension stabilizers and in the presence of polymerization initiators dissolved in the monomers, is grafted at elevated temperature. The resulting heat of polymerization must be removed by cooling, which requires additional equipment. The introduction of the organic phase into the aqueous phase is carried out at room temperature or at moderate temperature.

The disadvantage of this method is the insolubility or limited solubility of polymers in some graftable monomers. The solubility of the polymer in the monomer can be improved by the addition of suitable organic solvents, but in this way, due to the chain-breaking action of the solvents, the yields of graft copolymers and products with a lower molecular weight and poorer qualities are lower than in the absence of solvents. In addition, the removal of the solvent from the graft copolymer creates great difficulties and is an additional operation. The addition of organic solvents can be avoided by subjecting the polymer to swelling in the monomer, then it is dispersed in the aqueous phase and copolymerized by grafting.

in the presence of radical initiators. However, the dispersion of the swollen polymer in the aqueous phase creates considerable difficulties, and the resulting products are relatively non-homogeneous.

To carry out copolymerization by grafting in the presence of solvents while improving the heat of polymerization, a method has been proposed, but a solution of the polymer, the monomeric unsaturated polymerizing compound and the polymerization initiator in an organic solvent, whose vapor pressure is higher than the vapor pressure of the subsequent aqueous phase, is introduced with vigorous stirring into the aqueous phase, which, if necessary, contains a suspension stabilizer, and the temperature of the aqueous phase is higher than the boiling point -ethnic solvent. The organic solvent, evaporated upon entry into the aqueous phase, is immediately removed from the reaction mixture. The copolymerization is added with heating and vigorous stirring. The graft copolymer falling out in the fine-grained state is separated in the usual way.

The method can be carried out as follows.

An aqueous phase consisting of water or a water-glycerol mixture and a suspension stabilizer are placed in a reaction vessel equipped with a stirrer. Then, with vigorous stirring, a cold solution consisting of a polymer, a monomer compound, a polymerization initiator and an organic solvent (whose vapor pressure is higher than that of the aqueous phase) is metered into the aqueous phase heated to a temperature above the boiling point of the solvent. The solvent that evaporates upon entry into the aqueous phase is immediately removed from the reaction mixture by distillation, which better removes the heat of reaction without additional cooling, and also prevents the presence of a solvent during the graft polymerization. In a finely dispersed mixture of polymer, monomers and initiator, the graft copolymerization immediately begins and finely dispersed or pearl-like suspension copolymers are formed which do not contain a solvent and can be easily separated from the aqueous phase by filtration or centrifugation.

The distilled solvent, containing, on occasion, small amounts of monomers and water, can be used again in both the continuous and batch processes.

All organic compounds can be used as solvents, the vapor pressure of which is higher than that of the aqueous phase used and in which the graftable monomer dissolves at any ratio. Depending on the polymer and the aqueous phase, benzene, other aromatic hydrocarbons, carbon tetrachloride, other chlorinated hydrocarbons or lower alcohols are preferably used as solvent. The amount of solvent added depends on the solubility of the polymer used in the monomer or in a mixture of monomers. And the monomer itself can replace the solvent, if its vapor pressure is higher than the vapor pressure of the aqueous phase.

The volume ratio of the aqueous and organic phases is from 1: 1 to 5: 1.

The organic phase should preferably be at room temperature before it is added to the aqueous phase.

As monomeric unsaturated polymerizable compounds, all unsaturated compounds can be used, which dissolve in the organic solvent used, regardless of whether it can be dissolved in any ratio, and also the polymer in the monomer used, for example, vinyl chloride, binine acetate, acrylonitrile, styrene, chloride vinylidene or mixtures of such compounds.

All polymers and copolymers soluble in the mixture of solvents and monomers used, for example polyethylene, copolymers of ethylene and

vinyl acetate, polyvinyl chloride or polyvinyl acetate.

To disperse the organic phase, 0.1-3 wt.% Is added to the aqueous phase. % (in terms of water), the usual suspension stabilizers, such as polyvinyl alcohol or methylcellulose.

The initiation of graft copolymerization is carried out using conventional organic peroxide and azo compounds which dissolve in the monomers and decompose at the reaction temperature. They are added in amounts of from 0.01 to 3 wt. % of the amount of polymer and grafted monomers. Polymerization can be carried out in the temperature range.

from 20 to 150 ° C both at elevated pressure, and in vacuum or at normal pressure.

The properties of the products depend largely on their composition. According to the proposed

The process can be used to obtain graft copolymers with any graft monomer content, even if the polymer only partially dissolves in the monomer. In addition, this method can be used to inoculate monomers, in which the polymer does not dissolve, using suspension polymerization.

Example 1. 80 g of ethylene-vinyl acetate copolymer are completely dissolved in 250 ml

benzene by heating, and after cooling, 20 g of styrene and 3 g of p, p-azodiisobutyrodinitrile are added. This mixture is fed dropwise into a solution of 20 g of saponified polyvinyl acetate in 400 g of distilled water, heated to

80 ° C, with vigorous stirring and simultaneous distillation of benzene. The reaction time is 4 hours. The graft copolymer is obtained in the form of a fine-grained suspension polymer, which can be easily separated from the aqueous

phases.

To remove the homopolymer, the resulting product is evaporated with acetone and washed. The analytical data, determined after drying, are compared with the data of the initial copolymer in Table. one.

Example 2. To cold 300 g of a 10% solution of an ethylene-vinyl acetate copolymer in vinyl acetate, 2 g of dibenzoyl peroxide is added in the cold, and then it is added dropwise at

stirring 30 g of saponified polyvinyl acetate and 10 g of Metaupon paste solution (about 12% coarse impurity) in 800 g of distilled water heated to 80 ° C. The distilled vinyl acetate serves on the one hand to remove the heat of reaction, on the other hand to regulate the content of vinyl acetate in the graft copolymer. The graft copolymer is obtained in the form of a fine spherical and easily separated product within 4 hours. To remove the homopolymer, the product is evaporated with acetone, washed and dried. In tab. 2 its properties are compared with the properties of the original copolymer.

table 2

Example 3. The south of high-pressure polyethylene (Mirat 1300) is dissolved in 350 g of benzene at 80 ° C. After cooling, 10 g of vinyl acetate and 2 g of dibenzoyl peroxide are added. This solution is served cold.

state in droplets in the aqueous phase, heated to 80 ° C and consisting of 1000 g of distilled water, 50 g of Metaupon paste solution (12% coarse impurity) and 30 g of saponified polyvinyl acetate, with vigorous stirring and simultaneous distillation of benzene. After completion of the reaction (about 4 hours), the fine grained copolymer is separated from the aqueous phase, evaporated in order to remove the homopolymer with acetone, washed and dried.

In tab. 3 its properties are compared with the properties of the original polyethylene.

Table 3

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25

Subject invention

thirty

The method of obtaining graft copolymers by dispersing in the aqueous phase an organic phase consisting of a polymer solution, a monomer or a mixture of monomers and a polymerization initiator in an organic solvent with a vapor pressure higher than that of the aqueous phase, followed by polymerization with stirring w and is that, with the aim of improving the tehnologii

and the properties of the product, the organic phase is introduced into the aqueous phase, heated to a temperature above the boiling point of the organic solvent, and the evaporating solvent is immediately distilled from the reaction mixture.

mixes.