RU2265617C2 - Low-branched high-molecular polyvinyl acetate, method for its preparing and polyvinyl alcohol based on thereof - Google Patents

Abstract

FIELD: organic chemistry, polymers.

SUBSTANCE: invention relates to low-branched high-molecular polyvinyl acetate, methods for its preparing and to polyvinyl alcohol prepared on its base. Invention describes low-branched high-molecular polyvinyl acetate prepared by aqueous-emulsion polymerization of vinyl acetate in the presence of emulsifier and initiating agent wherein complexes of alkylcobalt (III) with tridentate ligands of the general formula (I)

are used as an initiating agent taken in the amount 0.04-0.2 mas. p., and the polymerization process is carried out at temperature 10-40°C. Polyvinyl acetate prepared by this method has molecular mass 850000 Da, not less, and degree of branching 0.39-0.7. Polyvinyl alcohol with the polymerization degree 6000 Da, not less, and the saponification degree 98-99.9% that is able for making high-module fibers is prepared by saponification of indicated low-branched polyvinyl acetate.

EFFECT: improved preparing method, valuable properties of product.

3 cl, 3 tbl, 10 ex

Description

The invention relates to a low-branched, high molecular weight polyvinyl acetate, a process for its preparation and polyvinyl alcohol, from which high-strength fibers made from this polyvinyl acetate are made.

One of the areas of application of polyvinyl acetate (PVA) is the production of high molecular weight polyvinyl alcohol from it, from which heavy-duty high-modulus fibers are made. For this purpose, as is known, PVA with a high molecular weight is required (patents US 5310790, US 5403905). Such a molecular weight is difficult to achieve due to the high value of the chain transfer constant. For example, in the reactions of chain transfer to monomer, the activity of vinyl acetate (VA) is 3-4 times higher than styrene, and when the chain is transferred to the polymer, it is 50 times. This leads to the formation of branched polyvinyl acetate, not suitable for the production of high molecular weight polyvinyl alcohol (PVA), intended for the manufacture of high modulus fibers (PVA).

PVA is obtained by radical polymerization of VA in bulk, solution, emulsion or suspension. However, the polymerization of VA in bulk and in solution is difficult to control, therefore, mainly PVA is obtained in emulsion or suspension.

A known method of producing high molecular weight PVA block or suspension polymerization of VA in the presence of a radical type initiator (AS USSR No. 507590, 1976). The process is carried out with the gradual introduction of monomer into the reaction zone during the process and alkanoyl-α-substituted alkanoyl oligoxide of the general formula [-C- (CH ₂ ) n-C-OO-C-CH- (CH ₂ ) _m - C-OO-] _k , where n = 4-12, m = 3-12, n + m> 9, k = 6-28, x = H, CH ₃ , C ₂ H ₅ , Br, Cl or I.

The disadvantage of this method is the technological difficulties associated with the synthesis, the high temperature of the process (72 ° C) (polymerization is carried out by boiling the reaction mixture). In addition, the resulting PVA has a high degree of branching (2.0–4.5), which adversely affects the physicochemical properties of the PVA obtained on its basis.

A known method of producing unbranched polyvinyl acetate (AS USSR No. 712823, 1980). The polymerization is carried out in bulk in the presence of triethylborane, the initiator is used in an amount of 0.019-0.296% by weight of the monomer. The disadvantage of this method is the low molecular weight of PVA (MM <540000), and the fact that the polymerization in the mass is difficult to control.

Closest to this invention in technical essence and the achieved result is a method for producing high molecular weight PVA by water-suspension polymerization in the presence of peroxide initiators and PVA obtained by this method (AS USSR No. 704946, 1979). As initiators, polymeric peroxides of dibasic aliphatic acids of the general formula are used here:

[-C- (CH ₂ ) _m -COO-] _n m = 5-16, n = 5-40

or tetracil peroxides of the general formula

RCOOC- (CH ₂ ) ₄ -COOCR, where R = CH ₃ , C ₂ H ₅ , C ₃ H ₇ , C ₆ H ₁₃ , C ₁₀ H ₂₁ .

