Maleic anhydride copolymers

Abstract: Transesterified copolymers of maleic anhydride, particularly useful in the field of detergency and as anti-scaling agents, obtained from pre-formed copolymers of maleic anhydride with vinyl acetate, by at least partial transesterification of said pre-formed copolymers.

Description: The invention relates to transesterified copolymers of maleic anhydride with vinyl acetate, particularly useful in the field of detergency and as anti-scaling agents. The action of sequestering agents in the presence of drinking water, or of untreated industrial water, is well known; these agents, by formation of complexes with polyvalent metal ions (for instance alkaline-earth metal ions), which cause water hardness, or with other heavy ions, hinder the formation of precipitates, thus avoiding scale (incrustation) deposition; in plants where water is warmed, such as boilers or heat-exchangers, the above mentioned agents hinder, as is known, the scale formation on the metal surface. During home-washing and industrial cleaning, polyvalent metal ions may interact with the anions present in the soil and with the anions dissolved by the detergent; in this case also the scaling (incrustation) action of the mentioned agents on the fabric fibers is known. When control agents are not present, the incrustation increases the ash contents, wash by wash, causing undesired matting and grey coloration. A compound used for many years (showing an excellent activity against the formation of precipitates and inhibiting the re-deposition of solid particles and soil on fabrics) is sodium tripolyphosphate. However, it is known that this compound, by its degradation in water, gives rise to phosphates, which in turn favour the anomalous growth of algae in inland waters and seas, thus contributing to the phenomenon known as eutrofication and to the consequent reduction (in the most serious cases exhaustion) of the oxygen content in waters, with imaginable ecological consequences. That is why, in many countries, laws were introduced in order to limit or to forbid the use of sodium tripolyphosphate in detergents. Other compounds having a fair complexing and anti-precipitation activity against soil (and insoluble salts) are aminocarboxylic acids, eg the sodium salts of nitrilotriacetic acid (NTA) and of ethylenediaminotetra-acetic acid (EDTA). However, these compounds show some drawbacks and so have limited use, such as the presence of nitrogen in the molecule since nitrogen has a role in the eutrofication process. The reduction of the Na-tripolyphosphate content in detergents has become possible by the use of gradually increasing amounts of Zeolite 4A (a particular sodium aluminosilicate) with substitution ratios higher than 1:1 of zeolite:sodium tripolyphosphate. In order to get a more effective and complete activity of the detergent formulations having low phosphorous contents, the presence of agents other than zeolite, and/or coadjuvants of detergency, showing a particular action, is also required. The Applicants have now found new and more effective chemical intermediates, which do not contain either phosphorous or nitrogen atoms in their structure and which consist solely of C, H and O atoms, exhibiting reasonable effectiveness, so that they can be used as sequestering agents, or generally as coadjuvants, and furthermore as anti-scaling agents in processes involving the heating of drinking and industrial waters. Furthermore, the new intermediates can be used to great advantage in detergency processes, where the presence of alkaline-earth ions, already in the cold, may give rise to the precipitation of insoluble salts because of the interaction of some components of the detergent and as the result of heating processes, thus forming precipitates typical of hard water. These intermediates are derivatives of the maleic anhydride-vinyl acetate copolymers, hereinafter MA-VA copolymers, which show superior technological properties in comparison with the (hydrolysed) copolymers used in the past and described for instance in GB-A-1,385,131. The copolymerisation of maleic anhydride with vinyl acetate has been known for many years. See for example the work of WILDE and SMETS, in the Journal of Polymer Science [vol. V, No. 2 (1949)], concerning the determination of the values r₁ and r₂ (reactivity ratios) in the copolymerisation of maleic anhydride with different monomers (among which was vinyl acetate). More recently [see J. Macromol. Sci-Chem. A 9(1) pp.29-43 (1975)] Caze and Loucheux have carried out research on the alternating radical copolymerisation of a charge transfer complex or adduct, which reacts further during the polymerisation. Still more recently Caze and Loucheux, [J. Macromol. Sci.