DE869870C - Process for the production of synthetic rubber - Google Patents

Description

Process for the production of artificial rubber In the known Polymerization of butadiene hydrocarbons on their own or in admixture with other polymerizable substances, e.g. B. Acrylic or methacrylic compounds, styrene, Vinyl methyl ketone or fumaric acid esters, in aqueous emulsion, are initially formed Polymers with a linear molecular structure, their viscosity, d. H. Degree of polymerization, increases as the polymerization proceeds. Of a certain amount, depending on the polymerization temperature different time, z. B. when about 30 to 40% of the monomers polymerized the viscosity values begin to drop. This is a sign that the polymerization no longer proceeds with the formation of linear polymers, but a crosslinking of the molecules occurs. The polymers are then with further progress Polymerization very soon becomes insoluble, they stick together and have a high raw defo-value. At the same time, their processability and in some cases also the general ones deteriorate rubber properties. By breaking off the polymerization prematurely, one can now d. H. at the point in time when a stronger network occurs and through which one goes through can easily determine continuous viscosity measurements, the education such. Prevent inferior polymers at the expense of the yield. This way of working but is technically unsatisfactory, especially since the processability of the polymers even then, noehGl leaves much to be desired.

It has now been found that emulsion polymerization of butadiene hydrocarbons Easily processable alone or in a mixture with other polymerizable substances and masticatable synthetic rubbers with excellent technical rubber properties obtained when the emulsion polymerization in the presence of non-polymerizable makes water-insoluble solvents and during the polymerization in the Mononate soluble organic sulfur compounds, e.g. those of the type Dialkylxanthos & disulfides, mercaptans or thioethers are added.

The emulsion polymerization of butadiene hydrocarbons is known to be carried out in the presence of such sulfur compounds as regulators. Thereby products obtained that are more plastic and easier to process and in organic solvents are more soluble than those prepared in the absence of these sulfur compounds Polymers. But even they do not yet meet all the high requirements that to artificial rubbers. It turned out that the addition Such a regulator is much more beneficial when it is used during the polymerization takes place in stages. According to the present invention, there are now artificial rubbers obtained, which apart from particularly easy processability -and good general rubber-technical properties are characterized by masticatory ability, if one the organic sulfur compounds used as regulators in emulsion polymerization in the presence of non-polymerizable, water-insoluble solvents or Plasticizers added during the polymerization, preferably to one specific time.

The invention is based on the following important findings: The sulfur compounds used as regulators have a very specific effect, - Particularly when polymerizing in the absence of solvents or plasticizers clearly appears and will therefore first be explained for this case. target. Their addition causes an immediate, more or less strong, lowering of the until then- increasing strength, elasticity, defo-values and viscosity of the polymer, whereby, different from the likewise, but in a different way regulating effect the solvent or plasticizer, no drop in viscosity due to their influence occurs, the formation of lower polymers is indicated.

The steadily worsening as the polymerization progresses Damping, d. H. the degree of warming with continued strong alternating stress, as it occurs, for example, when rolling through the heavily used car tire extraordinarily improved, achieved immediately after the addition of the sulfur compounds after some time of further polymerisation a quality maximum and then becomes rapidly worse again. The masticability, for those with polymerization approaches without Solvents or plasticizers are a sales area of the incipient crosslinking, ie at about 3o to 40 0 /, polymerization conversion, a quality minimum exists, passes through shortly after the addition of the sulfur-containing regulator a maximum.

The sprayability of the mixtures goes through after the addition of the sulfur compounds also a: maximum.

The attenuation, mastication and sprayability maxima coincide and are in polymerizations in the absence of solvents or plasticizers in a sales area which is 7 to 30% higher than the sales for which the sulfur compounds were added. Are solvents during polymerization or plasticizers are present, the following picture emerges: The time of addition the sulfur compounds, the crosslinking that would otherwise expediently begin in the sales area of the molecules, can be relocated in the direction of higher sales, since j e after the amount used of the solvent or plasticizer only cross-links occurs in high sales areas or not at all. The possibility of Delaying the time at which the sulfur compounds are added its effect in terms of reducing strength, elasticity, viscosity and Defow values of the polymers are reduced.

The attenuation that can be achieved by adding the sulfur compounds and sprayability maxima are due to the damping and sprayability favoring The influence of solvents or plasticizers during the polymerization is increased. The mastication maximum is also considerably larger and is closer to Control point, d. H. the time of the addition of the sulfur compounds than in the absence of solvents or plasticizers, namely between 6 and 15% conversion from the control point calculated from.

