Process for preparing water soluble polymers of monoethylenically unsaturated dicarboxylic acids

Abstract: The present invention provides an efficient aqueous polymerization process of 6 hours or less for preparing water soluble polymer products formed from 50 to 100 weight percent of one or more monoethylenically unsaturated dicarboxylic acid monomers and 0 to 50 weight percent of one or more optional other water soluble monoethylenically unsaturated monomers. In this process, 1) an aqueous reaction mixture of dicarboxylic acid monomer is formed, 2) from about 0.9 to about 2.1 equivalent moles of base are added to the reaction mixture per mole dicarboxylic acid monomer, 3) at least one metal promoter is added to the reaction mixture, 4) one or more initiators and optional other water soluble monoethylenically unsaturated monomer are fed to the reaction mixture, 5) the weight percent reaction solids during the polymerization is between about 40 and about 65 weight percent, and 6) the reaction temperature is maintained at about 80 °C to about 140°C. The polymer product produced by the process of the present invention is useful as an additive in detergents, cleaning formulations, and water circulating systems.

Description: This invention relates to an improved aqueous free radical addition polymerization process for preparing water soluble polymers formed from one or more monoethylenically unsaturated dicarboxylic acid monomers and optionally one or more other water soluble monoethylenically unsaturated monomers. In particular, this invention relates to an efficient process which produces a polymer product containing less than 1.5 weight percent unreacted dicarboxylic acid monomer based on the total weight of polymer product and allows for a minimum polymerization reaction time of less than about 3 hours. Water soluble polymers formed from monoethylenically unsaturated dicarboxylic acid monomers, herein called "dicarboxylic acid monomers" and optionally other water soluble monoethylenically unsaturated monomers, herein called "optional other water soluble monomers" are useful as scale inhibitors, deflocculants, dispersants, in water circulating systems and as incrustation inhibitors, builders, anti-filming agents, sequestering agents, and dispersants in detergents and cleaning formulations. Several techniques for preparing these water soluble polymers by free radical addition polymerization in aqueous systems are known. However, a common problem in forming these polymers is that the dicarboxylic acid monomer, such as maleic acid, is slow to react in comparison to the other monomers, such as acrylic acid, in free radical addition polymerizations. To compensate for this slow reactivity of the dicarboxylic acid monomer, one process which has been developed for producing these polymers is described in U.S. 4,659,793 to Yang, herein called "Yang". Yang discloses a process where a "heel" or solution of partially neutralized dicarboxylic acid monomer and water is first formed. The polymerization is then conducted by slowly feeding the nondicarboxylic acid monomer and initiator into the heel, and is carried out in the presence of at least one metal ion. However, in Yang, the feed time of the non-dicarboxylic acid monomer and initiator is at least 3 and preferably 5 to 7 hours, and the process is limited to producing polymers containing less than 55 weight percent dicarboxylic acid monomers. DE 4,008,696 A1 to Denzinger et al., herein called "Denzinger" discloses another "heel" process for making polymers that contain greater than 65 weight percent dicarboxylic acid monomers. In Denzinger, water soluble ethylenically unsaturated monomer and initiator are added to a heel of partially neutralized dicarboxylic acid monomer. Denzinger requires the final overall degree of neutralization of acid groups on all monomers be from 52 to 70 percent and preferably 55 to 65 percent to obtain less than 1.5 weight percent residual dicarboxylic acid monomer based on the total weight of polymer product. However, a major disadvantage of Denzinger is that the time for feeding the initiator and ethylenically unsaturated monomer in the examples is about six hours and the hold time after the completion of the feeds is about one to two hours for a total polymerization reaction time of 7 to 8 hours. EP-A-0 398 724 discloses a process for preparing water soluble copolymers which comprises establishing an initial charge of water in a reactor, adding 3-65 % by weight based on the total monomers of a monoethylenically unsaturated dicarboxylic acid, optionally a portion of the initiator and a neutralizer; adding a metal salt activator and running the polymerization reaction at 80-200°C. The polymerization is run at a solid level of from 20-80 % by weight; the monomer addition time is 1-10 hours and the base is added in an amount of from 20-80 equivalent percent based on the acid content of the monomers. The residual monomer content is in Example 7 0.2 %. Consequently, there is a need to be able to produce water soluble polymers containing at least 70 weight percent dicarboxylic acid monomers where the amount of unreacted dicarboxylic acid monomer in the polymer product is less than about 1.5 weight percent based on the total weight of polymer product, and where the polymerization reaction time of the process is as short as possible. We have discovered an aqueous free radical addition polymerization process for preparing a water soluble polymer product, comprising: a) forming a reaction mixture comprising at least 70 weight percent based on total weight of monomer of at least one monoethylenically unsaturated dicarboxylic acid monomer containing 4 to 10 carbon atoms or anhydride thereof, at least one base and from 5 to 20 weight percent of a total amount of at least one water soluble initiator; b) adding at least one metal promoter; and then c) feeding to the reaction mixture the remainder of the total amount of the at least one water soluble initiator, and optionally one or more other water soluble monoethylenically unsaturated monomers; wherein the total weight of optional other water soluble monomer in the final mixture is equal to or less than the total weight of monoethylenically unsaturated dicarboxylic acid monomer; wherein the amount of base is 0.9 to 1.7 equivalent moles per mole of dicarboxylic acid d) maintaining the reaction mixture at a temperature of between 80°C and 140°C and at a reaction solids level of from 50 to 65 weight percent during the polymerization, the monomer and initiator being fed for less than 6 hours; and e) recovering the polymer product, wherein the product contains less than 1.5 weight percent residual dicarboxylic acid monomer, based on the total weight of product. This improved process can, if desired, provide polymerization reaction times of about 3 hours or less while producing a water soluble polymer product containing less than 1.5 weight percent unreacted dicarboxylic acid monomer through