-Chem.A 15(1), pp. 95-105 (1981)] have carried out further research on the microstructure of these copolymers, showing alternation between the two comonomers, independently of the feed composition. The alternate and regular structure of the comonomers is very important, in order to obtain good dispersing and complexing properties. GB-A-537709 discloses copolymers of maleic anhydride with vinyl acetate and a reaction of such copolymers to obtain materials suitable for use in the manufacture of photographic film. In this citation reactions are disclosed in which the copolymer is reacted in the presence of a strong acid, resulting in almost complete transesterification. According to the present invention a process for the manufacture of a transesterified copolymer of maleic anhydride is described in which a copolymer of maleic anhydride and vinyl acetate is prepared and the thus preformed copolymer is then at least partially transesterified, characterised in that the degree of transesterification is from 10 to 80%. According to the present invention novel transesterified copolymers of maleic anhydride are obtainable by the process described above. The transesterification of said preformed copolymers is at least partial, the degree of transesterification being from 10 to 80% and preferably from 15 to 50%. It has surprisingly been found that the dispersing and anti-precipitating action of the copolymer of maleic anhydride with vinyl acetate reaches optimum values after a partial transesterification treatment, which makes only a few groups of free vinyl alcohol in the chain available, while a share of unconverted vinyl acetate still remains present. This allows the amount of copolymer, in a detergent or anti-scaling formulation, to be much lower than in the past. The new copolymers show excellent technological properties when their average molecular weight is from 1000 to 100,000 (preferably from 2,000 to 50,000), the polydispersity ratio being from 2 to 5; they can be obtained from the parent (preformed) copolymer by transesterification with an aliphatic or cycloaliphatic alcohol, and preferably with a saturated aliphatic alcohol having from 1 to 4 C atoms, in particular methanol, ethanol, isopropanol, n-propanol and butanol. The transesterification treatment must not be drastic, but mild, in order to convert a portion of the vinyl acetate units (present in the chain) into vinyl alcohol units, thus allowing, at the same time, formation of the acetic ester of the alcohol used; in this way, a methyl, ethyl, isopropyl or butyl acetate is formed, which is then recovered together with the alcohol excess. An advantage of the present invention is that the sodium acetate, formed when the base copolymer undergoes a drastic treatment (hydrolysis) with aqueous NaOH, is minimised or eliminated; sodium acetate is an undesireable by-product, because it remains within the copolymer and its removal is never easy or complete. The parent copolymer, which is to be transesterified, can be used in a dry form, eg as a powder. The recovery of the copolymerisation solvent, eg toluene, from the parent copolymer, can be carried out before or at the end of the transesterification and takes place without any catalyst, because the acidic groups formed by the opening of the maleic ring already exhibit a satisfactory catalytic activity. Usually, during the transesterification, the copolymer dissolves in the (alcoholic) reaction liquid. The degree of transesterification can be controlled by adjusting the excess of alcohol, the reaction temperature and the reaction time. According to the present invention detergent formulations are provided comprising the transesterified copolymers described above. The new copolymers can be used in liquid formulations, requiring both compatibility (miscibility) of the copolymers with the detergent liquid system and their non-interference with any enzyme involved, during the storage of the detergent. The de-activation of enzymes used in aqueous liquid detergent formulations and in the presence of co-adjuvants is generally attributed to the removal of calcium ions from the system, which are one of the most effective stabilizers of the enzymes. By varying the degree of transesterification, it is possible to obtain the desired products with a reduced pKCa, in order to maintain a restricted but not a null value of free calcium ions, to produce such conditions so as to avoid precipitation (caused by other chemical agents present in the formulation). Moreover, the use of enzymes, protected by means of dispersion in hydrofuge oils, allows a synergism in limiting the decrease of the calcium ions present in the enzyme. Obviously, the above mentioned formulations may contain anionic, non-ionic, amphoteric or zwitterionic surfactants; soaps; builders; solubilizers; enzymes; perfumes; dyestuffs; protective agents; and so on. The copolymers can be used in the field of powder formulations, by addition of copolymer solutions to the suspensions fed to a spray drying plant. In