JPS62174216A - Production of n-methylolacrylamide/acrylamide copolymer - Google Patents

Abstract

PURPOSE:To obtain the title copolymer having a very high MW and excellent stability and water solubility, by neutralizing N-methylolacrylamide obtained by reacting formic acid-free HCHO with acrylamide in basic conditions and polymerizing the monomer. CONSTITUTION:HCHO of a formic acid content <=100ppm is obtained by dissolving formaldehyde generated by heating, e.g., paraformaldehyde to about 150 deg.C in cold water. 0.1-5mol of this HCHO substantially free of formic acid is reacted with 1mol of acrylamide by using a basic compound (e.g., NaOH) as a catalyst at 10-90 deg.C and a pH adjusted to 8-12 to obtain N- methylolacrylamide, while controlling the formation of a cross-linkable substance such as N,N'-methylenebisacrylamide. In a neutral buffered solution formed by adding an acid to the above reaction solution, the monomer is polymerized at 10-90 deg.C in the presence of 0.005-5wt% radical polymerization initiator.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing an N-methylolacrylamide-acrylamide copolymer.

The N-mesololamide-acrylamide copolymer or a polymer copolymerized with other vinyl monomers can be widely applied to aqueous solutions or hydrophilic polymers.

[Conventional technology and its problems]

Homopolymers of N-methylolacrylamide or copolymers with other vinyl monomers have been known for a long time.

However, conventional N-methylolacrylamide monomers contain many impurities, especially crosslinkable substances such as N and N'
- Since the content of methylenebisacrylamide is 20 ppm or more based on the weight of N-methylolacrylamide, it is difficult to obtain a linear and high molecular weight polymer as it is.

[Means for solving problems]

An object of the present invention is to provide a method for producing high molecular weight N-methylolacrylamide and acrylamide copolymers.

The above object of the present invention is to form N-methylolacrylamide by contacting formaldehyde that does not substantially contain formic acid with acrylamide under basic conditions, and then neutralizing it by adding an acid to the reaction system. This is achieved by a method for producing an I-methylolacrylamide-acrylamide copolymer, which is characterized by carrying out polymerization.

The high molecular weight H-methylolacrylamide-acrylamide copolymer is a high-purity ON-acrylamide copolymer that does not contain crosslinking substances.
Obtained by using methylol acrylamide and acrylamide mixed monomers.

Crosslinking substances, especially N! - In order to obtain said mixed monomers free of methylenebisacrylamide, the inventors have found that it is necessary to contact acrylamide with formaldehyde substantially free of formic acid under basic conditions.

In order to obtain a highly pure N-methylolacrylamide monomer, formaldehyde substantially free of formic acid is used, but the content of formic acid is preferably as low as possible, and is usually 0.00 ppm or less based on the weight of formaldehyde.

Formaldehyde substantially free of formic acid may be used, e.g.
It can be obtained by heating ld paraformaldehyde to 750°C and dissolving the generated formaldehyde in cold water. Alternatively, formaldehyde may be supplied to the reaction system in gaseous form. However, this objective can be easily achieved by a simple operation in which formic acid in an aqueous formaldehyde solution is neutralized in advance with a base and used as a formate.

As the base used for neutralizing formic acid, any common basic compound can be used. Examples include hydroxides of alkali metals, alkaline earth metals, μ-class ammonium, etc., tertiary amines, and weakly basic salts consisting of strong bases and weak acids. May be used.

As for the base used for neutralization, it is desirable to add a base equivalent to that of formic acid. Further, in order to avoid the production of formic acid due to the Cannizgaro reaction as much as possible, the temperature during neutralization should be lower, preferably 21° C. or lower, and it is desirable to use the neutralized reaction product immediately.

Acrylamide is typically used as an aqueous solution in the range of 10 weight to saturated solutions.

The concentrations of formaldehyde and acrylamide are appropriately combined and used so that a uniform aqueous solution is obtained in the reaction system after contact.

The ratio of formaldehyde to acrylamide used in the reaction ranges widely from 0.1 times mole to 3 times mole.

Any common basic compound can be used as a catalyst for the reaction of acrylamide and formaldehyde. Specifically, a basic compound similar to the base used to neutralize formic acid in formaldehyde, and an ion exchange resin that acts on strong or weak basicity are used.

