Terpolymers of maleic anhydride, scale prevention

Acute shortage of drinking water in some parts of the world is a problem that is seen as seawater. However, its conversion into drinking water by various desalination processes is technically difficult due to the nature of the inorganic salts contained in seawater. Their solubility in water is low and their precipitates may be an obstacle to the mechanism or manner of the desalination process used, examples of the effects of which are clogging of the semipermeable membranes of the osmotic process and deterioration of the distillation process for heat transfer. This lowers the desalination efficiency and eventually causes such a deterioration in performance that the desalination process must be stopped and the equipment cleaned or replaced.

These salt deposits are commonly known as scale, and scale control research has established the use of chemical agents, usually polymers, to control scale deposition, although some have contained surfactants.

The common use of most pesticides is very small. the ratio of the substance to the inorganic salt which needs to be included in the mixture and which slows down the precipitation. Thus, it can be concluded that the control effect is caused by the formation of a complex at the growth site of the slurry that rejects the incoming nuclei, and not by the chelation of inorganic cations of the salt.

The most common polymers selected for use as scale inhibitors are polymethacrylic acid, polyacrylic acid and polymaleic acid and their copolymers with monomers such as acrylamide and vinyl acetate. Some very recently developed scale control polymers include hydrolyzed polymaleic anhydride (U.S. Patent 3,810,834), maleic anhydride-vinyl acetate copolymer (U.S. Patent 3,715,307); a hydrolyzed copolymer of maleic anhydride and a monoethylene unsaturated monomer or mixtures thereof (GB Patent 1,414,918); maleic acid copolymers and terpolymers (NL patent application 7,506,874); acrylic acid polymers (U.S. Patent 3,514,376); methacrylic acid polymer (U.S. Patent 3,444,054); maleic acid copolymers (U.S. Patent 3,617,577); styrene-maleic anhydride copolymers (U.S. Patent 3,289,734); and polyacrylic acid (U.S. Patent 3,293,152).

A comparison of the nature of the polymer and the anti-scale activity of the scale, as described in the prior art above, suggests that reducing the molar ratio of the maleic anhydride moiety to other monomer moieties in the copolymers or terpolymers thus composed reduces both the bulk density and the pottery density. For example, the scale control results reported for the polymers in GB 1,414,918 reveal that the activity against calcium carbonate precipitation decreases as one proceeds through the series of activities associated with maleic anhydride homopolymer via maleic anhydride diacrylamide ethylhydride acid maleic copolymer of maleic anhydride diacrylamide. The same trend is evident from a comparison of the anti-scale activities of the polymers in NL patent application 7,506,874. When the ratio of the maleic anhydride moiety to the rest of the monomer moiety in the test polymer formed according to this application is reduced, the activity against the precipitation of calcium carbonate decreases. Thus, the literature teaches that the use of non-carboxylic acid monomers in conjunction with a maleic anhydride monomer to form a mixed composition polymer causes the a decrease in the anti-scale activity of the polymer relative to the hydrolyzed polymaleic anhydride.

As with most polymers, the method used to make the scale control polymer affects its nature and activity, regardless of the interrelationships of the monomers used. General methods for preparing scale control polymers are described in U.S. Patent Nos. 3,755,264 and 3,359,246, in addition to the methods included in the aforementioned use patents. Although this prior art provides a wealth of information on how to prepare maleic anhydride and / or acrylic acid polymers, in practice these methods often result in uncontrolled polymerization rates, Tromsdorff effect, prolonged gelation and rubberization of polymers during polymerization, failure of polymerization and failure of polymer molecules. unreliable nature.

In view of previous manufacturing methods and activity suggestions in the art, it is surprising to find that the interaction of monomer composition temperature and reaction solvent in accordance with this invention allows the preparation of a novel granular maleic anhydride terpolymer having a controlled molecular weight range and a low maleic anhydride content. but which nevertheless has approximately the same scale control activity as hydrolyzed polymaleic anhydride.

This new process can also be used to make useful maleic anhydride copolymers that are granular and easy to handle.

