RU2537401C1 - Method of obtaining gel of (co) - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of obtaining gel of (co)polymers of acrylic acid and acrylamide is realised by polymerisation or copolymerisation of monomers, initiated by free radicals and carried out in water medium, as source of free radicals used is monomer pair acrylic acid-acrylamide, reaction of (co)polymerisation and further spontaneous gel-formation of obtained (co)polymers after exhaustion of monomer(s) is provided by preliminary removal of oxygen. Oxygen is removed by vacuuming, or blowing with inert gas, or heating to 100°C with further blowing with inert gas. Initial weight ratio acrylic acid/acrylamide constitutes 5-0.2, total initial concentration of monomers constitutes 0.5-6.0 mol/l. Temperature of (co)polymerisation and further gel-formation is selected in the interval 10-70°C.

EFFECT: simplification of polymerisation method realisation.

4 cl, 4 ex

Description

The invention relates to the field of gel synthesis based on (co) polymers of acrylic acid and acrylamide and can be used to produce water-swellable hydrogels (superabsorbents), flocculants, detergents, as a basis for creating new dosage forms, various composites and material for primitive separation membranes.

It is known to produce poly (meth) acrylic acid or its polymer salts by free radical polymerization of the corresponding monomers (Brief Chemical Encyclopedia. Publishing House "Soviet Encyclopedia", Moscow, 1965, p. 119. Encyclopedia of Polymers. Publishing House "Soviet Encyclopedia", Moscow 1972, volume 1, pp. 36-40. Eizo Qhmori. Acrylic Acid and its Polymer, volume 1, 1973). The process is carried out in an aqueous or organic water-borne medium using radical-forming initiators in a wide range of temperatures, monomer concentrations (see, for example, Polymer, Vol. 46, issue 13 17 Yune 2005. h. 4525-4532) and in the presence of various additives. The purpose of the additives is to increase the ionic strength of the solution, establish the optimal pH of the medium, regulate the molecular weight, crosslink or functionalize the polymer chains, temporarily inhibit the polymerization or, vice versa, make it sensitive to light, lower the residual monomer concentration at the end of the polymerization, serve as a dispersant, etc.

All these processes are united by the need to introduce radical-forming initiators (usually hydrogen peroxide, potassium or ammonium persulfates, organic hydroperoxides, azoisobutyric acid dinitrile), generating free radicals independently, under the influence of temperature or in the presence of various kinds of reducing agents, which contribute to lowering the polymerization temperature (ascorbic acid, sulfites , metabisulfites, thiosulfates and other sulfur compounds with a lower than maximum oxidation state).

The polymerization of acrylic acid and acrylamide is also characterized by the use of photosensitized initiation in the visible or ultraviolet range with the use of additives that readily decay to free radicals under the influence of a quantum of light (see, for example, WO 0006613 A1, 2000-02-10, Polymer, Vol. 50, issue 13, 19 June, p. 2762-2767). Similarly, combinations are known with agents that form free radicals under the influence of γ-radiation (US Pat. US No. 3948740, April 1976).

The thermal initiation characteristic of another type of vinyl monomers, for example styrene, is not effective in the case of acrylic acid and acrylamide and is rarely used due to poorly controlled reaction progress.

The polymerization of acrylamide or its copolymerization with (meth) acrylic acid is also initiated, under the action of the same agents as in the case of acrylic acids, and has no special differences compared to it.

The polymerization of acrylic acid and acrylamide is also characterized by high sensitivity to various kinds of inhibitors, in particular to molecular oxygen, the concentration of which for the normal development of the process should be sufficiently low (for example, according to US Pat. No. 6927268, not higher than 0.5 ppm). In accordance with this, in the case of specially introduced inhibitors, aerobic agents that work only in the presence of oxygen in the system (hydroquinone, benzoquinone, phenol) or anaerobic agents (phenothiazine, US Pat. No. 5,985,958) are used to prevent undesired polymerisation of the monomer during its cleaning, storage, or in other conditions requiring a lack of oxygen.

To obtain water-swellable hydrogels (water sorbents), additives of crosslinking agents having two independently working acrylate-type bonds are used. The most characteristic crosslinkers are methylene-bis-acrylamide, polyoxyethylene glycol diacrylates, multifunctional hydroxyl-containing compounds acrylates, diallyl derivatives of ammonium salts. The amount of crosslinker introduced is selected depending on the desired degree of swelling of the resulting polymer hydrogel and can range from 0.001 to 5% of the monomer (US Pat. No. 7285614).