From this it follows first of all that the addition of the sulfur compounds not at the beginning, but as soon as possible shortly before termination or termination the polymerization should take place. As also when polymerizing in the presence of solvents or plasticizers, the defo values increase slightly as the polymerization proceeds, the desired defow value can not only be achieved by adding at the appropriate time Sulfur compounds, but also by the time of = interruption of the polymerization be managed. In any case, it is essential that the time at which the Sulfur compounds at the time of termination or the end of the polymerization for the purpose of utilizing the attenuation, sprayability and mastication maxima will. As shown above, this control point is expediently up to about 30% between 6 and 15% conversion before the desired final conversion.

The sulfur compounds can also be added at intervals, however, then the quality maxima of processability and masticability and the Firmness and elasticity something return. Polymerization temperatures as low as possible have a favorable effect on the processability and masticability of the polymers the end.

The invention is explained below using a copolymer of butadiene and methyl methacrylate: Example 72 parts of butadiene, 28 parts of methyl methacrylate and 5 parts of tetrahydronaphthylcarbinol phenyl ether are dissolved in a solution of 3 parts of a medium oil sulfonate, 2 parts of paraffin fatty acid (C 14), 1.3 parts of triethanolamine and the like , i part of sodium pyrophosphate is emulsified, and the emulsion is polymerized at zo ° after the addition of 0.3 part of ammonium persulfate.

Samples are continuously taken from the batch during the polymerization. At a polymerization conversion of 44.50 / 0, 0.1 part of dibutylxanthogen disulfide is added and the polymerization continues. The following values are obtained: Sales defow value after 30 times Polymerisauone mastication duration in hours h-value raw defo-value let through % a narrow roller 9uotient a) ai 32 110, i 365o / 43 575/21 6.3 b) 27 44.5 120.3 3550/43 950/31 3.7 from 44.5 "/, conversion o, i °! o dibutylxanthogen disulfide added c 55 110.2 2 0 25/38 265/11 7.6 43 I 71 973 I 1450/37 I 240/16 `6 Properties of the vulcanizates Injectability of the modulus `` stretching untr Vulcanization mixture, rebound resilience Strength at @ . ' 0 7- ' a) moderate 47 238 696 39 49 b) bad 50 256 694 40 52 from 44.5 ° / o conversion, oi ° / o dibutylxanthogen disulfide was added c) good 47 246 I 730 37 47 d) good 44 @. 232 I 722 38 47 The modulus represents the force required to stretch the test sample to 300%. The mastication quotient is to be understood as the quotient of the raw defow value and the defow value after mastication, ie after allowing the rubber to pass 30 times through a narrow roller.

The vulcanization mixture has the following composition: 100 parts Polymer, 5 parts alcohol-soluble lignite tar extract, 1.5 parts stearic acid, 40 parts of carbon black, 5 parts of zinc white, one part sulfur, one part mercaptobenzothiazyl-2-sulfenediethylamide.

The mixture was under 2.1 atm for 60 minutes. Vulcanized vapor pressure.

The table clearly shows the beneficial effect of adding the Dibutylxanthogen disulfide, in particular the improvement of the masticability of the Polymerizats and the sprayability of the vulcanization mixture with practically constant mechanical properties. It can also be seen that with the controller addition the Rohdefowert and the K value of the polymer go down, which affects the formation very much of low molecular weight polymers due to premature chain termination under the influence of the controller. The vulcanizates are also characterized by a relatively low heating with strong mechanical alternating stress the end. The good masticability is also evident when treating the rubber in larger batches on mastication rollers, such as those used in rubber processing Technology to be used. A sufficient masticatory effect is also obtained here. The masticated rubber can easily be mixed with those required for vulcanization Mix additives and fillers. The mixtures are easy to spray and process, and the finished vulcanizates have good mechanical properties.

Claims (2)

PATENT CLAIMS: i. Process for the production of artificial rubber by polymerizing diene carbons = hydrogen alone or in a mixture with others polymerizable compounds by means of oxygen-releasing polymerization catalysts in aqueous emulsion, characterized in that in the presence of non-polymerizable water-insoluble solvents is polymerized and during the polymerization organic sulfur compounds soluble in the polymerizable compounds can be added. 2. Embodiment of the method according to claim i, characterized in that that the addition of the sulfur compounds takes place with a polymerization conversion, which is up to about 300 / ", preferably between 6 and 1501., below the desired final conversion lies.