The invention thus relates to a process for the preparation of a terpolymer consisting of 30 to 55 mol% of maleic anhydride, 30 to 65 mol% of acrylamide or methacrylamide and 5 to 15 mol% of a third monomer, which third monomer is selected from: Styrene, CA-methylstyrene and 1-alkene having 4 to 10 carbon atoms and having a terpolymer viscosity ratio in dimethyl sulfoxide of 0.5 g / dl of about 1.02 to 1.10 and a solubility in water at room temperature of less than 0.10 g / g of solution.

The process according to the invention is characterized in that a mixture of maleic anhydride and acrylamide or methacrylamide is heated to at least 120 ° C in a chain transfer solvent mixture, 2-20% by weight of free radical initiator and a third monomer are added to the mixture and the mixture is further heated to at least 120 ° C substantially complete, and that the chain transfer solvent contains 15 to 85% by weight of an aromatic solvent, namely dialkyl-substituted benzene, having 1 to 4 carbon atoms in each alkyl group, and 15 to 85% by weight of a ketone, namely a dialkyl ketone having 1 to 5 carbon atoms in each alkyl group.

Preferably, the terpolymers prepared according to the invention have a solubility in water of less than 0.06 g / g of solution.

A terpolymer composition in which the monomer is styrene is preferred due to the preferred balance of scale action and hydrophobicity of its hydrolyzed form. The preferred monomer ratio of this terpolymer is 30-50 mol% maleic anhydride, 50-55 mol% acrylamide and 5-15 mol% styrene. A monomer ratio of 41 to 45 mol% of maleic anhydride, 45 to 49 mol% of acrylamide and 9 to 13 mol% of styrene are particularly preferred. The preferred copolymer composition is a copolymer of 45-55 mole% maleic anhydride and 45-55 mole% acrylamide.

The terpolymers and copolymers prepared by the process of the invention can be isolated as a granular precipitate and not as a rubber, resin or oil, and are therefore sparingly soluble in water at ambient temperature. This low solubility is believed to be due to a rearrangement of the chemical structure of the polymer; in any case, the sparing solubility is clearly dependent on the temperature and solvent of the reaction process. Most likely, the process works by forming a significant number of imide groups along the polymer backbone by causing the anhydride portion of the maleic anhydride fragment to recombine with the amide portion of the acrylamide fragments. According to the theory, imide groups then in turn cause the observed low solubility. The low solubility is further increased by the hydrophobicity of the third monomer of the terpolymer.

In order to achieve the desired low solubility in water at ambient temperature and the formation of a granular precipitate, it is necessary to use reaction temperatures of at least 120 ° C and chain transfer solvents or mixtures thereof which tend to separate free radicals and have higher polarity than toluene involved in the polymerization chain reaction. The solvent must also not affect the swelling or agglomeration of the polymer granules formed.

The sparing solubility of the polymer in water can be utilized for purification. Slurrying the crude reaction polymer in cold water dissolves the water-soluble monomers, leaving the polymer substantially free of unreacted monomer. In this way, possible contamination of the desalination process with residual monomer is avoided.

The compounds of this invention have unexpected characteristics that are thought to be due to the significant number of imide groups along the polymer backbone and the hydrophobic effect of the third monomer. An essential part of the assumption is that the imide groups along the polymer chain as five- and six-membered rings and bridges across the polymer chains are generated by the process of this invention by regrouping the anhydride and amide portions of the polymer as the polymer is formed.

The sparing solubility of terpolymers in water at ambient temperature can also be created as a property of the maleic anhydride-acrylamide copolymers prepared by the process according to the invention. The observation of this phenomenon in the copolymer supports the idea that the sparing solubility of both types of polymer of the present invention is mainly due to the presence of imide groups and that the hydrophobicity of the third monomer in the terpolymer reinforces this effect.

In order to achieve the desired transformation in the polymerization, the following reaction parameters must be taken into account: similar molar amounts of anhydride and acrylamide monomers, temperature, solvent and method of addition of the third monomer of the terpolymer. These are critical to the success of the end result and provide the necessary conditions to achieve the desired low solubility.

The temperature in the reaction must be at least 120 ° C, and when using solvents boiling at a lower temperature under normal pressure, this can be achieved by using pressure. The upper limit of the temperature range depends on the controllability of the reaction rate and the reflux temperature of the solvent or solvent mixture, provided that the solvent or mixture used boils above 120 ° C. The recommended temperature used is the solvent reflux temperature, which is usually 125-150 ° C.