this case no problem of interference with the enzymes (used in the form of granules and therefore protected) exists, because of the absence of the continuous liquid phase which favours mass-transfer. The powder detergent formulations we are referring to usually consist of many components, selected for instance from anionic surfactants eg. LAS, alphasulfomethylesters, alkylsulfates, alkyl polyethoxysulfates; non-ionic surfactants eg. ethyoxylated alcohols, ethoxylated nonyl-phenols, sugar esters, alkyl-polyglucosides; soaps; builders eg. zeolites, citric acid, NTA, sodium carbonate; stabilizers eg. sodium silicate, EDTA-Na, magnesium silicate; bleaching agents eg. sodium perborate mono- and/or tetrahydrate, percarbonate; bleaching activators eg. PAG, TAED, TAGU, NOFSNA; inhibitors of the grey coloration eg, carboxymethylcellulose (CMC); inorganic salts eg. Na₂SO₄. Other generally used components are optical brighteners, perfumes, coloured speckles. (NOFSNA means nonanoyl-phenolsulfonate, the sodium salt.) The amount of copolymer to be used in liquid and powder detergents is generally beween 0.5 and 15%, preferably between 1 and 8% by weight. The amount of copolymer to be added to water to avoid scale is generally from 0.1 to 1,000 ppm and preferably from 1 to 100 ppm. The polymers to be transesterified are copolymers of maleic anhydride with vinyl acetate, exactly alternated, or copolymers where, besides the two mentioned monomers in equimolar amount, limited amounts of other mono-unsaturated monomers, or termonomers, eg acrylic acid, methacrylic acid, acrylates (methyl, butyl, ethyl or hydroxyethyl acrylates), itaconic acid, methyl-vinyl ether and vinyl acetate itself, are added, in amounts from 0.05 to 1 mol per mol of maleic anhydride. The copolymers and terpolymers of the invention can be obtained by semi-continuous or continuous polymerization (or terpolymerization respectively), after having prepared an exactly equimolar adduct of maleic anhydride and vinyl acetate, by continuously feeding into the reaction system said adduct, the termonomer (if any) and the desired catalytic system. The reaction medium to be used, for the copolymerization or terpolymerization, is generally an organic liquid of low or intermediate polarity, which limits the interactions with the monomers and with the catalytic system; this liquid must be a solvent for maleic anhydride and/or for its adduct with vinyl acetate, but is preferably a non-solvent for the subsequently formed copolymer. Typical solvents include aromatic hydrocarbons eg benzene, toluene, ethylbenzene; halogenated aromatic hydrocarbons, eg monochlorobenzene; cycloaliphatic solvents eg cyclohexane; mixtures of aromatic and cycloaliphatic hydrocarbons; aliphatic halogenated hydrocarbons eg chloroform, dichloroethane, carbon tetrachloride, methylene chloride. Also low- boiling point halogenated hydrocarbon solvents, such as methylchloride, could be used but it would be necessary to work under pressure. Aliphatic ketones eg acetone, methyl-ethyl ketone can be used, but this may result in the formation of a solution or a strongly swelled suspension of the formed copolymer. Mixtures of these solvents can be used. The polymerisation temperature is between room temperature and 150°C, preferably between 50° and 120°C, to avoid working under pressure and to have kinetics suitable for industrial purposes. The transesterification temperature is generally from 50° to 150°C, preferably from 65° to 120°C. Radical initiators for these co- and terpolymerisations are those generally used in radical (solution) polymerisations, such as azoderivatives, in particular azobis-isobutyronitrile; acyl peroxides eg. benzoyl peroxide or lauroyl peroxide; peresters; dialkylperoxides; peroxycarbonates (percarbonates); hydroxyperoxides and mixtures thereof. The choice of the initiator is also dependent on the reaction temperature, which in turn controls the optimum value of the semitransformation time (time necessary for decomposing 50% of the initiator). Other details on these initiators are reported in EP-A-103,254. The radical initiator is generally added in an amount between 0.05 and 5% by weight, preferably between 0.5 and 2.5% by weight, of the overall monomers. During the copolymerisation, a solid is formed, which remains suspended in the reaction solvent, from which it is separated at the end of the reaction; the separation can be carried out by means of filtration or centrifugation and the solid product is then dried, especially if it is directly used in detergent formulations. The following examples serve to illustrate the present invention. The methods used for the determination of the parameters mentioned in the examples are: calcium binding capacity: HAMPSHIRE TEST, mentioned in DE-A-1,904,941, corresponding to GB-A-1,296,413; dispersing capacity: BASF METHOD described in a paper by