JPH0127085B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method of producing water-soluble polymers in an aqueous medium. More particularly, the present invention relates to a process in which adverse effects caused by chelatable metal cations present as impurities in the reaction medium are minimized. A common method for preparing water-soluble polymers such as poly(acrylic acid), polyacrylamide, and their copolymers is by polymerization in an aqueous medium using free radical polymerization initiators. Molecular weight is 1,000,000 to
When producing very high molecular weight and water-soluble polymers, such as 100000000, it is important that the polymers do not contain crosslinkable networks and that the percentage of water in the polymerization medium is as low as possible to avoid unreacted products in the final product. It is desirable that the monomer content be as low as possible. In one method of producing these very high molecular weight polymers, the produced polymer solution is in a gel state that is too viscous to stir, thus resulting in significant temperatures during the polymerization reaction. ie, a temperature increase of 70°C or more. Redox systems have been used as free radical initiators that can be used over such a wide range of temperatures. However, in processes using this type of initiator, it is difficult to simultaneously achieve the above favorable results, since in order to produce very large molecular weight substances, the concentration of initiator is low. This tends to lead to an increase in free monomer content due to non-completion of polymerization, and further increases the final temperature as the solids content in the polymerization medium increases and This is because redox system components, such as persulfate/sulfite systems, react with the polymer at high temperatures to form crosslinks. Gill U.S. Patent No. 30, 1971
No. 3,573,263 teaches an improved method for carrying out such polymerization reactions, in which the initiator used includes a redox system and a source of azo compound free radicals, The reducing system is present in an amount insufficient to complete the polymerization of the ethylenically unsaturated monomer content present in the aqueous medium, and the azo compound free radical source is present in an amount sufficient to complete the polymerization reaction. exist. Preferred redox systems described in the patent specification consist of ammonium, potassium or sodium persulfates and NaH [Fe ⁺² (EDTA)], or hydrogen peroxide and NaH [Fe ⁺² (EDTA)]. It is a system. Typically the azo compound free radical source can be, for example, azobisisobutyronitrile. EDTA is ethylenediaminetetraacetic acid;
It is a chelating agent for certain metal cations. When carrying out the polymerization process of ethylenically unsaturated monomers in aqueous media using persulfates or peroxides together with NaH [Fe ⁺² (EDTA)], reproducibility in terms of polymerization time and molecular weight of the polymer There are several issues that make it difficult to obtain. In a redox system, an oxidizing agent converts ferrous ions (Fe ⁺² ) into ferric ions (Fe ⁺³ ). Ferrous ions promote polymerization, while ferric ions chain terminate polymer molecules and prevent polymerization. Ferric ions complex more rapidly with the chelating agent ethylenediaminetetraacetic acid, but ferrous ions also complex, although slower than ferric ions. If the chelating agent is present in excess, the reaction time of the polymerization is unduly prolonged due to the inhibiting effect of uncomplexed ferric ions, and the polymer molecular weight becomes low. These conclusions are based on results in which the effects of impurity cations are ignored. An even greater problem arises when polymerization reactions are carried out on an industrial scale using the above redox systems. This is because industry standard monomers contain small but varying amounts of impurities, and the water used to make the aqueous polymerization medium is also impure and varies in impurity content. An impurity that poses a particular problem is ferric ion (Fe ⁺³ ), which inhibits the polymerization reaction as described above. As a result of the presence of this impurity, its content varies widely from process to process and it is practically impossible to obtain reproducibility with respect to reaction time and molecular weight