The reaction time parameter varies depending on the starting materials used in each case. The progress of the polymerization can be monitored by observing the precipitation of the polymer into fine particulate granules and the polymerization is substantially complete when the precipitation ceases. The total reaction time is usually 1 to 10 hours, most often about 2 hours.

The reaction solvents used in the process of this invention are reactive; that is, they are involved in the chain growth and termination stages of polymerization. Suitable solvents include dialkyl substituted benzenes such as toluene and aliphatic ketones such as methyl ethyl ketone, acetone, 4-methyl-2-pentanone, di-butyl ketone and dipropyl ketone. The process uses a mixture of aromatic and ketone solvent in a ratio of 15 to 85% by weight of ketone solvent to 15 to 85% by weight of aromatic solvent. In each case, the relative amounts selected depend on the nature of the polymer to be formed. But in general, these ratios ensure that the polymer does not agglomerate or swell during its formation.

The preferred chain transfer solvent mixture contains substantially equal amounts of xylene and methyl isobutyl ketone.

Any free radical initiator capable of initiating a free radical reaction can be used in the process. Typical initiators are di-t-butyl peroxide, benzoyl peroxide, azobisisobutyronitrile, dicumyl peroxide and dilauroyl peroxide. Although the weight ratio of initiator to monomer varies according to the monomers used in each case, the range is usually 2 to 20% by weight based on the total amount of monomers.

According to these reaction parameters, the terpolymer of the present invention is formed by first contacting 30-55 mol% of maleic anhydride with 30-65 mol% of acrylamide or methacrylamide in a suitable reaction solvent. The mixture is heated to a suitable temperature and the free radical initiator and 5-15 mol% of the third monomer described above, both dissolved in the reaction solvent, are then added to the reaction mixture preferably at such a rate that the addition is completed in 15-180 minutes. At the usual rate of addition, the period is approximately 30-60 minutes.

To form the copolymer of this invention, 30 to 70 mole percent maleic anhydride is contacted with 30 to 70 mole percent acrylamide or methacrylamide in the same manner as was shown for terpolymers except that the third monomer is omitted.

The reaction is preferably carried out in an inert atmosphere, for example nitrogen.

The reaction mixture is preferably stirred throughout the reaction, for example by stirring or introducing an inert gas into the mixture.

Isolation of the polymer can be accomplished by any standard technique known and available in the art. The usual method is to concentrate the reaction medium by evaporating, filtering and then slurrying the filtered solids in cold water to dissolve the unreacted monomer. This produces a polymer that is substantially free of unreacted monomer. Other methods include washing the filtered reaction material with organic solvents such as ether, tetrahydrofuran, chloroform, carbon tetrachloride, and the like, non-polar, hydroxyl-free organic solvents.

The polymer is then hydrolyzed to control the scale by boiling it under reflux in water. The insoluble polymer is converted to a soluble, hydrolyzed polymer usually in 6-10 hours. Alternatively, the polymer can be hydrolyzed by mixing it with an aqueous solution of 0.1-4 molar sodium hydroxide at temperatures between 25-100 ° C.

The alkali metal and ammonium salts of the hydrolyzed terpolymer can be formed by adding an alkali metal base, ammonia, or organic amine to an aqueous solution of the hydrolyzed terpolymer, or by using a base to hydrolyze the non-hydrolyzed terpolymer directly. Evaporation of water isolates the desired terpolymer salt; the salt can also be used in aqueous solution without isolation. Common alkali metal bases include sodium hydroxide, potassium hydroxide and lithium hydroxide. Common ammonium bases and amines include ammonium hydroxide, ammonia, mono-, di-, and trialkylamines having 1 to 5 carbon atoms in each alkyl group, pyridine, morpholine, and lutidine.