F. RICHTER and E.W. WINKLER on TENSIDE, SURFACTANTS AND DETERGENTS, 24 (4); page 213 (1987); "threshold inhibition" or "crystal modification"; see the paper by G. McGrew published on CHIMICA OGGI (1986); No. 10, page 57; complexing capacity; the determination of the chelating properties was carried out using a calcium ion (Ca⁺⁺) selective electrode, as described in ANALYTICAL LETTERS vol. 4 (10); pp. 653-663 (1971); transesterification level; the ¹H-NMR spectrometric method (protons in deuterated H₂O; determination of percentage of vinyl alcohol units) was used. EXAMPLE 1 This example was carried out in a 2 litre glass reactor, provided with stirrer, thermometer, reflux condenser and thermostating jacket. The solutions of the monomers were separately prepared (49 g of maleic anhydride and 43 g of vinyl acetate in 320 cm³ toluene); a solution of the initiator (azobis-isobutyronitrile) in toluene was also separately prepared and this solution was mixed with the monomer solutions in such an amount that, 1% of the initiator calculated on the overall monomers resulted. 30% of solution of monomers and initiator was transferred into the reactor and the temperature was raised to 90°C; the continuous feeding of the remainder of the solution was began immediately. From the start the polymer separated in the form of small, suspended, solid particles. After 1 h, having completed the addition of both catalyst and monomers, the reactor was heated at 110°C under vigorous stirring for one further hour, in order to minimise the content of free monomer; after cooling, the suspension of the solid in the solvent (about 18.5% b.w.) was discharged. The content of free monomer corresponded to a 98.6% conversion. The suspension was cold filtered and the cake was washed with petroleum ether and then dried. 90.7 g of solid were recovered and the molecular weight was determined by gel permeation chromatography (GPC), as well as the necessary finishing, in order to make the solid suitable for detergency and for water treatment. The weight average molecular weight (Mw) was 38,000 and the number average molecular weight (Mn) was 11,600. EXAMPLE 2 Example 1 was repeated, replacing the toluene solvent by ethylbenzene and using as the radical initiator benzoyl peroxide, in an amount corresponding to 2.25% b.w. of the overall monomers . A portion, corresponding to 30% of the monomers and of the initiator, was fed into the reactor at the beginning of the operation; the remaining portion was fed continuously during 1.5 h, while keeping the temperature constant at 90°C. After having stirred for one further hour (always at 90°C), the resulting suspension was cooled, discharged and filtered off; the collected solid (89.9 g) was washed with petroleum ether and dried. The GPC measurement showed that Mw was 11,575 and Mn was 3650. EXAMPLE 3 Example 1 was repeated, also feeding 10.2 g of acrylic acid (11% b.w., on the maleic anhydride and vinyl acetate adduct) continuously into the reactor, previously diluted with a small amount (30 g) of toluene; after continuous feeding for 2 hours and one further hour under reflux, in order to complete the reaction, cooling, filtration, washing and drying were carried out; 97.8 g of a powder copolymer (Mw = 48,000; Mn = 12,800) were obtained. EXAMPLE 4 With reference to Figure 1, 49 g of maleic anhydride (1) and 43 g of vinyl acetate (2) were admixed with 300 cm³ of toluene (3) in the mixer tank (D1). In this way, a charge transfer complex, confirmed by the ¹H-NMR spettroscopy, was obtained, wherein both maleic and vinyl units were present in equimolar amounts. A second tank (D2) was fed with a solution (5) consisting of 43 g of pure vinyl acetate (without maleic anhydride), in 80 g of toluene. The content of the tank (D1) was then fed continuously to a reactor (R), and kept at a constant temperature of 110°C. At the same time 21.4 g of a 6.3% b.w. solution (4) of azobis-isobutyronitrile in toluene and the solution (5) coming from tank (D2), carefully keeping the ratios at a constant level. After 1 h, the continuous feeding of the reactants was completed; the reactor was kept, under vigorous stirring, at 110°C for one further hour; thereafter, the copolymer suspension was cooled and discharged. After filtration, washing and drying, 133.8 g of copolymer (Mw = 59 400; Mn = 13 500) were obtained; the copolymer showed a rather regular structure (according to ¹H-NMR analysis), showing one mol of maleic anhydride alternated with 2 mols of vinyl acetate. EXAMPLE 5 This example was carried out in a plant including a pre-mixer for maleic anhydride and vinyl acetate (in the presence of toluene), metering pumps, a container for the catalyst solution and a stirred reactor (provided with jacket and automatic outlet). 