In the polymerization of acrylic acid, nitrogen-containing additives, in particular with amide functional groups, play an important role. Patents that use compounds of this type can be qualified as patents-analogues of this invention.

A large group of patents for the copolymerization of acrylic acids with nitrogen-containing acrylamide and its derivatives includes the initiation under the action of specially introduced initiators and does not imply the use of one or another comonomer simultaneously as the initiator of the polymerization of the second or their joint polymerization. The most characteristic examples of US Pat. US No. 5297740, No. 5241011.

It is known to graph acrylic acid to many polymer objects and, in particular, to polyamide (6,6) in order to increase the hydrophilicity of polyamide fibers. The best grafting results were obtained with an acrylic acid concentration of 0.5 M, a benzoyl peroxide content of 0.03 M, and a reaction temperature of 85 ° C, i.e. an essential component of the process, as in (co) polymerization, is peroxide (Applied Surface Science. Vol. 253, issue 12, 15 April, 2007, p. 5521-5528).

In patents that use ammonia or aliphatic amines to neutralize acrylic acids, in order to increase the ionic strength of the polymerized solution, “forced” initiation is also applied using the well-known initiating systems of the pure peroxide or redox type. Nitrogen-containing additives do not play the role of independent polymerization initiators, but they can noticeably activate the peroxide initiator, which allows its concentration to be reduced to very low values. A typical example is Pat. US No. 6867269, in which the polyethylene polyamine neutralized with acrylic acid is simultaneously used as a co-initiator and salt-forming crosslinking agent.

Quaternary ammonium salts of (meth) acrylic acids can also serve as comonomers in the polymerization of acrylates in an aqueous medium and also dispersants that lower the viscosity of polymer solutions. For example, (meth) acryloyloxyethylammonium chloride, copolymerizing with a mixture of acrylic acid and acrylamide under the action of a radical-forming initiator such as dinitrile azoisobutyric acid, partially precipitates the initially homogeneous system, converting it into a dispersion with an optimal particle size (US Pat. No. 7,250,462).

In US Pat. US No. 6600819, No. 6552141 to reduce the residual concentration of water-soluble acrylate monomers used ammonium salts of mineral or organic acids in an amount of 5-20% of the monomer. In their presence, at the end of the polymerization, the temperature is raised to 160 ° C and held for 1-1.5 hours. A polymer is obtained with a residual monomer concentration of 10 ppm in the case of acrylic acid and 5 ppm in the case of acrylamide. The initiating group contains potassium persulfate in combination with a photoinitiator. Amine and amide-containing unsaturated compounds were also used as comonomers: N, N-substituted acrylamide, vinyl pyrrolidone, vinyl pyridine. In all cases, the polymerization is carried out under the action of a specially introduced initiator and nitrogen-containing additives play the role exclusively of reducing the residual monomer concentrations.

In US Pat. US No. 7138472, No. 6527959 to obtain a high molecular weight salt of acrylic acid containing an acrylamide additive with a salicylate substituent, polymerization is carried out in reverse emulsion water in oil, in anoxic conditions using sufficiently low initiator concentrations (about 0.1% of the monomer mixture). Salicylamide inserts allowed to improve the properties of the obtained polymer as a flocculant in the Bayer process for the extraction of bauxite. As in the other examples, the nitrogen-containing monomer does not perform an initiating function.

Complex nitrogen-containing compounds having a sufficiently developed π-conjugation system can initiate the polymerization of acrylate monomers in an aqueous medium. In this case, the presence of a strictly fixed oxygen content in the system and its irradiation with light in the absorption band of the selected nitrogen-containing compound are a prerequisite. As an example, polymerization of acrylic acid and acrylamide under the action of water-soluble porphyrins (US Pat. RF No. 2313539). The process is carried out at a low concentration of the photosensitizer, room temperature and a molar ratio of porphyrin / oxygen of 1: 20-30. Get water-soluble polymers with controlled molecular weight or water-swelling hydrogels with a controlled degree of swelling.

Thus, all of the above examples show that the use of nitrogen-containing additives and, in particular, compounds containing amide groups in the polymerization of acrylic acid, provides for a variety of their functions, except initiating.

