SU998476A1 - Process for demonomerizing latexes of synthetic polymers - Google Patents

Abstract

In PVC prepn. by vinyl chloride suspension polymerisation under pressure in an agitator-reactor, the monomer is dispersed in the aq. phase with the addn. of polymerisation initiators, macromolecular emulsifiers, tensides and further addtives. At least 2 wt.% of the tensides in polymerisation mixt. consist of insoluble salts, (I), of 8-20 C carboxylic acids, contg. at least one unsaturated bond, with di- or polyvalent metal cations. W.r.t. vinyl chloride, the concn. of (I) is pref. 0.002-0.2 wt. %. The polymer particles have good morphology and high porosity, achieved with less than half of previously used tenside concns. Bulk wt. does not decrease appreciably with increasing porosity.

Description

The invention relates to a method for the de-ionization of the latexes of synthetic polymers whose glass transition temperature is above 50 ° C. Such polymers include, for example, polystyrene, high styrene resins, styrene-acrylonitrile copolymers, grafted acrylonitrile-styrene-styrene polymers (LAN) or graft copolymers methyl methacrylate-styrene-butyl acrylate.

Upon receipt of the latexes of these polymers, it is often for various reasons that it is necessary or desirable to bring emulsion polymerization only to a certain degree of conversion. The unreacted monomers and other volatile substances are then removed from the latexes by distillation.

Known methods for the demonization of the latexes of synthetic polymers are based on batch or continuous stripping with iodine vapor or in the presence of an inert gas such as, for example, described in the patent of GDR 191363.

In accordance with British Patent No. 1090976, latex is mixed in the form of droplets with water vapor, which condenses on these drops. According to British Patent 1205776, the effectiveness of the demonomerization process is improved by carrying out a process in which the latex is mixed with rapidly flowing gas, such as water vapor, so that a large liquid-gas phase boundary is formed as a result of turbulent mixing.

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In all the described processes, the nature of the temperature dependence and the rate of de-monomerization remain practically without significant changes. While for latex elastomer with a low temperature Tp it is possible to choose the demonomerization temperature in rather wide intervals without significant influence on the demonomerization rate of the latexes, in latexes with a higher glass transition temperature Tj. with a decrease in temperature during demonomerization under temperature T, a significant decrease in the rate of the process is observed. In production, it is usually necessary to find an acceptable compromise between the kinetics of the process and the undesirable consequences of an elevated operating temperature during demonization, to which. These include, for example, accelerated polymer aging during the process, large heat losses and large losses of returnable monomers as a result of their additional polymerization. This deficiency of the known coutodon can be significantly limited by the invented method. In accordance with the invention, the monomerization of latexes synthetically polymers, whose glass transition temperature is higher, is produced by a race with water vapor or an inert gas, so that 0.5-10 wt.% Is added to the latex before the start of the de-monomerization process. solvent, based on polymer polymer latex. The softener may be added to the latex in the form of an aqueous emulsion. At the same time as the softener, some or all of the anti-aging agent can be added to the latex. By softener is meant a substance which, at the de-monomerization temperature, is in a liquid state and is mixed at this temperature with the polymer of a given latex sufficiently so that all the amount introduced can be mixed with the polymer, i.e. they are meant as softeners of polymers. in the usual sense of this, f (dib tyl phthalate, butyl phthalate, tricresyl phosphate, trichloroethyl phosphate, propylene glycol stearate), and other substances that may have a softening effect on the current Limer, such as medical oil, toluene, or ethylbenzene. The softener is a common additive that is added to the polymer. In most cases, this is done at the end of the technological process, i.e. the softener is introduced into the divided polymer. When choosing a softener, the purpose of the latex after the de-monomerization is performed is taken into account. Technological design of the de-monomerization process is not practical when using the invention. The method can be used in a periodic and continuous process, during which thickening and dilution of the final latex can occur. The advantage of the method according to the invention in comparison with the known methods is an increase in the speed of demonstration at a constant temperature or a decrease in the temperature of the demononization while maintaining its speed. In both these cases, when using the method according to the invention, the energy consumption can be reduced. This equipment also reduces polymer aging during the technological process. Example. In a stripper reactor with a volume of 20 liters, vacuum de-monomerization of polystyrene was carried out. latex with an average particle size (determined turbidimetrically) d 246 nm and an initial content of free styrene 5 wt.% calculated on the total amount of polymer + monomer, for 60 min, at. The initial dry matter content in the latex is 24.1%, the steam temperature at the reactor inlet, the steam flow rate into the reactor is 1.3 kg / h, i.e. 0.16 kg of steam / kg of latex / h, the speed of mixing of the latex at demonomerization is 54 rpm After 60 min of demonomerization, the free styrene content was found to be 2.0% per sum. polymer + monomer. The dry matter content of the latex remains unchanged. EXAMPLE 2: The latex was demononized in the same way as in Example 1, but an emulsion of 9 parts by weight was added to the starting latex before the start of the demonomerization. butyl stearate, 1 weight.h. 2,6-ditertbutyl-4-methylfenol, 0.3 weight.h. sodium dodecylbenzene sulfonate and 10 wt.h. water per 100 h, polymer. After 60 min of demonomerization, the free styrene content in the latex was found to be 1.1% based on the sum of the polymer and styrene. Example 3. The equipment described in Example 1 was used to demolish ABC latex containing 85% styrene-acrylonitrile copolymer and 15% polybutadiene, with an initial dry matter content of 27.2%, at a pressure of 26.6 kPa and a steam feed rate of 1, 3 kg / h After 60 minutes of de-monomerization, the styrene content decreased from an initial 4.6 wt.% To 1.41 wt.% Based on the amount of polymer + monomer. When repeating the experiment in the presence of 2 weight.h. butyl stearate and 1 weight.h. propylene glycol stearate, which are added to the latex in the form of a 50% aqueous emulsion with 0.5% sodium oleate, after 60 minutes of demonomerization in the latex, only 1.1% of free styrene was found, calculated on the amount of polymer + monomer. Example 4. On the equipment described in Example 1, a vacuum demonomerization of the latex was carried out, the polymer of which contained 50 wt.h. copolymer of butadiene-butyl acrylate and 50 weight.h. polymethyl methacrylate. The initial dry matter content in the latex is 30% and the initial content of methyl methacrylate in the latex is 10% based on the sum of the weights of the polymer and methyl methacrylate. The latex was subjected to demonomerneation with a mixture of water vapor and nitrogen with a volume ratio of 10: 1 for 30 minutes. Then an emulsion of 3 parts by weight was added to the latex. Dbutylphthalate and 2 wt.h. ethylbenzene in 5 weight.h. water. After 60 minutes of demonomerization, counting from the beginning of the process, 2.5% of monomeric methyl methacrylate was found in the latex at 65 ° C, while the content of methyl methacrylate was found to be 2, .2% without the addition of smoker and under the same identical conditions.

From a comparison of the results given in examples 1-4, a significant increase in the rate of kinetics of the process in the presence of a softener in latex is evident.

Claims (3)

1. A method for demonizing the latexes of synthetic polymers whose glass transition temperature is T above, by distillation with steam or its mixture with an inert gas, characterized in that 0.5 to 10% by weight of softener, calculated on the weight of the polymer in latex, is added to the latex before the process of demonomerization or during it. 2. A method according to claim 1, characterized in that the softener is added in the form of an aqueous emulsion: -: ii. 3. Method according to Claims 1 and 2, which is based on the fact that some or all of the anti-aging agent is added together with the softener. It is recognized as an invention on the results of the exgertizy implemented by the Office for the Invention of the Czechoslovak Socialist Republic.