JPS6160841B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for polymerizing an aqueous monomer solution containing acrylamide. For more details,
This invention relates to a novel polymerization method in which polymerization is carried out using an azo compound in the presence of a trace amount of peroxide. Water-soluble polymers containing acrylamide as a main component are used in many fields as flocculants and sticky agents, but their use as flocculants has recently seen rapid growth from the perspective of preventing pollution and preventing water pollution. The amount is increasing. Furthermore, nonionic, anionic, and cationic flocculants are used depending on the type of wastewater to be treated, and the performance requirements for each are becoming more sophisticated year by year. On the other hand, there are a wide variety of methods for producing these acrylamide polymers, and it is natural that they are aiming for high molecular weight, high performance, and low cost production methods. Aqueous solution polymerization can be said to be a production method that can relatively easily yield a polymer with a high molecular weight and thus meets the above objective. Many methods have been proposed for polymerizing monomers containing acrylamide as a main component in aqueous solutions, but when we examine these methods in particular regarding polymerization initiators, we find that most of them are , azo compound,
The method uses a redox initiator consisting of a peroxide or a peroxide and a reducing agent. As another example, it has been proposed to use an azo initiator and a redox initiator in combination. Polymers obtained by polymerization using these initiators are thought to have almost the same performance if they have the same molecular weight, but there are problems with solubility and long-term storage, which are thought to be related to crosslinking and molecular weight reduction. performance stability,
It is a common experience that heat resistance etc. vary slightly depending on the type of initiator. As a result of a detailed study on the relationship between the type of initiator and the physical properties of the polymer, the present inventors found that acrylamide polymers synthesized using azo compounds are superior to those using other initiators. It was found that the material was comprehensively superior in terms of solubility and long-term performance stability. Generally, high molecular weight acrylamide-based polymers can be obtained by lowering the polymerization temperature or reducing the amount of initiator through aqueous polymerization. In the case of seed polymerization systems, this is usually carried out by lowering the polymerization initiation temperature. However, lowering the polymerization temperature or decreasing the amount of initiator increases the time required for polymerization, significantly lowering productivity and increasing product cost. For this reason, a redox initiator is generally used, but as mentioned above, problems remain with respect to the stability and solubility of the polymer. In this respect, azo compounds have no problem. However, as is well known, azo compounds undergo accurate first-order decomposition without secondary reactions, but when performing low-temperature polymerization, there are no known effective substances equivalent to reducing agents in redox polymerization. It hasn't been done yet. Therefore, there are only two methods for polymerizing at low temperatures: use a relatively large amount of initiator, or introduce a sterically hindered group so that the azo compound itself decomposes at low temperatures. According to the former method, the molecular weight of the resulting polymer tends to decrease, and decreasing the amount is accompanied by a significantly longer induction period and polymerization time. Regarding the latter, various compounds have been synthesized, but they are often not produced on an industrial scale and are difficult to obtain. The present inventors conducted intensive research on a method of polymerizing commonly used azo compounds at the lowest possible temperature, and found that by adding a very small amount of peroxide, the polymerization time and induction period could be shortened. The present invention has been achieved based on the discovery that the polymerization is significantly accelerated by the above method, the polymerization proceeds extremely easily at low temperatures, and a high molecular weight polymer with excellent solubility and long-term storage stability can be obtained.
Note that a very small amount of peroxide means an amount that does not substantially cause polymerization by itself. That is, in the present invention, when acrylamide or a monomer mixture containing acrylamide is polymerized in water, the polymerization is carried out using an azo compound in the presence of a peroxide, and in this case, the amount of the peroxide used alone is substantially reduced. This is a method for polymerizing an acrylamide monomer, which is characterized in that the amount of the acrylamide monomer is such that no polymerization occurs. There are many peroxides that can be used as polymerization accelerators in the present invention, such as potassium persulfate, ammonium persulfate, inorganic peroxides such as hydrogen peroxide, t-butyl hydroperoxide,
Organic peroxides such as t-butyl peroxymaleic acid and cyclohexanone peroxide can be suitably used. In addition, as an azo compound, 2,2′-azobis-
2-amidinopropane hydrochloride, 4,
4'-azobis-4-cyanopentanoid acid, azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,
There are 2'azobis-4-methyl-2,4-dimethylvaleronitrile, etc., but 2,2'-
Azobis-2-amidinopropane hydrochloride and 4,4'-azobis-4-cyanopentanoid acid are easy to use. The amount of these azo compounds and peroxides used may vary depending on the type and purity of the monomer used, and cannot necessarily be limited, but usually the azo compound is 100 to 2000 ppm (based on the monomer aqueous solution). The amount of peroxide is 0.1 to 10 ppm, more preferably 1 to 5 ppm. In particular, if the peroxide content is less than 0.1 ppm, the polymerization promotion effect is small;
If it exceeds 10 ppm, polymerization may occur even when it is used alone, so it is difficult to obtain a high molecular weight polymer, and even if it is obtained, physical properties such as solubility and molecular weight decrease during long-term storage are undesirable. Incidentally, the above azo compound and peroxide may be used alone or in combination of two or more. Examples of the comonomer used in the present invention with acrylamide include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, and dimethylaminohydroxypropyl (meth)acrylate. Cationic vinyl monomers such as acrylate and dimethylaminoethyl acrylamide; convert these cationic monomers into quaternary ammonium salts using quaternizing agents such as alkyl halides and dialkyl sulfuric acids, and convert them into tertiary salts using sulfuric acid, etc. cationic vinyl monomers, nonionic monomers such as (meth)acrylonitrile, methyl (meth)acrylate, ethyl (meth)acrylate, and methacrylamide, and anions such as (meth)acrylic acid or their salts. sexual monomers, etc. When polymerizing these monomers or monomer mixtures, the monomer concentration is 18 to 50% by weight, preferably 20 to 35% by weight, but this range depends on the monomer composition and polymer composition. Since the properties of the polymer gel also change depending on the molecular weight, this is not a strict range. Moreover, the polymerization initiation temperature is 0°C to 40°C, preferably 10 to 30°C. Examples will be explained below. Example 1 180 g of acrylamide (crystals), 112.5 g of an 80 wt% aqueous solution of methyl chloride quaternary salt of dimethylaminoethyl methacrylate, 18.5 g of a 50 wt% aqueous sulfuric acid solution, and 30 g of dimethylaminoethyl methacrylate were dissolved in ion-exchanged water and the total amount 990
I made it g. Add this monomer mixture to 1/10NH ₂ SO ₄
After adjusting the pH to 3.5 and the temperature to 24°C, the mixture was transferred to a 1.2 dewar pin and replaced with nitrogen for about 30 minutes. Add 2 ml of ammonium persulfate 0.1% aqueous solution to this solution.