The initiating activity in the polymerization of acrylate monomers is known for binary systems: carboxylic acid (or its acid chloride) - a tertiary conjugate weakly basic aromatic amine forming a charge-transfer complex (CTC), capable under certain conditions of dissociating into polymerization-active particles (B.A. Dolgoplosk, EI Tinyakova, Generation of free radicals and their reactions, Moscow, Nauka, 1982, 172-174, B. A. Dolgoplosk, EI Tinyakova, Redox systems as sources of free radicals, Mos kva, ed.Nauka, 1972, pp. 190-194). In this case, the polymerization is carried out without the use of peroxide or redox initiators.

These binary systems are characterized by a rather strong donor – acceptor interaction, have a characteristic absorption band at 470 nm, and initiate the polymerization of methyl methacrylate, accelerated by the action of light or in the presence of small oxygen additives. However, there are a number of systems with a relatively weak interaction and, nevertheless, forming a bullpen, which is capable of generating particles active in vinyl polymerization. Numerous complexes of maleic anhydride with various monomers of not only acrylate type, for example, styrene, vinyl butyl ether, n-dioxene, 1,2-dimethoxyethylene, etc., are referred to such systems. (A.N. Pravednikov, S.N. Novikov. Naval Forces, series A, vol. 13, 1971, p. 1404-1413).

Known systems of spontaneous copolymerization involving acrylic acid or acrylamide, which also do not require special introduction of peroxide initiator. In this case, an initiation mechanism is proposed, according to which additive copolymerization proceeds through the formation of zwitterions from nucleophilic monomers (cyclic imino esters, Schiff bases, cyclic phosphonites, etc.) or electrophilic type (lactones, cyclic anhydrides, sulfones, acrylic acid , acrylamide, beta-hydroxyethyl acrylates), (Takeo Saegusa. Pure & Appl. Chem. Vol. 48, pp. 307-315, 1976).

In a later publication (Topics in Current Chemistry, 1982, Vol. 100, New Trends in Chemistry, p. 75-95), the same author presented a list of the most characteristic types of electrophilic and nucleophilic reactivity monomers in which both acrylic acid and acrylamide are qualified as electrophilic reagents, from which it followed that the combination of these monomers cannot lead to the formation of polymerization-active particles (zwitterions according to the authors or the bullpen according to other versions).

Considering the fact that the amidation of carboxylic acids does not always lead to their complete neutralization and the resulting acid amides can be characterized by slightly acidic or weakly basic (amphoteric) properties, we suggested that, by analogy with the carboxylic acid - (weakly basic) system amine, the carboxylic acid - amide system also can form a bullpen that generates active particles that can cause the polymerization of sufficiently active and, in particular, acrylate water-soluble monomers (acrylic acid, acrylamide). In this case, when selecting polymerization conditions and carefully removing inhibitors (molecular oxygen) from the system, polymerization can be carried out without the use of specially introduced peroxide initiators. The initiating function can be performed by the polymerizing (or copolymerizing) pair of monomers itself.

The scope of the proposed idea can be expanded by assuming that to implement the function that initiates the polymerization of the binary carboxyl - urea system, it is absolutely not necessary that both components have a conjugation with an unsaturated bond, i.e. would be acrylate type monomers. In this case, the range of options for initiating the polymerization of acrylic acids or their amides is significantly expanded, i.e. combinations of functions such as polymerization-capable carboxyl amide or polymerization-capable amide-carboxyl become possible.

Examples of such combinations, including various functions and leading to the spontaneous polymerization of acrylic acid or acrylamide, are available in the literature:

- Copolymerization of acrylic and methacrylic acids with N-vinylpyrrolidone. A. Chapiro, Le Doan Trung. European Polymer Journal, Vol. 10, issue 11, nov. 1974, p. 1103-1106.

- Spontaneous polymerization of acrylic acid with 4-vinylpyridine. Seizo Masuda et al. European Polymer Journal, Vol. 37, issue 4, apr. 2001, p. 705-710.

- Polymerization and copolymerization in associated monomeric aggregates. A. Chapiro. European Polymer Journal, Vol. 9, issue 5, May 1973, p. 417-427.

- Spontaneous polymerization of (meth) acrylamides in concentrated aqueous solutions. O.A. Kazantsev, K.V. Shirshin. Polymer, Vol. 45, issue 15, july 2004, p. 5021-5029.