of the polymer using redox systems of the type mentioned above. . Therefore, an improved method for adjusting both the molecular weight of the polymer and the reaction time to substantially complete the polymerization when polymerizing ethylenically unsaturated monomers in an aqueous medium using a redox system. is requested. Providing such a method would satisfy a long-held need and constitute a significant advance in the art. According to the present invention, aqueous polymerization is carried out in the presence of a redox system consisting of a chelatable metal reducing agent and an oxidizing agent having reduced and oxidized forms and in the presence of an impurity chelatable cation that inhibits the polymer reaction. An improved process for producing water-soluble polymers from ethylenically unsaturated monomers by free radical polymerization in a medium is provided. This improvement consists of (1) adding to the polymerization medium a chelating agent that complexes the impurity chelatable cationic species at a faster rate than the reduced form of the chelatable metal reducing agent; The amount of said chelating agent used shall be an amount effective to overcome the inhibiting effect of said impurity chelatable cationic species; (2) said polymerization medium also contains a chelate inert to said polymerization reaction; adding a chelatable cationic species, the inert chelating cationic species having a slower rate than the impurity chelatable cationic species, but comparable or faster than the reduced form of the chelatable metal reducing agent. The rate at which the inert chelatable cationic species is added exceeds the total complexing capacity of the chelating agent. The process provided by the present invention is improved in that it allows reproducible configuration of reaction times and polymer molecular weights while maintaining a low content of unreacted monomer. It is unexpected that chelatable cation species that are inert to the polymerization reaction can be used to adjust the reproducibility of the polymerization reaction. When carrying out the improved method of the present invention, the water solubility of the ethylenically unsaturated monomers that can be homopolymerized or copolymerized ranges over a wide range from large to small, including (a) acrylic monomers; (b) vinyl alkyl ethers and (c) vinyl sulfonates; Examples include, for example, acrylic acid, methacrylic acid, acrylamide, alkyl and aminoalkyl esters of acrylic acid and methacrylic acid, such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and diethylaminoethyl acrylate, acrylic acid or methacrylate. Monoesters of acids and glycols, such as hydroxyethyl methacrylate, alkali metal and ammonium salts of acrylic acid and methacrylic acid, quaternary ammonium derivatives of aminoalkyl esters of acrylic acid and methacrylic acid, such as methyl diethylaminoethyl methosulfate methacrylate. , vinyl methyl ether, vinyl ethyl ether, and the alkali metal and ammonium salts of vinyl sulfonic acid. Redox systems useful in the improved method of the present invention are those based on an oxidizing agent and a chelatable metal reducing agent. As the oxidizing agent, persulfates such as ammonium persulfate, sodium or potassium persulfate, or hydrogen peroxide are preferably used, but these are not necessarily required. As the metal reducing agent capable of chelating, those having a reduced type and an oxidized type are used. Preferred chelatable reducing agents are salts such as ferrous sulfate or double salts such as ferrous ammonium sulfate. The principles of the invention apply to other oxidant compositions as well as other chelatable metal reducing agents of the type described. The present invention does not require the use of an azo compound free radical source in conjunction with a redox system, although this can be done if desired. Suitable azo compound free radical sources include, for example, azobis(isobutyronitrile). Other well known azo compounds are also useful. The present invention also requires a chelating agent that complexes the impurity chelatable cationic species at a faster rate than it complexes the reduced form of the chelatable metal reducing agent. Many chelating agents can be used to meet these requirements. A preferred chelating agent is ethylenediaminetetraacetic acid. The amount of chelating agent to be added to