the combination and adjustment of several process variables. The important process variable are 1) the amount of base present in the reaction mixture per mole of dicarboxylic acid during the polymerization, 2) the presence of a metal promoter in the reaction mixture during the polymerization, 3) the weight percent reaction solids during the polymerization, and 4) the reaction temperature. In addition to these process variables, the manner in which the initiator, and optional other water soluble monomer are added to the reaction mixture during the polymerization can aid in shortening polymerization reaction times and reducing the level of unreacted dicarboxylic acid monomer in the polymer product. By "percent reaction solids" we mean the total weight of solids added to the reaction mixture divided by the total weight of reaction mixture and multiplied by 100. The total weight of solids in the reaction mixture is the dicarboxylic acid monomer and its salts thereof, the optional other water soluble monomer, solid initiator, solid metal promoter, and any other solids added to the reaction mixture. By "polymerization reaction time", we mean the time required to feed the initiator and monomer to the reaction mixture plus any reaction hold time. The reaction hold time is the amount of time after the feeds have been completed where the reaction mixture is maintained at the polymerization conditions to further polymerize the monomer. In the process of the present invention, first an aqueous reaction mixture of dicarboxylic acid monomer is formed. Preferably, all the dicarboxylic acid monomer is added to the reaction mixture before feeding the one or more initiators and one or more optional water soluble monomers. However, if desired, from 20 to 50 weight percent of the total amount of dicarboxylic acid monomer added to the reaction mixture may be fed to the reaction mixture concurrently with the initiator and optional other water soluble monomer. Dicarboxylic acid monomers which are used in the process of the present invention include monoethylenically unsaturated dicarboxylic acids containing from 4 to 10, preferably from 4 to 6, carbon atoms per molecule and the anhydrides of the cis dicarboxylic acids. Examples of suitable dicarboxylic acid monomers include maleic acid, itaconic acid, mesaconic acid, fumaric acid, citraconic acid, alpha - methylene glutaric acid, and the anhydrides of cis dicarboxylic acids, such as maleic anhydride, cis-3,4,5,6-tetrahydrophthalic anhydride, and combinations thereof. Maleic anhydride and maleic acid are the most preferable of these monomers. The weight percent dicarboxylic acid monomer based on the total weight of monomers is from 70 to 100, and preferably from 85 to 100 weight percent. To the reaction mixture is also added one or more bases. For the process of the present invention, from 0.90 to 1.70 equivalent moles of base should be added per mole of dicarboxylic acid monomer. By "equivalent" we mean moles of active base that will react with one mole of acid. Overall, the preferable equivalent moles of base added per mole dicarboxylic acid monomer is 1.00 to 1.60. The amount of base added to the reaction mixture within the ranges indicated herein depends on the weight percent of dicarboxylic acid monomer desired in the polymer product. Generally, as the desired weight percent of dicarboxylic acid monomer in the polymer product increases, the amount of base added per mole dicarboxylic acid monomer should decrease within the ranges indicated. When making the polymer product formed from 100 to 70 weight percent dicarboxylic acid monomer, based on total monomer, 0.90 to 1.70 equivalent moles of base per mole dicarboxylic acid monomer is added. The one or more bases added to the reaction mixture may be for example ammonium hydroxide, or an alkali metal base such as sodium hydroxide, potassium hydroxide, or lithium hydroxide. Preferably the base is sodium hydroxide. The base may be added as a solid or liquid to the reaction mixture. In this process, all the base is usually added to the reaction mixture before the feeds of initiator and monomer are begun. By "monomer" herein we mean to include both any subsequently added dicarboxylic acid monomer and optional other water soluble monomer. The base is preferably added to the reaction mixture immediately after forming the reaction mixture of dicarboxylic acid monomer. Alternatively, the base may be added to dicarboxylic acid monomer before forming the reaction mixture. For example, disodium maleate which was formed by neutralizing maleic acid with sodium hydroxide, could be combined with a reaction mixture of maleic acid and water. In an alternative embodiment, up to half the base may be added concurrently with the feeds of initiator and monomer, either as a separate feed or with one of the monomer feeds. To the reaction mixture is also added at least one metal promoter. The metal promoter enhances the conversion of the dicarboxylic acid monomer to polymer product. Metal promoters useful in the present invention are water soluble transition metal salts such as the salts of cobalt, iron, copper, cerium, nickel, manganese, molybdenum, zirconium, vanadium, zinc, and combinations thereof. Useful water soluble metal salts must be capable of generating the metal ion in an aqueous solution and include the salts of sulfates, nitrates, chlorides, bromides, acetates, phosphates and gluconates; such as for example ferrous sulfate heptahydrate, cuprous acetate, ferrous acetate, manganese acetate, cupric acetate, ferrous and ferric chloride, ferrous and ferric phosphate, cuprous and cupric chloride, cuprous and cupric bromide, cupric nitrate, ferric sulfate, manganese bromide, manganese chloride, and combinations thereof. Preferred metal promoters are the water soluble metal salts of iron and copper and combinations thereof. The metal promoter may be added to the reaction mixture at different stages in the polymerization. For example, the metal promoter may be added to the reaction mixture before beginning the feeds of initiator and monomer, or may be gradually fed into the reaction mixture during the polymerization. If the metal promoter is fed into the reaction mixture, it may be fed to the reaction mixture in a separate stream or added to another feed and fed into the reaction mixture. If the metal promoter is fed separately, it may be fed simultaneously with the other feeds or staggered such that it begins or ends at different times from the other feeds. The concentration in the reaction mixture of the metal promoter should be from about 0.25 to about 250 parts per million (ppm) of the metal ion based on the total weight of the monomers. Preferably the concentration of metal ion is from about 1 to about 25 ppm, and most preferably from about 3 to about 20 ppm. To polymerize the reaction mixture, one or more water soluble initiators and if desired in the polymer product, one or more optional other water soluble monomers, are