The hydrolyzed terpolymers of the invention and the like salts can be used to prevent scale formation by heating water or desalting water containing scale-forming impurities, for example, removing calcium and magnesium ions from seawater, steam boiler water, etc. Solid hydrolyzed terpolymer so that a concentration of at least 2 ppm is obtained in the water. Alternatively, the hydrolyzed terpolymer or a salt thereof may be fed to water containing scale-forming impurities using a concentrated aqueous solution to form a concentration of at least 2 ppm in the water. This treatment can be performed, as will be appreciated by those skilled in the art, in any manner consistent with the processes used to treat the water. Thus, if a batch desalination process is used, the scale pesticide of the invention is fed in batch amounts. On the other hand, if a continuous desalination process is used, the scale remover can be added continuously to a circulating pipeline for water containing scale-forming impurities or added to a source which acts as a compensating vessel for continuous desalination. Scale control in steam boiler applications is achieved in the same way. As will be readily apparent to those skilled in the art, the operation will require interruption from time to time to remove concentrated contaminants which the substance is suspended in a pan or pot. However, the cleaning procedure is usually a simple emptying and rinsing of the pan or pot and not the difficult cleaning required to remove the scale layer.

The characteristic insolubility of the terpolymers and copolymers of this invention in water at ambient temperature is shown in Table 1. It was determined by stirring a 25% by weight mixture of polymer in distilled water at room temperature for 3 hours, followed by removal of the liquid phase. The dissolved polymer was then recovered from the liquid phase by freeze-drying the solution, and both this material and the insoluble polymer were dried at 25 ° C above phosphorus pentoxide under a vacuum of 0.1 torr for approximately two days. The weights of dissolved and insoluble polymer were compared, and the results were expressed in grams of dissolved polymer per gram of solution for that mixture. The polymer of Method A selected for comparison was prepared according to the general method disclosed in GB Patent 1,414,918.

To show that the insolubility is not time dependent, the terpolymer of Example 1 was blended for two days in the same manner and in the same proportions as described above. After stirring for two days at ambient temperature, the polymer was isolated in the same manner as above and had a solubility of 0.0408 g / g of solution.

A comparison of the solubility behavior of the polymers of this invention (Table 1) with the corresponding property of the method A polymer shows that the solubility properties of the polymers of this invention are clearly different from the corresponding property of the method A polymer. This difference is explained when comparing polymer production processes (compare method A to example B). The polymerization temperature is higher in the process of this invention (at least 120 ° C compared to the range of 70-110 ° C in Process A), and a mixture of an aromatic and a ketone solvent is used as the solvent. As a result, the process of the present invention provides suitable conditions for inducing new water to Liu non-lubricity, which is believed to be associated with the formation of imide moieties in co- and terpolymers.

table 1

Insolubility of the polymer

Polymer composition Example Solubility (based on g polymer (mole%, analysis no. Dissolved in g solution))

<td> 49</td><td>maleic anhydride</td><td> 8</td><td> 0,058</td>

<td> 51</td><td>acrylamide</td><td></td><td></td>

<td> 29</td><td>maleic anhydride</td><td> 10</td><td> 0,080</td>

<td> 71</td><td>acrylamide</td><td></td><td></td>

<td> 46</td><td>maleic anhydride</td><td> 9</td><td> 0,073</td>

<td> 54</td><td>methacrylamide</td><td></td><td></td>

<td> 43</td><td>maleic anhydride</td><td> 1</td><td> 0,050</td>

Table 1 continued Polymer insolubility

<td>Polymer composition</td><td>Example</td><td>Solubility (g poly-</td>

<td>(mole%, analysis</td><td>n: o</td><td>mer dissolved in g</td>

<td>by)</td><td></td><td>solution)</td>

<td>46 acrylamide</td><td></td><td></td>

<td>11 styrene</td><td></td><td></td>

<td>58.4 maleic anhydride</td><td>method</td><td>the polymer completely dissolved</td>

<td>41.7 acrylamide</td><td>(A)</td><td></td>

<td>(polymers of Examples 2-7</td><td>solubilities</td><td>were less than 0.05 g / g of solution</td>

ta).

The anti-scale activity of the hydrolyzed terpolymers of this invention was determined by measuring the amount of precipitate formed when heated under pressure a standard solution of synthetic seawater containing a scale inhibitor of the added terpolymer. The procedure and results are shown in Example 1 and must be compared with two types of reference solutions, one in which no substance, and another using polymaleic acid (formed according to the methods disclosed in GB Patent 1,414,918). These results indicate that although the charge density of these hydrolyzed terpolymers has been reduced relative to the corresponding value of polymaleic acid and their hydrophobicity has been increased, the hydrolyzed terpolymer of the present invention has significant anti-scale activity approximately equal to that of polymaleic acid. The hydrolyzed terpolymers of this invention are required to act in the control of scale through a threshold mechanism in which binding of the hydrolyzed terpolymer to the crystal nuclei growth site prevents more crystal growth at this site and the third monomer contained in the bound terpolymer expels the incoming aqueous jacket containing dissolved ions.