The amount of the basic compound used as a catalyst for the reaction varies depending on its basicity, and is therefore regulated by the pH of the reaction system. Usually the pH of the reaction system is r~/0, preferably 2~/0.
It is added and used so that it becomes the evening range.

The reaction temperature of acrylamide and formaldehyde is 1o-
It can be selected within a wide range of yo°C, but from the viewpoint of suppressing side reactions, it is preferable to set it within a range of plo-70°C.

In addition, the formation of N, ``-methylenebisacrylamide is very slow under basic conditions, but it is gradually formed during long-term storage, so after the methylolation reaction is completed, the basic compound used as a catalyst should be immediately It is desirable to harmonize.

When neutralizing the basic compound of the catalyst, any common acidic compound can be used. Examples include mineral acids and organic acids, but preferably weak acids or weak acid salts are used.

The reaction between acrylamide and formaldehyde can be carried out using any reactor according to the conventionally known 6-bar format, but a preferred reaction method is to charge an aqueous acrylamide solution and a catalyst in a stirring tank, and to react with the reaction mixture under stirring. This is a method in which an aqueous formaldehyde solution containing substantially no formic acid is added dropwise.

In the method of the present invention, N, N
It contains unreacted acrylamide including '-methylenebisacrylamide, and therefore a copolymer of N-methylolacrylamide and acrylamide is obtained.

As the solvent used in the polymerization reaction, N-methylolacrylamide and any organic solvent that dissolves acrylamide can be used. In particular, linear copolymers with extremely high molecular weights can be obtained by polymerization using water as a solvent.

N-methylolacrylamide or acrylamide can be copolymerized with various throatyl monomers. For example, to obtain a linear polymer with a higher molecular weight, methacrylamide, 2-acrylamide-λ-methylpropanesulfonate, etc. may be used.

In particular, N-methylolacrylamide 4cO~yr,s
Morti, acrylamide 1 l 52.5 sulfonic acid o.
Copolymers comprising s Siomolch are useful as anionic flocculants for wastewater treatment containing fine mineral particles.

When polymerizing in an aqueous solution, the concentration of N-methylolacrylamide or a mixture of N-methylolacrylamide and the monomer to be copolymerized is usually within the range of 5% by weight to a saturated solution.

The pH of the monomer aqueous solution is adjusted to 6 using a buffer solution in the neutral range.
It is preferable to adjust it to ~t. This is because, according to the findings of the present inventors, the N-methylol acrylamide and acrylamide copolymer that is the object of the present invention contains formaldehyde remaining from the methylolation reaction, and this is not possible under neutral conditions. Cann1ffZarO below
A reaction occurs to form formic acid, and the formic acid causes a crosslinking reaction in the resulting copolymer. However, such a crosslinking reaction can be effectively prevented by the presence of a buffer.

A common radical polymerization initiator is used as the polymerization initiator. For example, oil-soluble azo compounds, water-soluble azo compounds, hydrogen peroxide, persulfates, perchlorates, hydroperoxides, dialkyl peroxides, ketone peroxides, alkyl peresters, peroxydicarbonates, etc. are used. It will be done.

The amount of the polymerization initiator used is N-methylolacrylamide, and the amount is 0.00 based on the amount of the mixture of N-methylolacrylamide and other highly polymerizable monomers! -1'j
ii. preferably o. o o z~・O0! heavy tits
selected within the range.

The polymerization temperature is selected from the range of 10 to 0°C, preferably from 30 to 70°C.

The polymerization method can be carried out using any reaction apparatus according to various conventionally known methods.

For example, in aqueous solution polymerization, methods include polymerization under stirring, adiabatic polymerization in a static container, polymerization while removing heat in sheet form, polymerization in oil-in-water emulsion, water-in-oil emulsion or dispersion. There are methods such as polymerization in the state.

As for the method of polymerization under stirring, nitrogen gas is passed through a mixed aqueous solution of N-methylolacrylamide and acrylamide to remove oxygen, the temperature is brought to a specified temperature, a radical polymerization initiator is added, and the temperature is maintained at a specified temperature under a nitrogen gas stream. An example of how to do this is given below.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 Ito≠Tulo flask equipped with a stirrer, cooling tube, and thermometer! O weight of acrylamide aqueous solution at 632,7 f
(44.7 mol) and o. tt. 'yd and immersed in a constant temperature water bath at 30°C. The pH inside the container was /I,t.