824 g/h of a solution containing 11.9% b.w. of maleic anhydride and 10.5% of vinyl acetate, as well as a solution of azobis-isobutyronitrile (in toluene) were continuously fed into the plant so that the feed amount corresponded to 1% b.w. of the overall monomers. At the beginning, the reactor was heated at 110°C, by means of a thermal fluid flowing in the jacket; thereafter, the polymerization heat was removed by reflux condensation of toluene; the residence time, calculated on the overall monomers, was about 5 hours. The suspension of the copolymer was continuously discharged; thereafter it was filtered off and the solid was washed and dried. A powder copolymer was obtained, having Mw = 35,200 and Mn = 10,400. A portion of this copolymer was transesterified with methanol (according to example 10). EXAMPLE 6 30 g of copolymer, prepared according to example 1, and 100 g of anhydrous methanol were introduced into a reactor equipped with stirrer, thermometer and reflux condenser. The whole was heated at the boiling point (approximately 68°C) and the reflux was maintained for 2 hours. Thereafter, 100 cm³ of distilled water were added, while heating under reflux conditions for one further hour. The excess of methyl alcohol was then distilled off; after cooling, the mixture was neutralized with aqueous NaOH (48% b.w.). The final product, diluted to 1% concentration, had a pH = 8.14. Data and results are reported in Table I. EXAMPLES 7, 8, 9 AND 10 Following the pathway of the preceding example, the copolymers (powdery) obtained according to examples 2, 3, 4 and 5 were subjected to a transesterification reaction with methyl alcohol, thus obtaining aqueous solutions of partially transesterified copolymers, which were characterized, as were the non-transesterified copolymers. More particularly, the copolymers obtained according to examples 1, 2, 3, 4 and 5, dissolved into an alkaline solution, and the corresponding copolymers treated according to the transesterification reaction, were characterized, ie the complexing capacity, calcium binding capacity, threshold inhibition and dispersing capacity were determined; the results are reported in Table I. EXAMPLE 11 30 g of the (dry) copolymer obtained according to example 4, were fed into a reactor provided with stirrer, thermometer and reflux condenser; at the same time, 44.85 g of sodium hydroxide (48%) and 110 g of deionized water were fed into the reactor. The reactor was fluxed with nitrogen and heated to boiling for 2 hours under vigorous stirring. A gradual dissolution of the copolymer was obtained and completed within the fixed time (2 h), while an intense yellow coloration was registered. The solution was then cooled, partially decolored, using 2% b.w. of hydrogen peroxide (33% b.w.) and discharged. This solution contained about 17.6% b.w. of hydrolized copolymer (containing maleic acid and vinyl alcohol units) and 7.1% b.w. of sodium acetate. The separation of sodium acetate proved almost impossible by the generally used techniques. Furthermore, the final solution had a disagreeable odour because of partial degradation. The resulting colored solution, when analyzed by GPC, showed a Mw = 46,750 and a Mn = 12,000; these values correspond to a polydispersity ratio equal to 3.8. Data and results are reported in Table I. EXAMPLE 12 A powder detergent, not containing sodium tripolyphosphate and having the following b.w. composition: - Alkylbenzenesulfonic acid sodium salt (LAS) 7.0% - C₁₃-C₁₅ alcohols, ethoxylated with 7 mols of EO 5.0% - Soap 2.0% - Zeolite 4A 27.0% - Sodium carbonate 10.0% - Carboxymethylcellulose 1.0% - Proteolytic enzyme 0.4% - Copolymer (as from Example 10) 4.0% - Sodium sulfate 18.0% - Sodium perborate (tetrahydrate) 20.0% - Sodium disilicate 3.0% - Water 2.6% was used for a washing test in a washing machine at 60°C and 90°C, measuring the washing effect and the incrustations on the fabric after 5,10 and 15 consecutive washings, respectively. The whiteness index obtained with the above reported formulation was similar to the one obtained with a detergent containing no copolymer at all, 10% b.w. of sodium tripolyphosphate and 22% b.w. of Zeolite 4A, namely better than the whiteness index of a formulation free from TPF and copolymer. The ashes (ash amount) after 15 repeated washings (0.75% b.w.), were of the same order as the ones of the formulations containing 10% b.w. of TPF and no copolymer. The amount of ashes after 15 repeated washings using the formulation not containing TPF nor copolymer was higher (more than 1% b.w.). EXAMPLE 13 (Boiler scale test) The anti-scaling effect of the copolymers according to examples 6, 7, 8, 9 and 10 was verified using laboratory experimental apparatus, by turbidimetric determinations taking into account shape and size of the crystals. The inhibition of precipitation and the deposition of solids in non-scaling form was compared with a water which did not contain the transesterified copolymer (a similar test is described also in USP 2,723,956).