- Spontaneous copolymerization of 2-acrylamido-2-metipropanesulfonic acid with acrylamide and acrylonitrile in concentrated aqueous solutions. A.P. Sivokhin et al. Russian J. of Applied Chemistry, Vol. 80, No. 8, 2007, p. 1394-1399,

- The effect of the structure of (meth) acrylamides on their spontaneous polymerization in concentrated aqueous solutions.

O.A. Kazantsev, A.V. Igolkin, K.V. Shirshin, S.A. Kazakov, N.A. Kuznetsova, A.P. Malyshev. Russian J. of Applied Chemistry, Vol. 76, No. 7, 2003, p. 1112-1117.

- Spontaneous polymerization of 2-acrylamido-2-methylpropanesulfonic acid in acidic aqueous solutions. O.A. Kazantsev, A.V. Igolkin et al. Russian J. of Applied Chemistry, Vol. 75, No. 3, 2002, p. 465-469. Vol. 83, no. 11, 2010, p. 2041-2042.

- The method of anionic polymerization of acrylic and methacrylic acids, as well as acrylonitrile and methacrylonitrile using a resonantly stabilized anion.

Pat. US No. 5494983 dated February 27, 1996.

However, we did not find any references to the possibility of spontaneous (co) polymerization activity of the simplest pair of monomers acrylic acid - acrylamide in the scientific or patent literature. In our opinion, this situation is due to the insufficient attention of researchers to the purity of the system and, in particular, to the presence in it of a powerful inhibitor of this type of polymerization initiation, molecular oxygen. Careful degassing of the system leads to its activation and a sufficiently high speed of the copolymerization process even at room temperature.

Another aspect of the proposed technical solution is to obtain water-swellable gels (hydrogels, superabsorbents). As already noted above, for this, bi- or polyfunctional low molecular weight or oligomeric compounds having copolymerization-active groups at the ends, in most cases of the acrylate type, are usually introduced into the polymerizable system. In this case, the crosslinking of the chains and their loss of solubility occurs during the polymerization process. A water-swollen gel arises, the degree of swelling of which is regulated by the amount of crosslinker introduced.

We found that gelation in the aqueous system polyacrylic acid - polyacrylamide (PAA-PAA) can also, like polymerization, be carried out spontaneously, without the introduction of specially selected crosslinkers. To realize this possibility, it is necessary to exhaust the monomers at the end of their (co) polymerization and the absence of oxygen, as well as in the case of polymerization inhibiting this process. Moreover, the method of producing prepolymers (or copolymers) may be different. It can be carried out independently using radical-forming initiators or prior spontaneous initiation, in accordance with the proposed technical solution. In this embodiment, the gelation process can be considered as a logical continuation of spontaneous (co) polymerization. The type of gel resulting from this is very characteristic; it is described in US Pat. No. 4,647,617 (March 1987) and is characterized as a "popcorn-like material."

The spontaneously generated “popcorn-like” PAK-PAA gel obtained in accordance with the proposed technical solution is stable in time and has a controlled degree of swelling depending on the accepted conditions, which indicates the covalent nature of the cross-links forming it. The most likely direction of the gelation reaction is secondary amide substitution at nitrogen, accompanied by the appearance of imide bonds in the joint PAA-PAA gel. The type of active particles (radical or ionic in nature) that accompany this process is not yet clear, but the intermediate macromolecular complex between PAA and PAA has been described in the literature (European Polymer Journal, Vol. 39, issue 9, September 2003, p. 1867-1874 ) Its formation was recorded by the methods of viscometry, potentiometry, and fluorescence techniques on the example of aqueous solutions of poly-N, N-diethylacrylamide (RDEA) and polyacrylic acid (PAA). With varying ratios of RAA / RDEA, the behavior of the complex depends on the pH of the medium, component concentrations, and temperature. The influence of molecular oxygen on the formation and behavior of the complex is not reported.

So, the object of the proposed technical solution is the combination of a pair of acrylic acid - acrylamide monomers having a carboxyl and amide substitution at the double bond, generating active centers under oxygen-free conditions, capable of initiating (co) polymerization of this pair in an aqueous medium, i.e. to realize at moderate temperatures a spontaneous polymerization process without the participation of any third components and leading, upon its completion, depending on the selected conditions (residual oxygen content and component ratio), to a water-soluble (co) polymer or a cross-linked water-swellable hydrogel.

