DD154702A1 - METHOD FOR PRODUCING BUTADIENIC ACRYLNITRILE COPOLYMERISES - Google Patents

Abstract

The invention includes a process for the preparation of butadiene-acrylonitrile copolymers by free-radical emulsion polymerization using emulsifiers based on natural or synthetic carboxylic acid salts, such as resin and fatty acid soaps alone or combined with each other in any proportions, with or without the addition of conventional emulsifiers and / or dispersants. These copolymers serve as vulcanizable elastomers preferably for the production of oil and solvent-resistant rubber articles. The aim of the invention is to produce copolymers of butadiene and acrylonitrile with gross acrylonitrile contents of 10 wt .-% to 30 wt .-%, which is characterized by good Elastizitaets- and low-temperature rubber properties combined with increased swelling resistance and advantageous processability distinguished. The object is achieved in accordance with the invention by controlling the reaction course of the butadiene-acrylonitrile copolymerization by means of a specific metering regime for monomers and / or molecular weight regulators expediently determined by computer program and working up the latices prepared by this process by coagulation in an acidic medium to give the solid rubber.

Description

Process for the preparation of butadiene-acrylonitrile-Cppolym erisaten

Application of the invention

The invention relates to a process for the preparation of butadiene-acrylonitrile copolymers having good elastic and low-temperature rubber properties and increased resistance to flow and advantageous processability with gross acrylonitrile contents of 10 wt .-% to 30 wt .-% by free radical emulsion polymerization Use of emulsifiers based on natural or synthetic carboxylic acid salts, as in spielst eise resin and / or fatty acid soaps alone or combined with each other in any proportions, with or without the addition of other conventional emulsifiers and / or dispersants »After large-scale workup of these latices by, for example, coagulation in acidic medium serve these

Copolymers of butadiene and acrylonitrile as vulcanizable elastomers preferred for the production of oil and solvent resistant rubber articles.

Characteristic of the known technical solutions

The preparation of synthetic rubber latices by free-radical emulsion polymerization using emulsifiers or emulsifier combinations based on carboxylic acid salts is known in principle (CW Carr et al., Journ. Polynu Sei £ (1950), 191 et seq. "K. Möbius, Gum, Asbestos , Plastics 22 0969) »7 ff). The synthetic rubber can be isolated in a known manner from the latexes after addition of acids and / or electrolyte solutions and / or synthetic coagulants by cascade or screw coagulation and subsequent drying of the pre-dewatered rubber crumbs (AP Kroutschkowi "General Technology of Synthetic Rubbers", S. 355 ff, Publisher "Chimia", Moscow

P.A. Kirpitschnikow et al .: "Chemistry and Technology of Synthetic Rubber", p. 393 et seq., Publisher "Chimia", Leningrad 1970 $

OB, Litvinj "Fundamentals of the Technology of Rubber Synthesis * ¹ p." 292 ff, Publisher "Chimia", Mpskau 1972 $ IW Garmonpw: "Synthetic Rubber", pp. 255 ff, publisher "Chimia", Leningrad 1976).

The resin and / or fatty acid soaps used in the polymerization as emulsifiers are converted into the acids during coagulation in an acidic medium and therefore remain in the polymer.

The content of free resin acids, as known, improves the ready-to-use tack of the rubber.

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In the case of the polymers prepared by these known processes, in particular in the case of butadiene-acrylonitrile copolymers of low gross acrylonitrile contents (10% by weight to 30% by weight), a number of disadvantages occur in the property profile.

The low acrylonitrile incorporation levels synthesized by the previously known processes butadiene-acrylonitrile rubbers have good elasticity and low temperature properties, but show a significant decrease in the oil and solvent resistance and the processability.

The degree of stability of the butadiene-acrylonitrile copolymers to aliphatic and aromatic hydrocarbons and their processability depend essentially on the gross acrylonitrile content, the chemical uniformity, the height of the average molecular weight, the molecular weight distribution, the branching and crosslinking fractions, the type of Monomer arrangement in the polymer chain and the microstructure from.

Especially when using butadiene / acrylonitrile starting monomer ratios relatively far below the azeotropic composition, the molecular parameters and the sizes which affect the chemical uniformity and composition of the copolymers affect the swelling resistance and workability properties. The presence of rubbers and / or fatty acids in the rubber, which are used in the form of their soaps as emulsifiers, is expected to degrade the properties, especially the swelling resistance. It is with the previously known methods according to Jap. PS No., 45 - 13 106; US-PS No.-. 2 623 032 $ Franz. PS No. 1 018 413 \ DE-OS 2 554 268 has not succeeded in obtaining a low acrylonitrile-containing rubber with a balanced ratio of swelling properties and processability at low temperatures and producing elasticity when using carboxylic acid salts as emulsifiers.