fed to the reaction mixture in separate feeds. As stated previously, other optional feeds include from about 20 to about 50 percent of the total weight of dicarboxylic acid monomer. These other optional feeds may be fed to the reaction mixture concurrently with the feeds of initiator and optional other water soluble monomer. The time necessary for feeding the initiator and optional other water soluble monomer depends on such process variables as the amount of base added to the reaction mixture, the amount of metal promoter added to the reaction mixture, the weight percent reaction solids during the polymerization, and the reaction temperature. Also, the manner in which the initiator and optional other water soluble monomer are added to the reaction mixture during the polymerization can aid in shortening polymerization reaction times. For the process of this invention, the time necessary for feeding the initiator and the optional other water soluble monomer is less than 6 hours, but can if desired be less than 5 hours, preferably less than 4 hours and most advantageously less than 3 hours. The other optional feeds may be fed to the reaction mixture for the same or less feed time as the initiator and the optional water soluble monomer. By increasing the feed time of initiator and monomer, the amount of unreacted dicarboxylic acid monomer will decrease, but the processing costs will increase due to increased polymerization reaction times. The initiator and optional other water soluble monomer are typically added to the reaction mixture in separate feeds concurrently for the same amount of time. For example, the initiator and optional other water soluble monomer may be fed separately and linearly (at a constant rate) into the reaction mixture over a three hour feed period. However, for improved conversion of dicarboxylic acid monomer it may be desirable to extend the feed of the initiator such that less than 10 weight percent of the total initiator feed is fed alone after all the other feeds have been completed. In the process of the present invention, a portion of the initiator is added, to the reaction mixture before beginning any of the feeds. This addition begins the polymerization reaction and is believed to aid in reacting the dicarboxylic acid monomer. The addition consists of from 5 to 20, preferably from 10 to 15, weight percent of the total initiator. Immediately after this addition, the temperature of the reaction mixture rises rapidly. Preferably, the feeds are started after the exotherm from this addition subsides. The weight percent optional other water soluble monomer based on the total weight of monomers added to the reaction mixture may be from 0 to 50, preferably from 0 to 40, more preferably 5 to 30, and most preferably 5 to 15 weight percent. The optional water soluble monomers useful in the process of the present invention include water soluble monoethylenically unsaturated monocarboxylic acids and salts thereof, monoethylenically unsaturated carboxyl-free monomers, and combinations thereof. The monoethylenically unsaturated monocarboxylic acids contain from 3 to 6 carbon atoms per molecule and include acrylic acid, methacrylic acid, vinylacetic acid, crotonic acid, and their salts, and combinations thereof. The most preferred monoethylenically unsaturated monocarboxylic acids are acrylic acid, methacrylic acid, and combinations thereof. The monoethylenically unsaturated carboxyl free monomers include alkyl esters of acrylic or methacrylic acids such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and isobutyl methacrylate; hydroxyalkyl esters of acrylic or methacrylic acids such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate; acrylamide, methacrylamide, N-tertiary-butylacrylamide, N-methylacrylamide, N,N-dimethylacrylamide; acrylonitrile, methacrylonitrile, allyl alcohol, allylsulfonic acid, allyl phosphonic acid, vinylphosphonic acid, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, phosphoethyl methacrylate, N-vinylpyrollidone, N-vinylformamide, N-vinylimidazole, vinyl acetate, styrene, vinylsulfonic acid and its salts, and 2-acrylamido-2-methylpropanesulfonic acid and its salts, and combinations thereof. Suitable water-soluble initiators for the process of the present invention are any conventional free radical water-soluble initiator, water-soluble redox initiator, and combinations thereof. The total initiator added to the reaction mixture should be from about 0.5 to about 25 weight percent based on the total amount of monomer added. Generally, as the weight percent of dicarboxylic acid monomer increases, the amount of initiator used should increase within the range of from 0.5 to 25 weight percent. For a polymer product formed from 100 to 70 weight percent dicarboxylic acid monomer, preferably about 2 to about 25 weight percent initiator should be added, based on the total weight of monomer added. Suitable free-radical initiators include hydrogen peroxide, certain alkyl hydroperoxides, dialkyl peroxides, persulfates, peresters, percarbonates, perphosphates, ketone peroxides, and azo initiators and combinations thereof. Specific examples of free-radical initiators include for example hydrogen peroxide, t-butyl hydroperoxide, di-tertiary butyl peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, sodium perphosphate, ammonium perphosphate, tertiary-amyl hydroperoxide, methylethyl ketone peroxide, 2,2-azobis(cyanovaleric acid), and combinations thereof. The free-radical initiators are preferably used in amounts of from 5 to 20 weight percent initiator based on the total monomer weight. Suitable water-soluble redox initiators include sodium bisulfite, sodium sulfite, persulfates, hypophosphites, isoascorbic acid, sodium formaldehydesulfoxylate and combinations thereof. The redox initiators are preferably used in amounts of from 0.5 to 20 weight percent and more preferably used in amounts of from 1.0 to 15.0 percent, based on the weight of total monomer. A preferred method for making the polymer product of the present invention uses a combination of both the free-radical initiator and the redox initiator. A preferable combination of initiators is persulfate and peroxide such as hydrogen peroxide and sodium persulfate. The percent reaction solids throughout the polymerization should be from 5 to 65 weight percent and preferably from 50 to 60 weight percent, based on the total weight of the reaction mixture, to achieve less than 1.5 weight percent dicarboxylic acid monomer in the polymer product in less than 6 hours. When the weight percent of dicarboxylic acid monomer is increased, the percent reaction solids should also increase. The temperature of the reaction mixture during the polymerization should be maintained slightly below the boiling point of the reaction mixture. The reaction mixture temperature should be maintained at a temperature of from 80 to 140°C, preferably from 80 to 110°C, and more preferably from 92 to 110°C during the polymerization. The