! A 37% by weight formaldehyde aqueous solution was added to an OO- beaker at j/0. After stirring, the formic acid was neutralized with an aqueous solution of IJ and adjusted to p)l 7 . The sodium hydroxide aqueous solution required for neutralization was 10 3 - and contained u/, 6 ppm formic acid based on the weight of formaldehyde.

Inside the flask / J! The formaldehyde aqueous solution that had undergone the above neutralization treatment was added dropwise over about 10 minutes using a dropping funnel while stirring at speeds of r, p, m.

The pH within the reaction system became 2.7. As the mixture was added, heat generation of approximately λ°C was observed.

After reacting at 30°C for a long time, the production rate of 9N-methylolacrylamide was measured by liquid chromatography.
, 4 mo1%, and the content weight of N,N'-methylenebisacrylamide is 0.4 mo1% based on the weight of the monomer. /
It was less than ppm.

Also, residual formaldehyde was measured.

tA for the charged acrylamide monomer, 7 mob
-, the selectivity of formaldehyde to N-methylolacrylamide was ≠ 6 qb.

This reaction solution was neutralized with M/10 sodium dihydrogen phosphate and transferred to a sealed tube of i'y, rft-rortt with demineralized water.
, 7! t, 1 weight as a polymerization catalyst -〇N, 0.I of an aqueous solution of -azobis-(2-amidinopropane) dihydrochloride
T! Adding f, the total amount was 309.

After replacing the inside of the sealed tube with nitrogen gas and sealing it! When polymerized for μ hours in a constant temperature water bath at 0°C, 2! A water-soluble gel (N-methylolacrylamide-acrylamide Shio-0 copolymer) with a weight percent of water was obtained. Polymerization rate is knotweed, 1%
λ! The reduced viscosity measured using an Ostwald viscometer at °C was ηap10 = /4c, r.

Example The monomer mixture obtained in Example 1 was neutralized with M/10 sodium dihydrogen phosphate, and then placed in a sealed jo-tube.
F), 2.76 f of co-acrylamide-co-methylpropane sulfonate sodium aqueous solution
and demineralized water/0. ! When polymerization was carried out in the same manner as in Example 1 except that f was added, 2! Obtained a water-soluble gel of wt% fF
-(H-menodium = 7 hiro: koλ: hiromol this copolymer).

The polymerization rate was 3%, and the reduced viscosity measured in the same manner as in Example 1 was η5p10 = /! , was 0.

Comparative Example/A reaction solution of acrylamide and formaldehyde was obtained in the same manner as in Example 1 except that 37% by weight of unneutralized formaldehyde was used. The production rate of N-methylolacrylamide in this solution measured by liquid chromatography was 71.7 mob%, and N,N'-
The content weight of methylenebisacrylamide was ≠/ppm relative to the weight of the amide group-containing monomer. The residual formaldehyde was 7 mol % based on the charged acrylamide monomer, and the selectivity of formaldehyde to N-methylolacrylamide was 4%.

When the mixture was combined using a tube, the resulting hydrogel was insoluble in water.

Comparative Examples 2 and 3 1 ppm of N per amide group-containing monomer,
Commercially available N containing N'-methylenebisacrylamide
- Methylolacrylamide aqueous solution (600 weight) and containing λJ ppm of N,N'-methylenebisacrylamide based on the weight of N-methylolacrylamide monomer.The resulting hydrogels were insoluble in water. there were.

〔Effect of the invention〕

According to the method for producing an N-meteroacrylamide-acrylamide copolymer of the present invention, a highly stable and extremely high molecular weight copolymer can be obtained, which contributes to fields of application such as water-soluble or hydrophilic polymers. It is important to do so.

Sender: Mitsubishi Chemical Industries, Ltd. Representative: Patent Attorney Hase - 1 other person

Claims (3)

[Claims] (1) Characteristic in that formaldehyde, which does not substantially contain formic acid, and acrylamide are brought into contact with each other under basic conditions to form N-methylolacrylamide, and then an acid is added to the reaction system to neutralize it, followed by polymerization. A method for producing an N-methylolacrylamide-acrylamide copolymer. (2) A method for producing a copolymer according to claim 1, wherein the copolymer is water-soluble. (3) A method for producing a copolymer according to claim 1 or 2, characterized in that the polymerization is carried out in a buffer solution in a neutral range.