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Object of the invention

The aim of the invention is to produce copolymers of butadiene and acrylonitrile by free-radical mechanism using carboxylic acid salts, such as resin and / or fatty acid soaps as emulsifiers, which have gross acrylonitrile contents of 10 wt .-% to 30 wt .-% and characterized by good elasticity and low temperature properties combined with increased swelling resistance and advantageous processability.

The aim is to eliminate the deficiency of the known production methods.

Dar interpretation of _We sens ^ of Erf indung

The invention has for its object to develop a process for the preparation of butadiene-acrylonitrile copolymers with low gross acrylonitrile contents, wherein the above requirements are to be met. The object is achieved in that a conjugated diene, preferably butadiene and a polar vinyl monomer, preferably acrylonitrile, in a conventional manner a radical copolymerization in the presence of natural and / or synthetic carboxylic acid salts, such as resin and fatty acid soaps, alone or with each other in any Combined ratios, as emulsifiers, in the presence of free-radical or redox initiators and molecular weight regulators at temperatures from ^{0 0} C to 50 ⁰ C, preferably j ° C to 35 ° C> to reaction conversions of 40% to near 100%, preferably 60 % to 80%, are subjected and the course of the reaction · is controlled in a targeted manner by a dosing regime for the reaction components determined by means of a computer program. For example, in the case of butadiene-acrylonitrile copolymers having a gross acrylonitrile content of 10% by weight to 30% by weight in the property picture, an ideal combination of good elasticity and low-temperature properties with improved swelling resistance and processability, despite the presence of

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To achieve senheit of egg emulsifier ingredients in the form of their free acids, a calculated by calculation program taking into account the set Ausgangsmonomerverhältnisses, the polymerization temperature, the reaction end conversion and the polymerization rate Nachdosierungsregime for monomers and / or initiator and / or molecular weight regulator and / or emulsifier solution in the copolymerization is applied. The subsequently synthesized latices are coagulated in acidic medium and worked up in a known manner to butadiene-acrylonitrile rubbers.

According to the process of the invention, the reactants can also be used individually or in a changed order. Be added to the calculated proportions at different conversions or at the beginning of the copolymerizing system.

As a further essential feature of the process according to the invention, the emulsifier constituents converted into free acids by the coagulation in an acidic medium can remain in the rubber and likewise contribute to the modification of the polymer properties. The method of the present invention is applicable to the preparation of a variety of conjugated diene-vinyl compound copolymers by taking into account the copolymerization behavior of the monomers used, the related dependence of the monomer incorporation ratios on the conversion, and the changes in reaction rate during the copolymerization. The rubbers prepared by the novel method can emulsion copolymers of conjugated dienes, for _o example, 1,3-butadiene, isoprene, chloroprene and monoäthylenisehen compounds, for example, acrylonitrile be. The initiators which can be used are the known radical-providing substances, such as peroxy or azo compounds or redox systems.

As molecular weight regulator for the process according to the invention-the known long-chain aliphatic

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Mercaptans, e.g. tertiary Dod.ecylr.ierc apt used.

Taking into account the transfer constant which is valid for the system used and the dependence on the temperature of the starting monomer, it is also possible to use other conventional regulators for the process according to the invention, such as dialkylxanthogen disulphides, branched or unbranched aliphatic mercaptans, aromatic mercaptans or unsaturated thioethers. As emulsifiers of the process according to the invention, the alkali salts of natural carboxylic acids, for example animal fatty acids and disproportionated resin acids prepared from rosin and / or tall resin alone or in combination with one another in any proportions, are used

The alkali metal salts of synthetic carboxylic acids are also useful as emulsifiers alone or as blends with natural carboxylic acid soaps.

By applying the method according to the invention, the chemical uniformity of the copolymers are favorably influenced and achieved for the processability of the butadiene-acrylonitrile rubbers advantageous adjustment of the molecular parameters.

It is surprising for the skilled worker that, despite a certain Eestemulgatorgehaltes, predominantly in the form of the free acids in the polymer good elastic and cryogenic properties associated with increased resistance to swelling im.Vergleich to a prepared by conventional methods copolymer of the same gross acrylonitrile content are found

A particular advantage of the process according to the invention is furthermore that, in contrast to conventional processes, an increased temperature or concentration at the beginning of the reaction is not required. A dosing regime based on this invention is guaranteed for the reaction components when considered the optimum polymerization temperatures and reaction conversions for a particular property

bare and reaction-technically well controlled rate of polymerization over the entire course of the reaction.