reaction mixture pressure should be maintained at a pressure of from atmospheric to 275.8 Kpa (40 pounds per square inch gauge (psig)). Preferably, the reaction mixture pressure is maintained at atmospheric pressure. The polymerization may be conducted in air or any inert atmosphere such as nitrogen or argon. After the feeds are complete, the reaction mixture is maintained at the reaction temperature of 80 to 140°C for a reaction hold time of 0 to 90 minutes to allow for further conversion of dicarboxylic acid monomer. Preferably the reaction hold time is less than 60 minutes and most preferably less than 30 minutes. The process of the present invention allows for a polymerization reaction time of less than 6 hours, preferably less than 5 hours, and most preferably less than 3.5 hours. Of course as the polymerization reaction time is increased, the conversion of dicarboxylic acid monomer to polymer product will increase. At the completion of the polymerization, the residual level of dicarboxylic acid monomer in the polymer product is less than 1.5 weight percent, preferably less than 1.1 weight percent and most preferably less than 0.9 weight percent, based on the total weight of polymer product. After the polymerization, the level of residual monomer may be reduced by adding one or more initiators or reducing agents which can assist scavenging of unreacted monomer. Preferably, any post-polymerization additions of initiators or reducing agents are conducted at or below the polymerization temperature. Generally, any of the initiators suitable for the polymerization are also suitable for reducing the residual monomer content of the polymer mixture. Typically, the level of initiator or reducing agent added to reduce the residual monomer content of the polymer product is in the range of from 0.5 to 5.0, and preferably from 1.0 to 4.0 weight percent based on the total amount of monomer. After the polymerization, the polymer product may be recovered and used as is, separated by conventional techniques to isolate the polymer solids, or diluted with water to adjust the percent reaction solids to less than 40 weight percent. If desired, excess initiator in the polymer product may be reduced with one or more common reducing agents such as sodium metabisulfite or isoascorbic acid. Additionally, the pH of the polymer product may be adjusted such as for example by adding a common base such as sodium hydroxide. The molecular weight of the polymer product produced by the process of the present invention is from about 500 to about 40,000 molecular weight, preferably from about 1000 to about 30,000, more preferably from about 1000 to about 20,000, and most preferably from about 1,000 to about 10,000 as measured by gel permeation chromatography (GPC) based on a relative standard of 4500 molecular weight poly(acrylic acid). The water soluble polymer product produced by the process of the present invention is useful as an additive in cleaning compositions such as cleaning or detergent formulations used for hard surfaces; household, industrial and institutional laundry; and hand and automatic dishwashing. For example, the polymer product may be used as a builder, incrustation inhibitor, antiredeposition agent, anti-filming agent, sequestering agent, soil removal agent, and dispersant in cleaning and detergent formulations. The polymer product is also useful for scale inhibition and corrosion control in any water circulating system such as those systems used in cooling water towers, boilers, water desalination plants, sugar recovery plants, oil drilling wells, reverse osmosis equipment, steam power plants, and heat exchange equipment. The polymer product of the present invention may also be used as a dispersant for inorganic particulates such as pigments, kaolin clay, ceramics, calcium carbonate, zeolites, titanium dioxide; for aqueous emulsions such as latex paints and glazes; and for drilling muds. The polymer product is also useful as a dispersing agent in paper making. The polymer product is particularly useful as an additive in cleaning compositions such as in cleaning and detergent formulations. Cleaning and detergent formulations containing the polymer product may be in any of the usual physical forms, such as powders, beads, flakes, bars, tablets, noodles, liquids, pastes, slurries and the like. The cleaning and detergent formulations are prepared and utilized in the conventional manner and are usually based on surfactants, and optionally, on either precipitant or sequestrant builders. Suitable surfactants are, for example, anionic surfactants, such as from C 8 to C 12 alkylbenzenesulfonates, from C 12 to C 16 alkanesulfonates, from C 12 to C 16 alkylsulfates, from C 12 to C 16 alkylsulfosuccinates and from C 12 to C 16 sulfated ethoxylated alkanols and nonionic surfactants such as from C 6 to C 12 alkylphenol ethoxylates, from C 12 to C 20 alkanol alkoxylates, and block copolymers of ethylene oxide and propylene oxide. Optionally, the end groups of polyalkylene oxides can be blocked, whereby the free OH groups of the polyalkylene oxides can be etherified, esterified, acetalized and/or aminated. Another modification consists of reacting the free OH groups of the polyalkylene oxides with isocyanates. The nonionic surfactants also include C 4 to C 18 alkyl glucosides as well as the alkoxylated products obtainable therefrom by alkoxylation, particularly those obtainable by reaction of alkyl glucosides with ethylene oxide. The surfactants usable in detergents can also have an amphoteric character and they can be soaps. In general, the surfactants constitute from 2 to 50, preferably 5 to 45 percent by weight of the cleaning or detergent formulation. Liquid detergent or cleaning formulations usually contain as components liquid or even solid surfactants which are soluble or at least dispersible in the formulation. Surfactants suitable for this purpose are liquid polyalkylene oxides or polyalkoxylated compounds, products that can also be used in powdered detergents. Examples of sequestrant builders contained in the cleaning and detergent formulations can include phosphates, specifically, pyrophosphates, polyphosphates, and especially sodium tripolyphosphate. Further examples are the zeolites, sodium carbonate, poly(carboxylic acids), nitrilotriacetic acid, citric acid, tartaric acid, the salts of the aforesaid acids and the monomeric, oligomeric or polymeric phosphonates. The amounts of the individual substances used in the preparation of cleaning and detergent formulations by weight based on the total weight of the formulation are, for example, up to 85 weight percent sodium carbonate, up to 45 weight percent phosphates, up to 40 weight percent zeolites, up to 30 weight percent nitrilotriacetic acid and phosphonates and up to 30 weight percent polycarboxylic acids. In certain liquid detergent markets the use of builders is usually limited to citric acid and its salts or a combination of citrate and fatty