The disadvantages of this method are the high process temperature (60-70 ° C) and high branching of the resulting PVA (γ = 2.4-3.4), which, as mentioned above, has a bad effect on the properties of the obtained PVA, namely, it does not allow it use for the manufacture of high modulus fibers.

The objective of the invention is to develop a method for producing a low-branched, high molecular weight polyvinyl acetate, as well as to obtain high molecular weight polyvinyl alcohol from it for the manufacture of high-modulus fibers.

The specified technical result is achieved by the fact that in the method for producing PVA by water-emulsion polymerization of vinyl acetate in the presence of an emulsifier and an initiator, the initiator is used

complexes of alkyl cobalt (III) with tridentate ligands of the general formula, where R = alkyl from C ₂ to C ₁₆ , in an amount of 0.04-0.2 parts by weight, and the polymerization process is carried out at a temperature of 10-40 ° C and pH 3 5-8.

The specified technical result is also achieved by the fact that the resulting low-branched, high molecular weight PVA has a molecular weight of at least 850,000 and a degree of branching of 0.39-0.7, which allows it to be used to produce PVA suitable for the manufacture of high-modulus fibers.

In addition, the technical result is achieved in that the saponification of PVA PVA is suitable for the manufacture of high modulus fibers and has a polymerization degree of at least 6000 and a saponification degree of 98-99.9%.

Comparative analysis with the prototype allows us to conclude that during the emulsion polymerization of vinyl acetate, a new type of initiator was used - alkyl cobalt (III) complexes with tridentate ligands. Thus, the claimed technical solution meets the criterion of "novelty."

An analysis of known technical solutions showed that the use of alkyl cobalt (III) complexes with tridentate ligands as initiators of emulsion polymerization of VA allows the process to be carried out in economically advantageous and technologically convenient conditions, at low temperatures and in one stage, without additives of components during the process. It also unexpectedly turned out that in the presence of alkyl cobalt (III) complexes with tridentate ligands, it is possible to obtain a low-branched, high molecular weight PVA. Thus, the claimed technical solution meets the criterion of "significant differences".

The indicated complexes are alkyl {2 - [(2-aminoethyl) imino] -pent-3-en-4-olate} (1,2-ethanediamine) cobalt (III) bromides (symbolic formula [RCo (acacen) (en)] Br) - synthesized by the authors according to the following procedure (example - R = Et).

The synthesis is carried out in an argon atmosphere at a temperature of 15-25 ° C with constant stirring. 430 ml of methanol, 12.3 ml (120 mmol) of acetylacetone, 10.3 ml of a 70% aqueous solution of ethylenediamine (120 mmol), 14.1 g (60 mmol) of cobalt (II) hexahydrate chloride, 19 are successively introduced into the reactor , 3 ml of a 50% aqueous solution of NaOH, 1 ml of a 2% solution of PdCl ₂ in a 1 M aqueous KCl solution, 21 ml (273 mmol) of ethyl bromide. A solution of 3.2 g of NaBH ₄ (85 mmol) in 25 ml of 5% aqueous NaOH solution was added dropwise evenly over 5 hours. After gas evolution, the reaction mixture was stirred for 1 hour. Then it is filtered, the solution is evaporated to a volume of 100 ml at a residual pressure of 10-20 mm Hg. and bath temperature not higher than 40 ° C. Then 20 g of NaBr are added and with cooling 100 ml of water and the mixture is evaporated in the same way to a volume of 100 ml. Crystallization is carried out at 0 ° C, the precipitate is filtered off, washed with 15 ml of ice water and dried in air. Then it is washed with dichloromethane (total 150-200 ml) until the green color of the wash liquid disappears. Dry the product again in air. The target product is a crystalline powder of red color. If necessary, crystallization is carried out from methanol with the addition of sodium bromide. For identification, ion-exchange TLC on SiO _{2 is used} (silofol plates, eduent - 0.1 n sodium acetate solution in methanol-water 4: 1 by volume). The purity criterion is the presence of a single spot on the plate, as well as the almost complete discoloration of the complex solution when hydrochloric acid is added. The output and value of the separation factor R _f are shown in table 1.