This advantage of the method according to the invention also results in the possibility of increasing the space-time yield while simultaneously improving the rubber properties, which is also surprising to the person skilled in the art.

An essential advantage of the method according to the invention is that the resin and / or fat acid used as emulsifiers se remain after coagulation as acids in the rubber, so not like other emulsifiers are washed out and thus in conjunction with the indicated good properties to a Improve the economy of the process while avoiding the wastewater pollution caused by the washed out emulsifier.

Embodiment "

81 parts by weight of butadiene and 19 parts by weight of acrylonitrile, of which 12.5 parts by weight are initially charged at the beginning of the reaction, and 6.5 parts by weight are metered in at a reaction conversion of 35 %, in a continuous polymerization plant. using 3 _t 5 parts by weight of an emulsifier mixture of disproportionated abietic acid and a natural carboxylic acid of average chain length from C 1 to CUg in the form of the potassium salts in a weight ratio of 1: 1 at pS = 10.5, with the addition of a radical-forming solvent Initiator, for example, potassium peroxydisulfate, a chain-transferring acting molecular weight regulator, for example tertiary dodecylmercaptan, of its use amount 0.27 parts by weight submitted to the beginning of the reaction, 0.15 parts by weight at 20 % conversion and 0.07 parts by weight 40 % conversion are added, subjected to the copolymerization. The reaction is carried out at 35 ° C until a conversion of SO %

carried out.

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This gives a precipitate-free latex which, after coagulation in an acidic medium and on an industrial scale, gave a rubber having a gross acrylonitrile content of 18.7% by weight and a Mooney viscosity of ML

In the performance test of the vulcanized rubber (vulcanization: 20 min · at 143 ^° C.) the following values typical for the process according to the invention were determined:

Buna NB-Tied Glass Over-Rebound Swell

Ί?

Sample acrylonitrile gear temp. ) Elasticity resistance)

A 18,7 -39 48 52,1

B 18,6 -37 46 57,2

The Mooney viscosity for the product was A ML and for the product B ML ^ ^ n = 53 »

A = test product according to the method according to the invention B ss comparison product (prior art)

1 ·

) The low temperature behavior was determined by determining the

• Glass transition temperature tested according to the static torsion method

) Mass change after 72 hours at 20 ° C in isooctane / toluene 7/3 solvent

From the performance parameters of the synthesized by the process according to the invention butadiene-acrylonitrile - copolymer (Buna ITB sample A) results in a property image that characterized by increased resistance to swelling at the same time good elastic and low-temperature properties we characterize

Claims (1)

22SA A5 invention claim A process for preparing butadiene-acrylonitrile copolymers with good elasticity and low-temperature rubber properties and increased swelling resistance and advantageous Verarbeitbarke it with gross-acrylonitrile contents of 10 wt _o -% to 30 wt _o -% by free-radical emulsion polymerization at temperatures of O ⁰ O to 5O ⁰ C up to reaction conversions of 40 % to near 100%, preferably 60 % to 80%, in the presence of molecular weight regulators and emulsifiers based on natural or synthetic carboxylic acid salts, such as resin and fatty acid se ifen alone or together any proportions combined, with or without the addition of other conventional emulsifiers and / or dispersants, characterized in that the Eeaktionsverlauf the copolymerization depending on the target gross acrylonitrile content by a certain, conveniently determined Bechenprogramm dosing regime for monomers and / or molecules rgewichtsregler controlled and the latices prepared by this process are worked up by coagulation in an acid medium to Eestkautschuk, wherein, for example, for preparing a butadiene-acrylonitrile copolymer with 19% bound acrylonitrile at 80% conversion to a-Ausgangsmonomerengemisch consisting of 81 wt _o parts by butadiene and 12.5 parts by weight of acrylonitrile at 10 % to 60% conversion, preferably 25 % to 45 % conversion, 6.5 parts by weight of "acrylonitrile, preferably in emulsified form, added and as a molecular weight regulator, for example, 0.49 wt _o -terminated tertiary dodecyl mercaptan, of which 0.27 parts by weight are initially charged at the beginning of the reaction, 0.15 parts by weight, at 15 % to 35% conversion, preferably 20 % to 25% conversion, and 0, 07 parts by weight at 35 % to 60 % conversion, preferably 35% bi-s 45 % conversion, can be added. ·;