acid soap, while in other markets liquid detergent compositions incorporate an intermediate level of soap, about 15 weight percent, or tripolyphosphate, about 20 weight percent, to assist overall cleaning efficacy. Other common additives to cleaning compositions and especially detergent formulations are bleaching agents, used in an amount of up to 30 weight percent; corrosion inhibitors, such as silicates, used in an amount of up to 25 weight percent; dye transfer inhibiting agents, used in an amount up to 20 weight percent; and graying inhibitors used in an amount of up to 5 weight percent. Suitable bleaching agents are, for example, perborates, percarbonates or chlorine-generating substances, such as chloroisocyanurates. Suitable silicates used as corrosion inhibitors are, for example, sodium silicate, sodium disilicate and sodium metasilicate. Suitable dye transfer inhibiting agents are for example poly(vinyl pyrrolidone). Examples of graying inhibitors are carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose and graft copolymers of vinyl acetate and polyalkylene oxides having a molecular weight of 1,000 to 15,000. Other common optional additives used in cleaning compositions and especially detergent formulations are optical brighteners, enzymes and perfumes. Powdered detergent formulations can also contain up to 50 weight percent of an inert diluent, such as sodium sulfate, sodium chloride, or sodium borate. The detergent formulations can be anhydrous or they can contain small amounts, for example up to 10 weight percent, of water. Liquid detergents can contain up to 80 weight percent water as an inert diluent. One or more of the polymer products produced from the process of the present invention can be added to cleaning compositions including cleaning and detergent formulations at levels where they provide the intended benefit. Generally, this level will be from about 0.5 to about 50 weight percent, preferably from about 1 to about 40 weight percent of polymer product, based on the total weight of the formulation. For example, if the polymer product is used as a builder in a detergent or cleaning formulation, the level in the formulation will be from about 5 to about 40 weight percent, based on the total weight of the formulation. In some cases, particularly when used as a soil removal agent and soil redeposition inhibitor, the amount of polymer product actually used is preferably between about 2 and 10 weight percent, based on the cleaning and detergent formulation. Of particular importance is the use of the additives according to the invention in low-phosphate detergents and cleaning agents, particularly those containing a precipitant builder such as sodium carbonate. The low-phosphate formulations contain up to a maximum of 25 weight percent of sodium tripolyphosphate or pyrophosphate. If desired, the polymer product prepared according to the process of the present invention can be used in detergent formulations together with other acrylic acid homopolymers. The acrylic acid homopolymers are currently being used as soil redeposition inhibitors in detergent formulations. The polymer product can be added to detergent and cleaning formulations in partially neutralized or completely neutralized form. Other preferred applications for the polymer product produced by the process of this invention include its use in water circulating systems. In water circulating systems, the polymer product may act as a dispersant, and may also act as an anti-nucleating agent where minor amounts of the polymer product can serve as a threshold inhibitor for crystal formation or scaling. Water circulating systems in which the polymer product is useful include those systems used for cooling water towers, boilers, water desalination plants, sugar recovery plants, oil drilling wells, reverse osmosis equipment, steam power plants, and heat exchange equipment. When used to inhibit crystal formation or scaling, the polymers are often combined with corrosion inhibitors such as inorganic or organic phosphates or phosphonates or metallic salts such as zinc compounds and the like. The polymer product can be added directly to the aqueous system in an amount of 0.1 to 500 ppm by weight. The polymer product may also be added to the system as a concentrated aqueous composition containing one or more inert diluents wherein the polymer product is present in the composition at a level of from 20 percent to 60 percent by weight. EXAMPLES The following examples are presented to illustrate the preparation of polymer product prepared according to the process of the present invention. The weight average molecular weights (Mw) and the number average molecular weights (Mn) in Examples 1 - 6 were measured by aqueous gel permeation chromatography (GPC) relative to a 4,500 Mw poly(acrylic acid) standard. Preparation of 70 Maleic Acid /30 Acrylic Acid Copolymer EXAMPLE 1 To a one liter four neck round bottom flask equipped with a stirrer, reflux condenser, thermometer, feeding system, nitrogen inlet, heating mantle and temperature control devise were added 80.00 grams of deionized water, 147.90 grams of maleic anhydride, 195.80 grams of a 50 weight percent aqueous solution of sodium hydroxide, and 5.00 grams of a 0.15 weight percent solution of iron sulfate heptahydrate (FeSO 4 .7H 2 O) dissolved in deionized water to form a reaction mixture. This reaction mixture was heated to 98 °C. Next, 7.50 grams of acrylic acid and 7.00 grams of an initiator solution consisting of 6.25 grams of sodium persulfate, 33.30 grams of 30 % hydrogen peroxide, and 20.00 grams of deionized water were added to the reaction mixture. Then, a) 67.50 grams of acrylic acid, and b) the remaining initiator solution were each fed linearly over 150 minutes. During the feeds, the reaction mixture temperature was maintained at 98 °C. At the end of the feeds, the reaction mixture was maintained at 98 °C for a reaction hold time of 30.0 minutes. The reaction mixture was cooled to 80°C and a solution containing 7.50 grams sodium metabisulfite in 25.00 grams of deionized water was added followed by the addition of 90.00 grams of deionized water. The resulting polymer product had a molecular weight, and weight percent residual maleic acid content as reported in Table 1. EXAMPLE 2 To a two liter four neck round bottom flask equipped with a stirrer, reflux condenser, thermometer, feeding system, nitrogen inlet, heating mantle and temperature control devise were added 184.00 grams of deionized water, 296.00 grams of maleic anhydride, and 386.00 grams of a 50 weight percent aqueous solution of sodium hydroxide to form a reaction mixture. This reaction mixture was heated to 98 °C. Next, 20.00 grams of a 0.15 weight percent solution of iron sulfate heptahydrate (FeSO 4 .7H 2 O) dissolved in deionized water was added to the reaction mixture. Then, 22.50 grams of acrylic acid and 14.00 grams of an initiator solution consisting of 25.00 grams of sodium persulfate, 83.00 grams