the polymerization medium at the beginning of the polymerization can be any amount effective to reduce the effect of inhibiting impurity chelatable cationic species. The amount of impurity chelatable cationic species can be easily determined, and an amount of chelating agent that will complex at least half of this amount can be used. In preferred embodiments, the amount of chelating agent used is at least equal to or greater than the amount required to complex the total amount of impurity chelatable cationic species. An excess of the inert chelatable cationic species over the complexing capacity of the chelating agent is also added so that the excess chelating agent so used will not have an adverse effect on the polymerization reaction. The present invention also requires the use of a chelatable cationic species with a chelating agent that is inert to polymerization in the polymerization medium. This cationic species must be complexed at a slower rate than the impurity chelatable cationic species, but at a rate comparable to or faster than the reduced chelatable metal reducing agent. Any chelatable metal cation species that neither promotes nor inhibits the polymerization reaction can be used. A preferred species is the zinc cation (Zn ⁺² ). The amount of inert cationic species to be used is at least equal to the total complexing capacity of the chelating agent, preferably in excess. At least 2 of the complexing capacity of the chelating agent
A double or higher excess has been found to be preferable.
Other ions such as lead and at pH 3-6
Ions with lower stability constants than Fe ⁺³ /EDTA can also be used. The impurity chelatable cationic species that inhibit polymerization are primarily ferric (Fe ⁺³ ) and cupric (Cu ⁺² )
ion, but the same applies to other cationic species. The amount of impurity cation species is usually approximately
It can vary widely from 0.1 to about 1.5 ppm parts. The present invention provides a method that is effective with or without the presence of impurity cation species. However, when operating on an industrial scale, it is practically impossible to prevent the formation of impurity cations, so the process is generally carried out in the presence of such impurities. Impurities may originate from the monomer content used and/or the water used to provide the polymerization medium. Although the impurity content can be determined by analysis, it is desirable to be able to operate without waiting for the results of such analysis. Although the present invention has a wide range of impurity content tolerances, it remains an improved process. As mentioned above, the aqueous polymerization medium can contain a single monomer, such as acrylamide, or a mixture of copolymerizable monomers, such as dimethylaminoethyl methacrylate and acrylamide. Polymerization of the monomer-containing material present in the aqueous medium can be carried out under conditions used in the art. Thus, for example, in some methods the aqueous medium containing the monomers and the equipment used are purged with N ₂ or CO ₂ or other inert gas before adding the polymerization initiator. The invention will be further illustrated by the following examples.
In these examples, all parts and percentages are by weight unless otherwise specified. Comparative Example A The procedure of Example 3 of US Pat. No. 3,573,263 was repeated using the polymerization initiator described below. A 32.5% aqueous solution consisting of 15 mol% dimethylaminoethyl methacrylate quaternized with methyl chloride and the remainder acrylamide was prepared at pH 3.0. 200 g of this solution in a vacuum flask was purged with nitrogen and the following initiators were added: 21 ppm FeSO ₄ (NH ₄ ) ₂ SO ₄ 6H ₂ O 12 ppm ammonium persulfate 200 ppm azobisisobutyronitrile Polymerization reaction The system contained 0.3 ppm Fe ⁺³ as an impurity. Polymerization took 300 minutes and generated an exotherm of 64°C.
The resulting polymer exhibits a standard viscosity of 3.55 cps, 1M
This was determined by measuring a 0.1% aqueous solution of the polymer in NaCl using a Bruckfield viscometer at 25°C. Comparative Examples B, C, and D In three additional examples, the procedure of Comparative Example A was repeated, except that in each example an increased amount of Fe ⁺³ cation was added with the polymerization initiator. Ta. The details and results are shown in Table 1.