In the synthesis of the complexes shown in table 1, the following halide alkyls are used: ethyl bromide, n-butyl bromide, isopropyl bromide, n-amyl bromide, n-octyl bromide, n-cetyl bromide, cyclohexyl bromide, sec-octyl bromide.

The structure of the complexes is proved on the basis of ¹ H-NMR, IR spectra and analysis of acidolysis products. ¹ H-NMR spectra (solvent — D ₂ O, 200 MHz, internal standard — sodium 2,2-dimethyl-2-silapentane-5-sulfonate) of the synthesized alkyl cobalt complexes are similar to each other. The data for complex 1 (Table 1) are given below (identified signal, δ (ppm), multiplicity): CH ₃ CH ₂ Co, 0.60, t; CH ₃ —C = H, 1.70, s; CH ₃ —CO, 1.94, s; = CH, 4.98, s. The IR spectra of complexes 1–8 have characteristic absorption bands in the region of 3100–3350 cm ^–1 (narrow), which are related to NH stretching vibrations.

Analysis of the acidolysis products of the synthesized complexes 1-8, carried out by gas-liquid chromatography, TLC, and functional group tests confirms the above structural formula. The composition of the complexes is also confirmed by elemental analysis data (Table 2).

The invention is illustrated by the examples below.

PVA is obtained by saponification of PVA by any known method, for example, with alkali in an environment consisting of ethyl, or propyl, or isopropyl alcohol and water with an alcohol to water ratio of 90:10 to 40:60, while the amount of alkali is from 0.4 to 1 mol per 1 mol of vinyl acetate unit, and saponification is carried out in the temperature range from 0 ° C to the boiling point of the solvent. Sodium or potassium hydroxide can be used as alkali. Saponification of PVA is carried out to a degree of conversion of 98.0-99.9%. In the case of using branched PVA, the saponification process is accompanied by cleavage of the side chains, and the resulting PVA has a low molecular weight (low degree of polymerization).

Example 1 (according to the invention)

In a reactor with a stirrer, 100 parts by weight are mixed. vinyl acetate with an aqueous phase comprising 4 parts by weight sodium alkyl sulfonate (E-30) with a length of alkyl substituent C ₁₅ , 0.1 wt.h. initiator - complex 1 (table 1), 0.87 wt.h. KN ₂ PO ₄ and 1.24 parts by weight Na ₂ HPO ₄ (buffer system) and 200 parts by weight water. The process is carried out with stirring in a nitrogen atmosphere at a temperature of 20 ° C for 210 minutes to a conversion of 93.8%. The characteristic viscosity of the polymer solution in benzene (at 35 ° C) is 2.16 dl / g, which corresponds to a molecular weight of 850,000 and a degree of polymerization of 9880. PVA is obtained from this PVA. PVA is obtained by saponification of PVA with alkali in a medium consisting of ethyl alcohol and water, with an alcohol to water ratio of 80:20, a temperature of 30 ° C, the amount of sodium hydroxide is 0.7 mol per 1 mol of VA unit. The degree of polymerization of the obtained PVA = 6000, the degree of saponification - 99%. The degree of branching of PVA γ = 0.65.

Examples 2-10 (according to the invention).

Perform analogously to example 1, with a change in temperature, pH, type and concentration of emulsifiers, concentration of ingredients, the presence of buffer compounds and the use of complexes of alkyl cobalt (III) with tridentate ligands of various structures. PVA is obtained by saponification of PVA in the same way as in example 1.

Example 11 (prototype)

In a three-necked flask equipped with a reflux condenser and a stirrer, 300 ml of a suspension stabilizer solution (0.1% PVA solution) are added, 50 ml of VA are added in which 0.312 g (0.67%) of 1.16-hexadecane dicarboxylic acid polymer peroxide are dissolved. Suspension polymerization is carried out at a temperature of 60 ° C for 4 hours, a conversion of 94%. The resulting polymer has an intrinsic viscosity [η] = 2.41 (acetone, 30 ° C), a molecular weight of 1,187,000 and a branching ratio of γ = 2.9.