of 30 weight percent aqueous solution of hydrogen peroxide, and 30.00 grams of deionized water were added to the reaction mixture. Then, a) 127.50 grams of acrylic acid, and b) the remaining initiator solution were each fed linearly over 180 minutes. At the end of the feeds, the reaction mixture was maintained at 98 °C for a reaction hold time of 30.0 minutes. The reaction mixture was cooled to 70°C and a solution containing 10.00 grams sodium metabisulfite in 20.00 grams of deionized water was added followed by the addition of 75.00 grams of deionized water and 2.50 grams of 30 weight percent aqueous solution of hydrogen peroxide. The resulting polymer product had a molecular weight and weight percent residual maleic acid content as reported in Table 1. EXAMPLE 3 To a one liter four neck round bottom flask equipped with a stirrer, reflux condenser, thermometer, feeding system, nitrogen inlet, heating mantle and temperature control devise were added 88.30 grams of deionized water, 147.90 grams of maleic anhydride, 120.70 grams of a 50 weight percent aqueous solution of sodium hydroxide, and 5.00 grams of a 0.15 weight percent solution of iron sulfate heptahydrate (FeSO 4 ·7H 2 0) dissolved in deionized water to form a reaction mixture. This reaction mixture was heated to 100 °C. Next, 24.00 grams of an acrylic acid solution consisting of 75.00 grams of acrylic acid, 75.00 grams of a 50 weight percent aqueous solution of sodium hydroxide, and 90.00 grams of deionized water, and an initiator solution consisting of 0.57 grams of sodium persulfate and 3.33 grams of 30 % hydrogen peroxide were added. Then, the remaining acrylic acid solution, and a second initiator solution consisting of 5.07 grams sodium persulfate and 30.00 grams of 30 % hydrogen peroxide were each fed linearly over 150 minutes. During the feeds, the reaction mixture temperature was maintained at 100 °C. At the end of the feeds, the reaction mixture was maintained at 100 °C for a reaction hold time of 30.0 minutes. The resulting polymer product had a molecular weight and weight percent residual maleic acid content as reported in Table 1. Examples 1, 2 and 3 illustrate methods for preparing a polymer product formed from 70 weight percent maleic acid and 30 weight percent acrylic acid using the process of the present invention. Examples 1 and 2 also demonstrate that the polymerization reaction time may be lowered from 3.5 hours to 2.5 hours while still maintaining the low residual maleic acid content in the polymer product. Preparation of 80 Maleic Acid/20 Acrylic Acid Copolymer COMPARATIVE EXAMPLE 1 To a two liter round bottom flask equipped with a stirrer, reflux condenser, thermometer, feeding system, nitrogen inlet, heating mantle and temperature control devise were added 86.20 grams of deionized water, 427.60 grams of a 50 weight percent aqueous solution of sodium hydroxide, and 338.00 grams of maleic anhydride to form a reaction mixture. This reaction mixture was heated to 98 °C. To the reaction mixture, a) 100.00 grams of acrylic acid in 110 grams of deionized water was added linearly over 94 minutes and b) an initiator solution consisting of 20.00 grams of sodium persulfate, 66.60 grams of a 30 weight percent aqueous solution of hydrogen peroxide, and 93.40 grams deionized water was fed linearly over 112.5 minutes. During the feeds, the the reaction mixture temperature was maintained at 98 °C. At the end of the feeds, the reaction mixture was maintained at 98°C for a reaction hold time of 37.5 minutes. The resulting polymer product had a molecular weight and weight percent residual maleic acid as reported in Table 1. EXAMPLE 4 To the reactor described in Comparative Example 6 were added 43.00 grams of deionized water, 213.80 grams of a 50 weight percent aqueous solution of sodium hydroxide, and 169.00 grams of maleic anhydride to form a reaction mixture. This reaction mixture was heated to 98 °C. Next, 10 grams of a 0.15 weight percent solution of iron sulfate heptahydrate (FeSO 4 ·7H 2 0) dissolved in deionized water was added to the reaction mixture. Then, 7.50 grams of acrylic acid and 5.75 grams of an initiator solution consisting of 10.00 grams of sodium persulfate, 33.30 grams of 30 weight percent aqueous solution of hydrogen peroxide, and 14.60 grams of deionized water were added. Following this addition, a) 42.50 grams of acrylic acid in 10.60 grams of deionized water, and b) the remaining initiator solution were each fed linearly over 120 minutes. During the feeds, the reaction mixture temperature was maintained at 98 °C. At the end of the feeds, the reaction mixture was maintained at 98 °C for a reaction hold time of 30.0 minutes. The resulting polymer product had a molecular weight and weight percent residual maleic acid content as reported in Table 1. EXAMPLE 5 To the reactor described in Comparative Example 6 were added 338.00 grams of maleic anhydride, 165.00 grams of deionized water, and 330.90 grams of a 50 weight percent aqueous solution of sodium hydroxide to form a reaction mixture. This reaction mixture was heated to 98 °C. Next, 20 grams of a 0.15 weight percent solution of iron sulfate heptahydrate (FeSO 4 ·7H 2 0) dissolved in deionized water was added to the reaction mixture. Then, 15.00 grams of acrylic acid and 12.00 grams of an initiator solution consisting of 20.00 grams of sodium persulfate, 66.60 grams of 30 weight percent aqueous solution of hydrogen peroxide, and 33.00 grams of deionized water were added to the reaction mixture. Following this addition, a) 85.00 grams of acrylic acid in 21.25 grams of deionized water, and b) the remaining initiator solution were each fed linearly over 120 minutes. During the feeds, the the reaction mixture temperature was maintained at 98 °C. At the end of the feeds, the reaction mixture was maintained at 98 °C for a reaction hold time of 30.0 minutes. The resulting polymer product had a molecular weight and weight percent residual maleic acid as reported in Table 1. EXAMPLE 6 To the reactor described in Comparative Example 6 were added 172.00 grams of deionized water, 270.40 grams of maleic anhydride, and 264.70 grams of a 50 weight percent aqueous solution of sodium hydroxide to form a reaction mixture. This reaction mixture was heated to 98 °C. Next, 4.00 grams of a 0.15 weight percent solution of iron sulfate heptahydrate (FeSO 4 ·7H 2 0) dissolved in deionized water was added to the reaction mixture. Then, 12.00 grams of acrylic acid and 10.00 grams of an initiator solution consisting of 18.00 grams of sodium persulfate, 60.00 grams of 30 weight percent aqueous solution of hydrogen peroxide, and 25.00 grams of deionized water were added to the reaction mixture. Following this addition, a) 68.00 grams of acrylic acid in 17.00 grams of deionized water, and b) the remaining initiator solution were each fed linearly over 180 minutes. At the end of the feeds, the reaction mixture was maintained at 98 °C for a reaction hold time of 30.0 minutes. The