When 4 ml of an aqueous solution containing 0.6 g of 2,2'azobis-2-amidinopropane hydrochloride was added and the atmosphere was replaced with nitrogen for another 10 minutes, the temperature of the solution reached 20°C, and polymerization started after about 5 minutes. Been
Polymerization was completed in 132 minutes. The temperature of the polymer at this time was 85°C. Next, take out the polymerized gel from the dewar pin, cut this gel into udon-like pieces using a meat grinder, and then
The pellets were dried in a hot air dryer at 60°C for 16 hours, and the dried pellets were ground in a grinder to a diameter of 2 mm or less. 5 g of the obtained polyacrylamide copolymer powder
Dissolve it in 495g of ion-exchanged water and measure the viscosity using a B-type viscometer (rotor No. up to 5000CPS).
For 25000CPS or more, use rotor No. 3.
Measured at 6rpm, 25℃ (measured in the same way for each example below)
When I tried it, it was 7200CPS. There was no undissolved gel in this aqueous solution. Next, this polymer powder was heat-treated at 90° C. for 5 hours, and the viscosity of a 1% aqueous solution was measured to be 7100 CPS, and there was no insoluble gel. In addition, after storing this polymer in a plastic bag in a warehouse for about 7 months from March to October, 1%
When the viscosity of the aqueous solution was measured, it was 7000 CPS and there was no insoluble gel. Comparative Example 1 A polymerization reaction was carried out in exactly the same manner as in Example 1 except that ammonium persulfate was not added.
Polymerization started after 400 minutes of induction period and ended after 300 minutes. The viscosity of a 1% aqueous solution of this polymer is
It was 7700 CPS, and there was some undissolved matter. Comparative Example 2 A polymerization reaction was carried out in exactly the same manner as in Example 1 except that 2,2' azobisamidinopropane hydrochloride was not added, but no polymerization occurred after 24 hours. Examples 2 to 5, Comparative Examples 3 to 5 Polymerization reactions were carried out in the same manner as in Example 1, except that the polymerization initiation system shown in the attached table was used. The results are shown in a separate table along with each of the above examples. Example 6 230 g of acrylamide (crystals) was dissolved in ion-exchanged water to make a total amount of 990 g. The pH of the system was adjusted to 7.0 with an aqueous solution of caustic soda, and the monomer mixture was adjusted to 23° C., then transferred to a 1.2 Duwer bottle, and replaced with nitrogen for 30 minutes. Add 3 ml of 0.1% potassium persulfate aqueous solution and 0.3 g of 4,
5 ml of an aqueous solution containing 4'-azobis-4-cyanopentanoid acid was added, and the mixture was purged with nitrogen for another 10 minutes. Polymerization started after about 5 minutes at 20℃90
Polymerization was completed in minutes. The temperature at this time was 89°C. Thereafter, polyacrylamide powder was obtained in the same manner as in Example 1. The viscosity of the 1% aqueous solution of the obtained polymer is 3500CPS
It was hot. When a portion of this 1% aqueous solution was taken and the hydrolysis rate was measured, it was found to be 1.4 mol%. Furthermore, 10 ml of 2NH ₂ SO ₄ was added to this 1% aqueous solution, and the mixture was heated under acidic conditions (PH
When the viscosity in 2.1) was measured, it was 2400 CPS. There were no undissolved substances in this aqueous solution. Also,
This powder was heat treated at 100° C. for 5 hours to dissolve it, but there was no undissolved matter. 【table】

Claims (1)

[Claims] 1. When polymerizing acrylamide or a monomer mixture containing acrylamide in water, the polymerization is carried out using an azo compound in the presence of a peroxide, and the amount of the peroxide used is set so that the amount of the peroxide used alone is not enough to substantially polymerize. A method for polymerizing an acrylamide monomer, characterized in that the amount of acrylamide monomer is reduced to such an amount that no polymerization occurs.