Claims: A process for the manufacture of a transesterified copolymer of maleic anhydride in which a copolymer of maleic anhydride and vinyl acetate is prepared, and the thus pre-formed copolymer is then at least partially transesterified, characterised in that the degree of transesterification is from 10 to 80%. A process according to claim 1 wherein an equimolar adduct of maleic anhydride and vinyl acetate is polymerised to form the copolymer. A process according to claim 2 wherein the process is continuous. A process according to claim 2 wherein the process comprises two distinct steps. A process according to any of claims 2 to 4, preferably claim 4, wherein the pre-formed copolymer further comprises a termonomer. A process according to claim 5 wherein the termonomer is mono-unsaturated and is preferably selected from acrylic acid, methacrylic acid, methyl acrylate, butyl acrylate, ethyl acrylate, hydroxyethyl acrylate, itaconic acid, methyl-vinyl ether and vinyl acetate. A process according to claim 6 wherein the amount of termonomer is between 0.05 and 1 mol per mol of maleic anhydride. A process according to any preceding claim wherein the degree of transesterification is from 15 to 50%. A process according to any preceding claim wherein the transesterification temperature is between 50° and 150°C, and preferably between 65° and 120°C. A process according to any preceding claim wherein the transesterification is with an aliphatic or cycloaliphatic alcohol, preferably selected from the saturated aliphatic alcohols containing from 1 to 4 C atoms. A process according to claim 10, wherein said alcohol is methanol. A process according to any preceding claim wherein the transesterified copolymer formed has a weight average molecular weight (Mw) from 1000 to 100,000 and preferably from 2000 to 50,000, and a polydispersity ratio from 2 to 5. A process according to any preceding claim wherein the pre-formed copolymer is prepared by polymerisation carried out between room temperature and 150°C (preferably between 50° and 120°C) with the monomers in the liquid phase, and preferably in a diluent which is preferably an organic liquid selected from aliphatic ketones, aromatic hydrocarbons, cycloaliphatic hydrocarbons, halogenated aromatic hydrocarbons, halogenated aliphatic hydrocarbons and mixtures thereof. A process according to any preceding claim wherein the polymerisation takes place in the presence of a radical initiator selected from acyl peroxides, preferably benzoyl and/or lauroyl peroxide; peresters; dialkyl-peroxides; peroxy-carbonates (percarbonates); hydro-peroxides; azoderivatives, preferably azo-bis-isobutyronitrile; and mixtures thereof. A process according to claim 14 wherein the amount of radical initiator is between 0.05 and 5% b.w. preferably between 0.5 and 2.5% of the overall monomers. A transesterified copolymer of maleic anhydride obtainable by a process as defined in any preceding claim. A detergent formulation comprising a transesterified copolymer as defined in claim 16. A detergent formulation according to claim 17 wherein the amount of copolymer is from 0.5 to 15% and preferably between 1 and 8% by weight of the formulation. Use of a transesterified copolymer as defined in claim 16 to inhibit the formation of scale and to remove already formed scales. Use of a transesterified copolymer according to claim 19, wherein the amount of copolymer is from 0.1 to 1,000 ppm and preferably from 1 to 100 ppm of the liquid to which it is added.

Inventors: COLOMBO PAOLO, MURATORI GIUSEPPE, TROGLIA CLAUDIO, VERZELLINO SANTINA ROSANNA, COLOMBO, PAOLO, MURATORI, GIUSEPPE, TROGLIA, CLAUDIO, VERZELLINO, SANTINA ROSANNA
Applicants: ENICHEM AUGUSTA IND, ENICHEM AUGUSTA INDUSTRIALE S.R.L.
Application year: 1990
Main classification: C08F8
IPC codes: C08F8, C11D3