The following Examples 1-11 illustrate the invention. (Example A is a comparative example).

All temperatures are in degrees Celsius and unless otherwise specified are ambient temperatures.

Infrared spectra were obtained on a Perkin-Elmer IR-21 lattice spectrophorometer and are reported in micrometers.

Viscosity measurements used to calculate the molecular weight of the polymers were performed by a standard method on an Ubbelohde viscometer using a solution of 0.5 g of polymer in 100 ml of dimethyl sulfoxide at 25-0.01 ° C. The measured viscosity was the relative viscosity (nu), defined by the formula nu = t / to, where t is the flow time of the polymer solution in seconds and to is the flow time of the solvent in seconds.

Method A

Copolymer (A) of maleic anhydride and acrylamide formed in accordance with GB Patent 1,414,918

A solution of 46.5 g (0.474 mol, 71.4 mol%) of maleic anhydride, 13.5 g (0.190 mol, 28.6 mol,%) of acrylamide and 143.0 g of toluene was stirred and heated under nitrogen until a temperature of 70 ° C was reached. To the solution was then added 12.0 g (20% by weight) of benzoyl peroxide in 70.0 g of toluene over 5 minutes. The solution was then refluxed at 11-13 ° C for 6 hours. After cooling, the toluene solution was decanted from the resinous material, which was purified by trituration in benzene. A 63% yield of copolymer A with a relative viscosity of 1.04 was obtained.

Composition of copolymer A as determined by CHN analysis:

58.4 mole% maleic anhydride

41.7 mole% acrylamide

Example 1

Terpolymer of maleic anhydride, acrylamide and styrene (1)

To a 4-necked 200 mL round bottom flask equipped with a reflux condenser and mechanical stirrer was added 150.0 g (1.53 moles, 45 mole%) of maleic anhydride, 108.8 g (1.53 moles, 45 mole%) of acrylamide. , 235.0 g of methyl isobutyl ketone and 235.0 g of xylene. The system was purged with nitrogen and then the flask was lowered into an oil bath maintained at 150 ° C and as the reaction mixture warmed, it formed a solution. When slight reflux was achieved at a reaction mixture temperature of 126-130 ° C, a solution of the free radical initiator containing 14.71 g of di-t-butyl peroxide, 16.0 g of methyl isobutyl ketone and 16.0 g of xylene was added continuously at such a rate. that the addition was completed in 30 minutes. Simultaneously, a solution of the third monomer containing 35.4 g (0.340 mol%) of styrene, 29.0 g of methyl isobutyl ketone and 29.0 g of xylene was added continuously at such a rate that the addition was completed in 60 minutes. During and after the addition of the third monomer, the polymer precipitated as a flowing reaction slurry. After the polymerization was substantially complete, in 2 hours, the polymerization mixture was allowed to cool to room temperature, the mixture was filtered and the precipitate was washed with diethyl ether and dried in a vacuum oven at 80 ° C for 17 hours. Alternatively, the precipitate can be washed with water and dried in a vacuum oven. The resulting brown free-flowing powdered terpolymer 1 was obtained in 87.6% yield and had a relative viscosity of 1.04.

Composition of terpolymer 1 as determined by CHN analysis:

mole% maleic anhydride mole% acrylamide mole% styrene

IR (KBr) 2.94, 3.02, 5.42, 5.64, 5.80, 5.86, 6.06, 6.22 and

8,40.

Other terpolymers of this invention may be prepared according to the procedure of Example 1, substituting the appropriate monomers for the monomers of Example 1.

Example 2

Terpolymer of maleic anhydride, acrylamide and styrene (2)

Terpolymer 2 was prepared according to the procedure of Example 1 using the same molar percentages of monomers, but substituting 75% w / w methyl isobutyl ketone, 25 wt% xylene for the solvent ratio of Example 1. An 87.5% yield of free-flowing powdered terpolymer 2 with a relative viscosity of 1.04 was obtained.