[Table] The results show that small amounts of Fe ⁺³ reduce the standard viscosity (indicative of molecular weight) of the polymer, increase the time required to complete the polymerization reaction, and lower the exothermic temperature. Comparative Examples E-J The procedure of Comparative Example A was repeated in eight additional tests. In this separate test, we added
Various levels of Fe ⁺³ ions are maintained at a constant level.
A complex of Zn ⁺² /EDTA was added. The details and results are shown in Table 2. Note that Zn ⁺² /EDTA is added by adding the required amount of water-soluble Zn salt (e.g. zinc sulfate) before polymerization.
The method was carried out by adding EDTA and EDTA to the reaction medium to generate a complex compound in situ. The same applies to the following examples.

[Table] These results show that the reaction time and viscosity increase when using the Zn ⁺² /EDTA complex compound. Examples 1 and 2 The procedure of Comparative Example A was repeated in three additional test examples. One test example repeats the standard process, the second test example uses Zn +2 /EDTA and excess Zn +2 ions without the addition of Fe ⁺³ ions, and the third test example uses Zn ⁺² /EDTA and excess Zn ⁺² ions. Fe ⁺³ ion,
Zn ⁺² /EDTA and excess Zn ⁺² ions were added. The details and test results are shown in Table 3.

[Table] These results demonstrate that using sufficient Zn ⁺² /EDTA complexes together with excess Zn ⁺² results in shorter reaction times and reproducible higher viscosities. . Example 3-10 Monomer content was quaternized with methyl chloride
25 mol% dimethylaminoethyl methacrylate and
The procedure of Examples 1 and 2 was repeated except that the monomer solution was 75 mole percent acrylamide and the monomer solution contained 40 percent monomer. The details and results are shown in Table 4.

【table】

[Table] * Too low to measure These results indicate that in the presence of impurity Fe ⁺³ ions, the combination of Zn ⁺² /EDTA and excess Zn ⁺² shortens polymerization time and increases viscosity. show. Examples 11-18 The procedure of Examples 1 and 2 was repeated using 15 mole % dimethylaminoethyl methacrylate quaternized with methyl chloride and 85 mole % acrylamide. The initiator system was 3 ppm Fe ⁺² , 12 ppm ammonium persulfate and 200 ppm azobisisobutyronitrile. A series of six examples uses a constant content of Zn ⁺² /EDTA and an excess of Zn ⁺² ions.
This was done by varying the amount of impurity Fe ⁺² ions added. A control study was also performed. The results and details are shown in Table 5.

TABLE These results show that higher viscosities and shorter reaction times can be achieved with the improved process of the present invention. Examples 19-24 Quaternary monomer 10 used in Examples 1 and 2
Example 1 using mole % and remaining acrylamide
Steps 2 and 2 were repeated. The reaction mixture contained 40% by weight monomer. The initiator system used was 3ppm Fe ⁺² , 12ppm ammonium persulfate and
It was 400 ppm azobisisobutyronitrile.
The initial pH was 3.0 and the initial temperature was 5°C. The details and test results are shown in Table 6.

[Table] The results show that increasing the amount of chelating agent containing excess zinc ions increases the standard viscosity and shortens the reaction time. Example 25-32 Again following the procedures of Examples 1 and 2, using 25 mol% of dimethylaminoethyl methacrylate quaternized with methyl chloride and the remainder acrylamide,
A series of tests were carried out using a reaction medium containing 40% by weight of monomer. The initial pH was 3.0 and the initial temperature was 0°C. The details and results are shown in Table 7. These results again demonstrate the increased standard viscosity and shortened reaction time afforded by the present invention.

【table】

Claims (1)

[Scope of Claims] 1. In the presence of a redox catalyst system comprising an oxidizing agent and a chelating metal reducing agent having a reduced form and an oxidized form, and also monomer and/or polymerization Production of water-soluble polymers from ethylenically unsaturated monomers by free radical polymerization in an aqueous polymerization medium in the presence of polymerization-inhibiting impurity chelatable cationic species contained in the catalyst (1) adding a chelating agent to the polymerization medium that complexes the impurity chelatable cation species at a faster rate than the reduced form of the chelatable reducing agent; (2) further adding to said polymerization medium a chelatable cationic species inert to said polymerization, with the proviso that said inert chelatable cation species complex at a rate slower than said impurity chelatable cationic species but comparable or faster than the reduced form of said chelatable metal reducing agent, and the amount of said inert chelatable cationic species is less than said chelatable cationic species. An improved method of producing a water-soluble polymer in an amount that exceeds the total complexing capacity of the agent. 2. The method of claim 1, wherein the chelatable metal reducing agent is ferrous ammonium sulfate. 3 The inert chelatable cation species is Zn ⁺²
The method according to claim 1. 4. The method of claim 1, wherein the polymerization medium comprises a source of azo compound free radicals. 5. The method according to claim 1, wherein the azo compound radical source is azobisisobutyronitrile. 6. The method according to claim 1, wherein the ethylenically unsaturated monomer-containing material is a mixture of dimethylaminoethyl methacrylate quaternized with methyl chloride and acrylamide. 7. The method of claim 1, wherein the chelating agent is ethylenediaminetetraacetic acid.