The closest technical solution to the proposed is US patent No. 5296577 dated March 22, 1994, which is adopted as a prototype. This patent claims a method for producing polyacrylamide or its copolymers with acrylic acid, as well as its alkyl substituted analogues, salts or esters. The polymerization process is initiated by water-soluble azo initiators or redox systems taken in the concentration range 0.0001-0.2 wt.% To the sum of monomers and generating free radicals. The polymerization is carried out in the presence of 2-mercaptobenzothiazole, taken in an amount of 0.3-2.0 wt.% To the sum of the monomers to prevent the formation of a water-insoluble gel. The medium used is water, the pH of the medium is 6-13, the total concentration of monomers is 5-70 wt.%. The molecular weight of the resulting polymers reaches very high values (10000000-15000000).

The disadvantage of the prototype is the need to use special water-soluble initiators of the polymerization of acrylate-type monomers together with a chain transmitter to prevent the occurrence of an undesirable water-insoluble fraction (gel), the formation of which occurs simultaneously with the polymerization process. In addition, to implement the process at low temperatures (the claimed temperature range of 5-100 ° C), it is necessary to "feed" azo initiators with a low-temperature redox system.

The proposed technical solution allows a clear separation of the polymerization itself from gelation, does not require the introduction of free radical initiators and chain regulators, as well as special crosslinking agents for the subsequent production of the gel. The indicated possibility of spontaneous initiation of polymerization and spontaneous subsequent gelation is achieved by releasing the system from molecular oxygen, which inhibits both polymerization and gelation, which allows both processes to be carried out sequentially.

Thus, the technical result of the invention is to simplify the polymerization process in comparison with the prototype, because only two components are used, which are both monomers and the initiating system that causes their (co) polymerization, and due to a clear sequential separation of the polymerization and gelation processes, special agents that prevent gelation during polymerization are not required.

To achieve this result, a method is proposed for producing a gel of (co) polymers of acrylic acid and acrylamide by polymerization or copolymerization of monomers initiated by free radicals and carried out in an aqueous medium, while a monomer pair of acrylic acid - acrylamide is used as a source of free radicals, and the flow (co) polymerization and subsequent spontaneous gelation of the obtained (co) polymers after exhaustion of the monomer (s) provide preliminary removal of oxygen:

- oxygen is removed by vacuum, or by flushing with an inert gas, or by heating to 1000 ° C, followed by flushing with an inert gas.

- the initial weight ratio of acrylic acid / acrylamide is 5-0.2, and the total initial concentration of monomers is 0.5-6.0 mol / L.

the temperature of the (co) polymerization and subsequent gelation is selected in the range of 10-70 ° C, preferably in the range of 20-40 ° C.

The invention consists in the following. Prepare aqueous solutions of acrylic acid (previously freed from the inhibitor) and acrylamide at a monomer concentration of 0.5-6.0 mol / L. The resulting solutions are mixed in such a way as to obtain a weight ratio of monomers selected in the range of acrylic acid / acrylamide 5.0-0.2 while maintaining the total concentration of monomers in the above range. The solutions are degassed by vacuum to a residual pressure of water vapor of not more than 10-15 mm RT. Art. (elasticity at room temperature). The copolymerization at room temperature begins immediately and ends within a few hours. At monomer ratios, when the content of the second component is sufficiently small (0.05-0.005), a prepolymerization induction period is observed, the duration of which can be from several hours to one to two days (with a minimum content of the second component). It is in accordance with the absence of the induction period that the optimal restriction on the content of the second component during polymerization and stable gelation at the end of the polymerization were selected.

In accordance with the above compositions expanded for polymerization, the obtained polymers must be qualified as copolymers when the monomer contents are sufficiently comparable, and as homopolymers when the content of the second component is relatively low and is at the level of the usual dosages of radical-forming (peroxide) initiators. In this case, the second component can be considered as an initiator (or catalyst).

(Co) polymerization can be interrupted at any stage by letting air or oxygen into the system and resuming again after the removal of oxygen. To completely stop the process, gas volumes comparable with the volume of the aqueous phase are required (from 1: 1 to 2-3: 1 depending on the concentration of active centers).

After the monomer (monomers) are exhausted, the process of spontaneous gelation begins, which also occurs only when the vacuum is maintained in the system. The peculiarity of this process is that it does not immediately affect the entire volume and is not accompanied by preliminary gelling. First, the appearance of small white insoluble embryos, which gradually swell, grow and fill the entire water volume, is observed. There is a "pop-root" gel, which was mentioned above. The degree of swelling of the gel thus obtained depends on the initial ratio of monomers. Its formation is more preferable when acrylic acid predominates in the system. The gelation process, as well as polymerization, can be stopped at any stage or not allowed at all after polymerization (a temporary gap between them allows this to happen). This is accomplished by simply letting air or oxygen into the system.