Composition of terpolymer 2 as determined by CHN analysis:

mole% maleic anhydride mole% acrylamide mole% styrene

The IR spectrum (KBr) was identical to that of terpolymer 1.

Example 3

Terpolymer of maleic anhydride, acrylamide and styrene (3)

The terpolymer was prepared according to the procedure of Example 1 by replacing the monomer ratios of Example 1 with 55 mol% maleic anhydride, 35 mol% acrylamide and 10 mol% styrene. A 88.1% yield of free-flowing, granular terpolymer 3 with a relative viscosity of 1.04 was obtained.

Composition of terpolymer 3 as determined by CHN analysis:

50.09 mol% of maleic anhydride

35.5 mole% acrylamide

13.4 mole% styrene.

The IR spectrum (KBr) was identical to that of terpolymer 1.

Example 4

Terpolymer of maleic anhydride, acrylamide and styrene (4)

Terpolymer 4 was prepared according to the procedure of Example 1 using the same monomer ratio, but substituting an equimolar amount of di-t-butyl peroxide for dicymyl peroxide. An 88.2% yield of granular terpolymer 4 with a relative viscosity of 1.039 was obtained.

Composition of terpolymer 4 as determined by CHN analysis:

44.5 mol% of maleic anhydride

44.6 mole% acrylamide

10.9 mol% styrene

The IR spectrum (KBr) was identical to that of terpolymer 1.

Example 5

Terpolymer of maleic anhydride, acrylamide and 1-octene (5)

To the flask were added 183.4 g (1.871 mol, 55 mol%) of maleic anhydride, 72.5 g (1.021 mol, 30 mol%) of acrylamide, 215.0 g of methyl isobutyl ketone and 215.0 g of xylene. The system was purged with nitrogen for 1.5 h and then lowered into an oil bath maintained at 150 ° C. When light reflux was achieved at a reaction mixture temperature of 126-130 ° C, a solution of 31.3 g of dicumyl peroxide, 36.0 g of methyl isobutyl ketone and 36.0 g of xyl65075 len was added dropwise over 1 hour. Simultaneously, a solution containing 57.3 g (0.510 mol, 15 mol%) of 1-octene, 47.0 g of methyl isobutyl ketone and 47.0 g of xylene was added dropwise over 0.5 h. When the polymerization was substantially complete in 4.0 hours, the reaction was allowed to cool. The particulate terpolymer was filtered, washed with excess diethyl ether and dried in a vacuum oven at approximately 90 ° C. A 56% yield of a brown, free-flowing, powdered terpolymer 5 with a relative viscosity of 1.040 was obtained.

Composition of terpolymer 5 as determined by CHN analysis:

50.9 mol% of maleic anhydride

41.2 mole% acrylamide

7.85 mol% of 1-octene

The IR spectrum (KBr) was similar to that of terpolymer 1.

Example 6

Terpolymer of maleic anhydride, methacrylamide and styrene (6)

Terpolymer 6 was prepared according to the procedure of Example 1 by replacing acrylamide with methacrylamide in the same molar ratio. A 95% yield of granular terpolymer 6 with a relative viscosity of 1.053 was obtained.

Terpolymer composition as determined by CHN analysis.

42.8 mol% of maleic anhydride

46.7 mole% methacrylamide

10.3 mole% styrene

Example 7

Terpolymer of maleic anhydride, acrylamide and alpha-methylstyrene (7)

Terpolymer 7 was prepared according to the procedure of Example 1 by replacing styrene with alpha-methylstyrene in the same molar ratio. An 89.4% yield of granular terpolymer 7 with a relative viscosity of 1.046 was obtained.

Composition of terpolymer 7 as determined by CHN analysis:

49.5 mole% maleic anhydride

44.9 mole% acrylamide

10.9 mole% alpha-methylstyrene.