The VA polymerization recipes and process parameters, as well as some polymer properties (PVA intrinsic viscosity, molecular weight, degree of polymerization and branching, as well as degree of polymerization and degree of saponification of PVA) are shown in Table 3.

и степенью омыления.The resulting PVA is characterized by the degree of polymerization

and the degree of saponification.

The degree of polymerization of PVA is calculated by the characteristic viscosity determined in a DMSO solution at a temperature of 30 ° C according to the formula: [η] = kM _ν ^α , where k = 1.58 · 10 ^-4 , α = 0.84 [A.F. Nikolaev and other water-soluble polymers. - L .: Chemistry, Leningrad Branch, 1979, p. 34].

Determination of the degree of saponification (the content of acetate groups) in polyvinyl alcohol is carried out acidometrically according to GOST 10779-78.

The high degree of polymerization of PVA (from 6000) indicates that it can be used to produce high modulus fibers.

The data in table 3 indicate that the use of complexes of acilcobalt (III) with tridentate ligands in the emulsion polymerization of vinyl acetate allows one to obtain high molecular weight, low branched polyvinyl acetate, which can be used to produce high molecular weight polyvinyl alcohol and high modulus fibers based on it.

Table 1
Structure, yield and some properties of alkyl cobalt complexes. No. R Exit, % R _f (TCX) T _pl. *, ° C 1 Et 66 0.34 200 2 i-pr 65 ** 190 3 n-bu 64 0.40 190 4 n-am 60 0.40 180 5 cyclo-hex 41 ** 195 6 n-oct 52 0.45 160 7 sex-Oct 48 ** 150 8 n-cet 36 0.47 120 * - melting with decomposition
** - sec-alkyl cobalt complexes decompose under chromatographic conditions table 2
The elemental composition of alkyl cobalt complexes No. With
Calc. With
Found. FROM
Calc. FROM
Found. N
Calc. N
Found. O
Calc. O
Found. N
Calc. N
Found. Br
Calc. Br
Found. 1 15.97 15.92 35.79 35.93 15.18 15.22 4.34 4.30 7.05 7.00 21.66 21.71 2 15.39 15.43 37.62 37.68 14.63 14.57 4.18 4.12 7.31 7.32 20.87 20.81 3 14.84 14.90 39.31 39.28 14.11 14.07 4.03 4.10 7.56 7.50 20.14 20.12 4 14.34 14.40 40.90 41.00 13.63 13.57 3.89 3.92 7.79 7.75 19.45 19.41 5 13.87 13.92 42.37 42.32 13.18 13.27 3.77 3.73 8.00 8.03 18.81 18.73 6 13.00 13.06 45.05 45.09 12.37 12.32 3.53 3,50 8.39 8.33 17.65 17.68 7 13.00 13.06 45.05 45.09 12.37 12.31 3.53 3.52 8.39 8.34 17.65 17.67 8 10.43 10.50 53.12 53.07 9.92 9.89 2.83 2.86 9.56 9.52 14.15 14.17

Claims (3)

1. The method of producing high molecular weight polyvinyl acetate by water-emulsion polymerization of vinyl acetate in the presence of an emulsifier and an initiator, characterized in that the complexes of alkyl cobalt (III) with tridentate ligands of the general formula are used as the initiator

where R is alkyl from C ₂ to C ₁₆ , in the amount of 0.04-0.2 wt.h. and the polymerization process is carried out at a temperature of 10-40 ° C and a pH of 3.5-8. 2. Low-branched, high molecular weight polyvinyl acetate with a molecular weight of at least 850,000 and a degree of branching of 0.39-0.7, suitable for the synthesis of polyvinyl alcohol used for the manufacture of high-modulus fibers, obtained by the method according to claim 1. 3. Polyvinyl alcohol for the manufacture of high modulus fibers with a polymerization degree of at least 6000 and a saponification degree of 98-99.9%, obtained by saponification of a low-branched high molecular weight polyvinyl acetate according to claim 2.