Thus, as follows from the above information, both the polymerization and gelation during the interaction of the amide and carboxyl functional groups of the corresponding acrylate monomers or polymers under oxygen-free conditions are initiated by the same type of active particles, the most likely nature of which is radical. The preceding stage is the formation of a charge transfer complex (CTC), which further dissociates into free radicals.

The most important condition for both (co) polymerization and gelation, as already noted above, is the absence of oxygen in the system, which can be achieved in various ways. The most effective of them is the preliminary degassing of the aqueous phase by evacuation to a minimum residual pressure (the vapor pressure of the water above the solution, usually 10-15 mm Hg) and the cessation of gas bubbles. Inert gas purging is less effective, but it can also lead to the desired results. A sufficiently effective method of deoxygenation by heating monomer solutions to 100 ° C, i.e. to a temperature at which there is a sharp decrease in the solubility of oxygen in water (from 9 mg / l at 20 ° C to 0 at 100 ° C. A quick reference to a chemist. Publishing house "Chemistry", Moscow 1964, p. 313). After this type of degassing, it is necessary to remove the released oxygen from the gas-vapor phase with an inert gas and then isolate the system.

The essence of the proposed technical solution is illustrated by the following examples.

Example 1

The example demonstrates the possibility of initiating the polymerization of acrylic acid and obtaining a gel based on its polymer using a small (catalytic level) acrylamide additive.

13.6 ml of an aqueous solution of acrylic acid of 24% concentration are poured into a 25-ml glass ampoule (concentrated acid is previously freed from the hydroquinone inhibitor by freezing twice at 13 ° C), the content of pure acid is 3.274 g or 45.46 mmol, solution concentration 3 , 34 mol / l. 0.0195 g of acrylamide is added and dissolved there (0.275 mmol, weight ratio of acrylic acid / acrylamide component 167.9). The contents of the ampoule are pumped out with slight cooling to a residual pressure of 13.7 mm Hg. Art. and stopping the release of gas bubbles. The start of polymerization at room temperature (noted by increasing the viscosity of the system) is recorded after 10-15 minutes. After 24 hours, a small sample of the polymer solution is taken into which air is let in. In the solution left under vacuum, 26 hours after the start of polymerization, the appearance of small gel nuclei is noted, which after a few hours increases in volume (swells) and fills the entire volume of the ampoule, absorbing all the available water.

To assess the gelation yield and the degree of swelling of the obtained gel, the selected sample is weighed, placed in water and left at room temperature for 24 hours. Washed from soluble residues and an additionally swollen sample is removed, dried with filter paper, weighed and dried at room temperature to constant weight. The gel yield, counting on the starting acid, was 65.9%, 1 g of washed gel absorbs 13.9 g of water (without taking into account its residual humidity at room temperature and relative humidity of 30%).

In a sample of a polymer solution with a vacuum discharged after polymerization, the gel does not occur for a long time.

A sample of the initial polymer solution, which was not subjected to preliminary evacuation, did not show the presence of even traces of the polymer during aging for a long time (blind experiment, 3 weeks).

In order to eliminate the induction period during polymerization and to shorten the long induction period during gelation, as well as to increase the gel yield, the polymerization is repeated under the above conditions, changing the ratio of acrylic acid / acrylamide monomers to 5.0. Under these conditions, the polymerization begins immediately and ends at room temperature for several hours, after which the formation of a pop-root-like gel begins, the yield of which was 85%.

Example 2

The example illustrates the possibility of initiating the polymerization of acrylamide small (catalytic level) by the addition of acrylic acid.

6.0 g (84.5 mmol) of acrylamide, 0.3 ml of aqueous, acrylic acid solution (concentration of 24% weight) and 17 ml of distilled water are introduced into a 100 ml glass ampoule. Get the weight ratio of the component acrylic acid / acrylamide = 0,0132, the total concentration of monomers of 3.79 mol / L. The resulting homogeneous solution with slight cooling, vacuum to a residual pressure of 12.9 mm RT. Art. and stopping the release of gas bubbles. The start of polymerization at room temperature (noted by increasing the viscosity of the solution) is fixed after 5 minutes. After 48 hours, the homogeneous solution solidifies and becomes non-flowing (rubber-like), no further formation of an insoluble gel is observed, due to the low content of acrylic acid (the polymer does not lose solubility). The yield of the obtained polymer is close to 100%.