Example 8

Copolymer of maleic anhydride and acrylamide (8)

To a four-necked 2000 ml round-bottomed flask equipped with a mechanical stirrer, N₂150.0 g (1.53 mol, 50 mol%) of maleic anhydride, 108.7 g (1.53 mol, mol%) of acrylamide, 224.0 g of 4-methyl were added via a -2-pentanone and 224.0 g of xylene. The mixture was stirred at room temperature and purged with nitrogen for 15 minutes. The system was then lowered into an oil bath maintained at 130 ° C and at 60 ° C the solid starting materials dissolved. When the solution gently refluxed at 126-130 ° C, a solution of 12.98 g (10% by weight) of di-t-butyl peroxide, 16.0 g of methyl isobutyl ketone and 16 g of xylene was added dropwise over 30 minutes. After the addition of the initiator, precipitation of the polymer occurred. After one hour, a second solution of 12.98 g of di-t-butyl peroxide and 112.5 g of xylene was added dropwise to the polymerization medium over 2 hours. The polymerization was allowed to continue for a further 1 hour, after which the dispersed mixture was cooled to room temperature, the precipitate was filtered, washed with diethyl ether and dried in a vacuum oven at 90 ° C. Alternatively, the precipitate can be washed with water and dried in a vacuum oven. An 89.6% yield of free-flowing powdered copolymer 8 with a relative viscosity of 1.05 was obtained.

Composition of the copolymer as determined by CHN analysis:

mole% maleic anhydride mole% acrylamide

IR spectra (KBr) 2.94, 3.02, 5.43, 5.65, 5.86, 6.02, 6.20 and 8.45.

Other copolymers of this invention can be synthesized according to the procedure of Example 8 by substituting the appropriate monomers and ratios of Example 8 for the appropriate monomers.

Example 9

Copolymer of maleic anhydride and methacrylamide (9)

Copolymer 9 was prepared according to the procedure of Example 6 omitting the styrene monomer. An 85% yield of free-flowing, powdered copolymer 9 with a relative viscosity of 1.05 was obtained.

Composition of the copolymer as determined by CHN analysis:

mole% maleic anhydride mole% methacrylamide

IR spectra 2.96, 3.03, 5.45, 5.65, 5.80, 5.86, 6.02, 6.25 and 8.23.

Example 10

Copolymer of maleic anhydride and acrylamide (10)

Copolymer 10 was prepared according to the procedure of Example 8, substituting the monomer ratios of Example 8 for 25 mol% maleic anhydride and 75 mol% acrylamide. A 96.7% yield of free-flowing, powdered copolymer 10 with a relative viscosity of 1.10 was obtained.

Copolymer composition by CHN analysis:

71.8 mole% acrylamide

28.2 mol% of maleic anhydride.

Example 11

The scale action of the hydrolyzed polymers of Examples 1-10

Synthetic seawater was prepared by dissolving the following weights of inorganic salts in one liter of distilled water:

NaCl, 26.5 g; MgCl 1₂, 2.4 g; MgSC&gt;₄, 3.3 g; CaCl 2₂, 1.1 g; KCl 0.72 g; NaHCO 3, 0.245 g and NaBr, 0.08 g.

To perform the experiment, a 0.1% aqueous solution of 1.0 ml of hydrolyzed polymer was added to a beaker containing 166 ml of synthetic seawater and a 1 square inch multi-metal foil. A test beaker and a positive reference beaker containing 166 ml of seawater, 1.0 ml of a 0.1% aqueous solution of polymaleic acid (prepared according to the method of GB 1 414 918) and a 1 square inch multi-metal foil were placed in an autoclave (pressure cooker) containing stirring lithium chloride 10 % aqueous solution. The autoclave overpressure valve was set to 10 psi so that the boiling point of the seawater sample rose to 115 ° C and the autoclave was sealed and heated until steam began to escape from the overpressure valve (20-30 min.). Heating was continued for 45 min, after which the autoclave was allowed to cool. When the internal pressure of the autoclave dropped to normal pressure, the control and sample decanters were removed and cooled in a 25 ° C water bath. Both beakers were analyzed separately as follows. The multimetal foil was removed and rinsed with 50 mL of 6 N HCl to remove any scale formed. The final volume of seawater was measured and the amount evaporated was calculated. The seawater was filtered through a 0.2 cellulose membrane filter to recover the precipitate formed, and the acid used to wash the monolith was slowly passed through the filter to dissolve the precipitate. The volume of the acid solution was then measured and the amount of precipitated calcium and / or magnesium compounds was measured by EDTA titration of the acid wash fraction. A total of four test samples and four positive controls were run and means and standard deviations were calculated. The mean water lost was also calculated and the standard deviation was searched. It was calculated as a percentage of the total and expressed as a percentage of evaporation. The means of the positive comparisons and their evaporation percentages were compared to the table showing the evaporation percentages against and against the polymaleic acid of the same type and origin as in Table III presented here. The comparison was used to ensure that nothing abnormal had occurred during the experiment.