reaction mixture was cooled to 70°C and a solution of 9.30 grams of sodium metabisulfite in 20.00 grams of deionized water was added followed by the addition of 150.00 grams of deionized water. The pH of the reaction mixture was adjusted to a pH of 7.0 with the addition of 125.00 grams of a 50 weight percent aqueous solution of sodium hydroxide. The resulting polymer product had a molecular weight and weight percent residual maleic acid content as reported in Table 1. Examples 4, 5, and 6 illustrate methods for preparing a polymer product formed from 80 weight percent maleic acid and 20 weight percent acrylic acid using the process of the present invention. Example 4 compared with Comparative Example 1 demonstrates that a metal promoter is needed to achieve low residual maleic acid content when the polymerization reaction time is reduced to 2.5 hours. Examples 5 and 6 demonstrate that when 1.20 moles of NaOH are added per mole of maleic acid monomer, the residual maleic acid content is kept below 1 weight percent while maintaining a polymerization reaction time of less than 3 hours. Preparation of Copolymers Greater than 90 Weight Percent Maleic Acid EXAMPLE 7 To a one liter four neck round bottom flask equipped with a stirrer, reflux condenser, thermometer, feeding system, nitrogen inlet, heating mantle and temperature control devise, were added 50.00 grams of deionized water, 187.40 grams of a 50 weight percent aqueous solution of sodium hydroxide, and 226.50 grams of maleic acid to form a reaction mixture. This reaction mixture was heated to 98 °C, at which time 6.00 grams of a 0.15 weight percent solution of iron sulfate heptahydrate dissolved in deionized water and 1.32 grams of a 0.15 weight percent solution of copper sulfate pentahydrate dissolved in deionized water was added to the reaction mixture. Next, an initiator solution was prepared by combining of 20.00 grams of sodium persulfate and 67.00 grams of 30 weight percent aqueous solution of hydrogen peroxide. Then, 2.50 grams of acrylic acid and 9.00 grams of the initiator solution were added to the reaction mixture. Following this addition, 2 separate feeds were started of 1) the remaining initiator solution, and 2) 21.00 grams of acrylic acid. The initiator solution and acrylic acid were fed linearly over 120 minutes while maintaining the reaction mixture temperature at 98 °C. After the feeds were complete, the reaction mixture was held at a temperature of 98 °C for 30 minutes. The reaction mixture was cooled to 80°C and a solution of 6.00 grams of sodium metabisulfite and 25.00 grams of deionized water was added. The molecular weight of the polymer product is reported in Table 1. The weight percent residual maleic acid is also reported in Table 1 as measured before the 30 minute hold. EXAMPLE 8 To a one liter four neck round bottom flask equipped with a mechanical stirrer, reflux condenser and addition funnels, were added 83.40 grams of deionized water, 211.40 grams of maleic anhydride, and 189.50 grams of a 50 weight percent aqueous solution of sodium hydroxide to form a reaction mixture. This reaction mixture was heated to 98 °C, at which time 6.00 grams of a 0.15 weight percent solution of iron sulfate heptahydrate dissolved in deionized water and 1.30 grams of a 0.15 weight percent solution of copper sulfate pentahydrate dissolved in deionized water were added to the reaction mixture. Next, an initiator solution was prepared by combining of 20.00 grams of sodium persulfate and 125.00 grams of 30 weight percent aqueous solution of hydrogen peroxide. Then, 5.00 grams of 30 weight percent aqueous solution of hydrogen peroxide and 15.00 grams of the initiator solution were added to the reaction mixture. Next, the remainder of the initiator solution was fed linearly over 180 minutes while maintaining the reaction mixture temperature at 98 °C . After the initiator feed was complete, the reaction mixture was held at a temperature of 98 °C for 30 minutes. The reaction mixture was cooled to 80°C and a solution of 7.00 grams of sodium metabisulfite and 25.00 grams of deionized water was added. The molecular weight and weight percent residual maleic acid are reported in Table 1. Examples 7 and 8 illustrate methods for preparing a polymer product formed from greater than 90 weight percent maleic acid using the process of the present invention. POLYMERIZATION RESULTS OF EXAMPLES 1-11 Example Composition Mw Wt% Residual Maleic Rxn Time (hrs) Wt % Rxn Solids Ratio Mol Base/Mol Dicarb PPM of Metal Ex. 1 70 MAL/ 30 AA 3710 0.03 3.5 54.7 1.62 6.00 Ex. 2 70 MAL / 30 AA 3630 0.01 2.5 52.7 1.60 12.00 Ex. 3 70 MAL / 30 AA 3880 0.11 3.0 48.7 1.60 6.00 Comp. Ex.1 80 MAL/ 20 AA 3780 1.82 2.5 52.7 1.55 0.00 Ex. 4 80 MAL / 20 AA 3280 0.34 2.5 59.1 1.55 12.00 Ex. 5 80 MAL / 20 AA 3380 0.32 2.5 56.2 1.20 12.00 Ex. 6 80 MAL / 20 AA 3280 0.86 3.0 54.2 1.20 3.00 Ex. 7 91 MAL/ 9 AA 1820 0.77 2.5 52.2 1.20 9.00 Ex. 8 100 MAL 1180 0.16 3.5 50.6 1.10 9.00 Key to TABLE 1: AA Percent by weight acrylic acid MAL Percent by weight maleic acid CALCIUM SEQUESTRATION Polymer products produced by the process of the present invention are useful for sequestering alkaline earth metals as shown in TABLE 2. Several polymer products were measured for calcium sequestration by the following procedure: a) A sample solution containing 300 ppm of polymer solids was prepared by adding 1.8 grams of a polymer product containing 5 weight percent polymer solids to 300 ml of a 0.008 M NaCl solution. The pH of the sample solution was adjusted to a pH of 10 by adding 2 weight percent solution of NaOH. b) The sample solution was titrated with 15,000 ppm CaCl 2 as CaCO 3 to a 10 ppm calcium end point using a Brinkman 672 Titroprocessor equipped with a calcium sensitive electrode and connected to a Metrohm 655 Dosimat. c) The calcium sequestration values shown in TABLE 2 are reported as milligrams calcium as CaCO 3 per gram polymer solids. CALCIUM SEQUESTRATION PROPERTIES Polymer Product From Composition Mw Ca ++ Sequestration Comparative Acusol® 445N 100 AA 4,500 365 Example 3 30 MAL/70 AA 3800 468 Example 1 50 MAL /50 AA 14,500 489 Key to TABLE 2: AA Percent by weight acrylic acid MAL Percent by weight maleic acid The results show that the polymer products made by the process of the present invention may sequester calcium as CaCO 3 per gram polymer solids more effectively than polyacrylic acid of 4500 molecular weight. INCRUSTATION INHIBITION The polymer products made by the process of the present invention are useful as incrustation inhibitors. The polymer products were tested for incrustation inhibiting properties by the following method: Test fabrics and 347 grams of ballast (cotton and cotton/polyester t-shirts) were laundered in a Kenwood Mini E European style home washing machine. The test fabrics laundered were a) 4 - 4'' X 4'' Krefeld, b) 4 - 4'' X 4'' small terry , and c) 1- 12'' X 12'' terry wash cloth all obtained from Test Fabrics in Middlesex, New Jersey. The test fabrics and