, растворитель вода, 25°C. Энциклопедия полимеров. Изд. "Советская энциклопедия", т. 1, стр. 30).A fixed sample of the obtained polymer is dissolved in water and the viscosity is determined using a capillary viscometer, which is 45.5 dl / g (30 ° C), which formally corresponds to a molecular weight of the order of 50 · 10 ⁶ D (according to the formula

, solvent water, 25 ° C. Encyclopedia of Polymers. Ed. "Soviet Encyclopedia", vol. 1, p. 30).

A longer exposure of the polymer solution under vacuum (for 1 month) does not lead to additional changes and the appearance of the gel.

In order to realize the possibility of not only polymerization, but also post-polymerization gelation with an excess of acrylamide with respect to acrylic acid, the polymerization is repeated with an acrylic acid / acrylamide ratio increased to 0.18. Ultimately, after the pop-root-like gel fills the entire water volume, a cross-linked polymer is obtained, which can further swell in water, at least up to 900-1000%.

Example 3

The example illustrates the possibility of spontaneous copolymerization of acrylic acid and acrylamide under oxygen-free conditions, as well as the inhibitory effect of small additives of atmospheric oxygen on subsequent gelation.

2.4 g of acrylamide (33.80 mmol) and 11.0 ml of 24% acrylic acid (2.54 g, 35.33 mmol) are sequentially introduced into a 50 ml glass ampoule. The weight ratio of monomers acrylic acid / acrylamide AK / AA = 1,058. The total concentration of monomers 5.20 mol / L. The contents of the ampoule are subjected to vacuum until the gas bubbles are completely stopped, after which the ampoule is sealed under vacuum. Polymerization at room temperature begins immediately (by increasing viscosity) and continues for 24 hours, after which the ampoule is opened and air is blown, thereby stopping further transformations. Gelation does not occur for a long time. The approximate weight yield of the copolymer (by dry residue after rapid washing of the powder with an aqueous-alcohol solution to remove residual monomers) was 85%. Inherent viscosity 5.2 dl / g (aqueous solution, 25 ° C).

Example 4

The example illustrates the possibility of spontaneous copolymerization of acrylic acid and acrylamide at elevated compared to room temperature.

An aqueous solution of monomers is prepared in a glass ampoule with their molar ratio AK / AA = 1: 1 and a total concentration of 6.1 mol / L. The contents are evacuated in accordance with example 1, and the ampoule is sealed. The temperature is raised yes 65 ° C. The polymerization begins immediately and is characterized by a further rise in temperature, as a result of which, in the absence of proper cooling, it can become uncontrollable. After an hour, the ampoule was opened and the yield of the copolymer (in accordance with Example 3) was determined, which was about 95%.

The polymerization is repeated with a weight ratio of monomers close to unity and their total concentration in aqueous solution equal to 6.0 mol / L. The system is cleaned of oxygen by heating it to 100 ° C and quickly blowing off the vapors released with an inert gas. Polymerization at 70 ° C ends in 1 hour. After cooling to 40 ° C, gelation begins. The obtained cross-linked polymer does not decompose under the action of aqueous solutions of alkalis and increases the degree of swelling in water compared to untreated ones.

Claims (4)

1. A method of producing a gel of (co) polymers of acrylic acid and acrylamide by polymerization or copolymerization of monomers initiated by free radicals and carried out in an aqueous medium, using a monomer pair of acrylic acid - acrylamide as a source of free radicals, and the course of (co) polymerization and subsequent spontaneous gelation of the obtained (co) polymers after exhaustion of the monomer (s) is provided by the preliminary removal of oxygen. 2. The method according to p. 1 characterized in that the oxygen is removed by vacuum, or by purging with an inert gas, or by heating to 100 ° C, followed by purging with an inert gas. 3. The method according to p. 1, characterized in that the initial weight ratio of acrylic acid / acrylamide is 5-0.2, and the total initial concentration of monomers is 0.5-6.0 mol / L. 4. The method according to p. 1, characterized in that the temperature of the (co) polymerization and subsequent gelation is selected in the range of 10-70 ° C, preferably in the range of 20-40 ° C.