The average results of the scale control test using the polymer of each of the different examples of this invention are shown in Table II in milliequivalents of EDTA-complexed calcium / magnesium, together with the results obtained from the zero control test (test without any scale control polymer). The evaporation percentage is given in Table II in connection with the average scale result.

In order to compare the anti-scale activity of the test polymers with the activity of the positive reference compound, polymaleic acid, it was necessary to determine what effect the amount of evaporation had on the scale layer. Assuming that the positive reference standard was polymaleic acid and that the evaporation percentage was mainly dependent on equipment and test conditions and not on the type of scale control agent, such an assay was made by repeatedly testing polymaleic acid as scale control agent under the test conditions described above. For the amounts of scale deposition in each experiment that occurred for each 0.6% evaporation increment from 12% evaporation, averages were taken and the standard deviation of each mean was calculated. These averages and their corresponding evaporation ranges are shown in Table III.

Using the data in Table III, the potency of the example polymers as scale inhibitors can be compared to the potency of polymaleic acid. After selecting the increase in Table III with the evaporation percentage range for which the evaporation percentage of the sample polymer in question would occur from Table III, the average scale for this region growth is compared to the average scale in the sample sample. scale value with polymaleic acid, the polymer of the example is a more active scale control agent than polymaleic acid. In considering this comparison, the variance of both the average scale values ​​of the sample and the scale values ​​of the polymaleic acid must be taken into account to judge the benefits of the sample polymers relative to the positive standard, polymaleic acid.

Table II

Anti-scale activity of hydrolyzed exemplary polymers

Example polymer Average sample Average evaporation No. scale value stand, (hydrolyzed poly (m-equiv.) Stand, deviation% deviation sea)

<td> 1</td><td> 0.102</td><td> 0.028</td><td> 15.1</td><td> 1.5</td>

<td> 2*</td><td> 0.158</td><td> 0.039</td><td> 13.6</td><td> 1.8</td>

<td> 3</td><td> 0.080</td><td> 0.008</td><td> 13.0</td><td> 0.6</td>

<td> 4</td><td> 0.079</td><td> 0.028</td><td> 13.6</td><td> 0.6</td>

<td> 5*</td><td> 0.143</td><td> 0.023</td><td> 15.4</td><td> 1.4</td>

<td> 6</td><td> 0.149</td><td> 0.046</td><td> 14.9</td><td> 1.6</td>

<td> 7</td><td> 0.073</td><td> 0.026</td><td> 12.3</td><td> 0.7</td>

<td> 8*</td><td> 0.149</td><td> 0.015</td><td> 15.3</td><td> 1.2</td>

<td> 9</td><td> 0.110</td><td> 0.060</td><td> 15.9</td><td> 1.2</td>

<td> 10</td><td> 0.115</td><td> 0.032</td><td> 15.5</td><td> 2.4</td>

<td>Zero comparison</td><td> 0.200</td><td> 0.005</td><td> 15.0</td><td> 2.4</td>

x) Both the amount of scale in the sample and the amount of scale (polymaleic acid) in the positive control deposited during the test runs in these examples were abnormally high, e.g., in Example 2, the average amount of scale deposited with polymaleic acid during that test was 0.127; in Example 5 it was 0.148 and in Example 8 it was 0.15.

Table III

Scale layer as a function of evaporation percentage using polymaleic acid as scale scavenger

Evaporation Rate- Observed mean standard deviation range of scale (m-equiv.)

<td> 12.0-12.6</td><td> 0.065</td><td> +0.013</td>

<td> 12.6-13.2</td><td> 0.075</td><td> +0.003</td>

<td> 13.2-13.8</td><td> 0.081</td><td> +0.007</td>

<td> 13.8-14.4</td><td> 0.106</td><td> +0.010</td>

<td> 14.4-15.0</td><td> 0.117</td><td> +0.009</td>

<td> 15.0-15.7</td><td> 0.119</td><td> +0.004</td>