ballast were laundered for 10 cycles with 90°C wash water which had a hardness of 300 ppm Ca/Mg (weight ratio Ca/Mg of 3 / 1) using 6.5 grams of the detergent formulation shown in Table 3 per liter of wash water. The test fabrics were air dried and ashed at 800°C for 2 hours. The inorganic content (incrustation) was determined and the results are shown in Table 4. Test Detergent Formulation 8 wt% Linear Alkyl Benzene Sulfonic Acid 3 wt% Tergitol® 24-L-60 4 wt% Na silicate (weight ratio 3.22 SiO 2 : 1 Na 2 O) 20 wt% Na perborate 15 wt% Na carbonate 23 wt% Zeolite® 4A 15 wt% Na sulfate 3 wt% Stearic Acid 1 wt% Foamaster® DS 4 w% Water 4 wt% Polymer Product as polymer solids EFFECTIVENESS OF POLYMER PRODUCT IN INHIBITING INCRUSTATION Percent Ash Polymer Product From: Composition Mw Krefeld Small Terry Terry Wash Cloth Example 3 70 MAL/30 AA 1.97 1.93 1.31 Key to TABLE 4: AA Percent by weight acrylic acid MAL Percent by weight maleic acid Table 4 shows that the polymer products produced by the process of the present invention are useful in detergent formulations for inhibiting incrustation in laundry applications. PERFORMANCE IN AUTOMATIC DISHWASHERS Test Method This test method measures the build-up of spotting and filming on glassware when using automatic dishwashing detergents containing the polymer product. Glass tumblers were given five cycles in a dishwasher, in the presence of food soils, and the levels of spotting and filming allowed by the detergents under test were compared visually. A Miele Model G590SC machine was used to perform the washing tests. The bottom rack of the dishwasher was randomly loaded with 10-15 dinner plates and the top rack was randomly loaded with several beakers, bowls, and cups. Four new 10 ounce glass tumblers were placed randomly on the top racks as the test glasses. Soil used in the test was a mixture of 80 percent Parkay® Margarine and 20 percent Carnation® Non-fat Dry milk. When a test was ready to be started, the soil was smeared across the plates on the bottom rack, and the machine was started on its economy wash cycle which consists of the following: 1) a prerinse, 2) a main wash, 3) two rinses, and 4) dry cycle. After the prerinse, the machine was opened and a 60 gram detergent aliquot was placed in the detergent dispenser cup for the main cycle, and the water hardness, which is normally at 200 ppm hardness with a Ca ++ to Mg ++ weight ratio of 2:1, was adjusted to 400 ppm maintaining the same Ca ++ to Mg ++ ratio. The detergent formulation used is shown in TABLE 6 and the concentration of the detergent for each main wash was 3333 ppm. The temperature of the supply water was maintained at 130° F. The machine was then allowed to complete the economy wash cycle including the drying time. This procedure was followed for a total of five complete economy wash cycles for each set of test glasses. When the final drying cycle was completed, the door was opened and the four glasses were removed and evaluated for filming and spotting. The test glasses were evaluated by placing them in light box equipped with a fluorescent light. The glasses were ranked according to the Film Rating System summarized in Table 5. The average rating for the four glasses is reported below in Table 7 for polymer products produced by the process of the present invention: FILM AND SPOT RATING SYSTEM Value FILMING RATING SPOT RATING 0 No film No spots 1 Barely perceptible Barely perceptible 2 Slight Slight 3 Moderate Moderate 4 Heavy Heavy AUTOMATIC DISH DETERGENT FORMULATION TESTED (by weight) 20.0% sodium carbonate 10.0% sodium citrate.2H 2 O 15.0% perborate.4H 2 O 25.0% Britesil® H20 Silicate (2.0 SiO 2 : 1Na 2 O) 0.5 % Enzyme 3% Olin Polytergent ® SLF-18 surfactant 5% polymer product as polymer solid diluted to 100% with sodium sulfate PERFORMANCE IN AUTO DISH DETERGENT FORMULATIONS Polymer Product From Composition of Reaction Mixture Mw Film Spot No Polymer --- 2.0 1.0 Comp.- Acusol® 445N 100 AA 4,500 0.0 0.5 Example 2 70 MAL / 30 AA 3630 0.75 0 Example 6 80 MAL / 20 AA 3510 0.5 0 Key to TABLE 7: AA Percent by weight acrylic acid MAL Percent by weight maleic acid The results in Table 7 show that the polymer products produced by the process of the present invention are effective in inhibiting the formation of spots and film in dishwashing detergent formulations.

Claims: An aqueous free radical addition polymerization process for preparing a water soluble polymer product, comprising: a) forming a reaction mixture comprising at least 70 weight percent based on total weight of monomer of at least one monoethylenically unsaturated dicarboxylic acid monomer containing 4 to 10 carbon atoms, or anhydride thereof, at least one base and from 5 to 20 weight percent of a total amount of at least one water soluble initiator; b) adding at least one metal promotor; and then c) feeding to the reaction mixture the remainder of the total amount of the at least one water soluble initiator, and optionally one or more other water soluble monoethylenically unsaturated monomers; wherein the total weight of optional other water soluble monomer in the final mixture is equal to or less than the total weight of monoethylenically unsaturated dicarboxylic acid monomer; wherein the amount of base is 0.90 to 1 .70 equivalent moles per mole of dicarboxylic acid d) maintaining the reaction mixture at a temperature of between 80°C and 140°C and at a reaction solids level of from 50 to 65 weight percent during the polymerization, the monomer and initiator being fed for less than 6 hours; and e) recovering the polymer product, wherein the product contains less than 1.5 weight percent residual dicarboxylic acid monomer, based on the total weight of product. Process according to claim 1, wherein up to half the total monoethylenically unsaturated dicarboxylic acid monomer is fed into the reaction mixture during the polymerization step. Process according to claim 1 or 2, wherein from 10 to 15 weight percent of the total initiator is added to the reaction mixture before any of the feeds is commenced. Process according to any of claims 1 to 3 wherein from 10 to 20, preferably from 10 to 15, weight percent of the total optional other water soluble monomer is added to the reaction mixture before any of the feeds is commenced. Process according to any preceding claim, wherein all the base is added to the reaction mixture before any of the feeds is commenced. Process according to any preceding claim, wherein the total amount of dicarboxylic acid monomer forms 85 weight percent of the polymer product. Process according to any preceding claim, wherein the initiator and monomer are fed for less than 4 hours, preferably less than 3 hours.

Inventors: FIARMAN IRWIN STANLEY, MCCALLUM III THOMAS FRANCIS, WEINSTEIN BARRY, FIARMAN, IRWIN STANLEY, MCCALLUM III, THOMAS FRANCIS, WEINSTEIN, BARRY
Applicants: ROHM & HAAS, ROHM AND HAAS COMPANY
Application year: 1995
Main classification: C08F22
IPC codes: C08F22, C08F220, C08F4, C11D3, C08F2