WO2006094556A1

WO2006094556A1 - Polyelectrolytes based on diquaternary di-ammonium monomers

Info

Publication number: WO2006094556A1
Application number: PCT/EP2005/051060
Authority: WO
Inventors: David Hunkeler; Ivan Vanden Eynde; Piet Vanneste; Sabine Eeckhaoudt
Original assignee: Taminco N.V.; Aqua+Tech Specialties S.A.
Priority date: 2005-03-09
Filing date: 2005-03-09
Publication date: 2006-09-14

Abstract

The invention describes novel polyelectrolytes obtained by the polymerization of diquaternary di-ammonium monomers, preferably with high purity and in powder form, with co-monomers. The polyelectrolyte are either linear and have an intrinsic viscosity, measured at 20 °C in 0.05 M NaCl, higher than 8 dug and a charge density higher than 90% or the monomer composition comprises at least one branching agent so that a branched polyelectrolyte results having preferably an intrinsic viscosity, measured at 20 °C in 0.05 M, higher than 7 dug, preferably higher than 8 dug, and a charge density higher than 30%, preferably higher than 50% and more preferably higher than 90%.

Description

" Polvelectrolytes based on diquaternary di-ammonium monomers"

FIELD OF THE INVENTION

The present invention relates to concentrated formulations of linear and branched, high molar mass and/or highly charged polyelectrolytes based on diquaternary di-ammonium monomers, to their preparation and to their application in solid-liquid separation processes. BACKGROUND OF THE INVENTION

A number of polymerizable cationic monomers, particularly polymerizable cationic acrylic ester monomers, are well known in the art and are finding substantial commercial use for the production of water-soluble polyelectrolytes (charged polymers). Such polymerizable cationic monomers are used for the production of homopolymers and more especially for the production of co-polymers with, such co-monomers as acrylamide, acrylic esters (e.g. ethyl acrylate or methyl methacrylate), styrene, vinyl acetate, and vinyl chloride. As examples of commercially available cationic acrylate and methacrylate monomers may be mentioned the quatemized products of dimethylaminoethyl acrylate and methacrylate.

The commercially available, polymerizable, cationic acrylic ester monomers described above are characterized by the presence of a single quaternary ammonium group in the molecule. Consequently, particularly in the production of co-polymers where a high degree of cationic functionality is desired in the polymer backbone, it is necessary to use a high proportion of these cationic monomers to its co-monomer. While such high relative proportion of these cationic monomers is desirable to increase the cationic functionality in the polymer backbone, it may at the same time dilute or adversely affect other desirable properties contributed by the co-monomer to the resultant copolymer. To obtain high performance flocculants, cationic monomers are usually polymerized with acrylamide, a non-ionic monomer which permits the formation of high molecular weight polymers (as indicated by a parameter such as intrinsic viscosity). Thus far, the properties desired in a polyelectrolyte for solid-liquid separations, namely high molecular weight and high degree of cationicity, have been irreconcilable. Recently, improved synthesis processes have led to the production of diquaternary di-ammonium monomers at improved yield levels, in the form of aqueous solutions (65-75% aqueous solutions BDMAPA-2BzCl). (Ref. 3, 8, 9, 10).

These diquaternary di-ammonium monomers, when used in the same molar proportions as the well known commercial cationic monomers mentioned above, can impart a higher degree of cationic functionality to polymers produced there from and, in the case of co-polymers, the same degree of cationic functionality can be obtained in co-polymers produced by their use in a substantially lower molar proportion.

Water-soluble polymers based on the above described diquaternary di- ammonium monomers were described in Ref 3. We have noted that the techniques disclosed herein do not allow the synthesis of polyelectrolytes with increased cationic functionalities through the incorporation of elevated diquaternary di-ammonium monomers in the synthesis process. We have found that the monomer synthesis procedures of the prior art result in diluted aqueous formulations containing impurities such as acids, alcohols and alkylhalogenides, as well as uncompletely quaternised di-ammonium monomers (formula HI). These findings constrain the use of the diquaternary di-ammonium monomer to polymerization processes in which high cationic functionalities and formulations with high polymer solid levels are not an aim. Products with low solid levels would highly limit the use of the novel polyelectrolytes geographically or restrict their application to very high value added situations. As the present invention is oriented toward solid-liquid separations and flocculation, this is not desired. It is of importance to be able to a make a range of polyelectrolytes with varying degrees of cationic functionalities and high molar mass to address solid-liquid separation issues such as flocculation in water treatment processes. The preparation of high molar mass polyelectrolytes requires the availability of diquaternary di-ammonium monomer formulations that are substantially free of impurities, as impurities can act as undesired transfer agents, reducing the molar mass. This topic is well researched for commercially available monomers containing a single quaternary ammonium group in the molecule.(Ref. 11, 12)

An object of the present invention is to provide new (co)polymers, based on these diquaternary di-ammonium monomers, which do exhibit good flocculant properties, similar to the polymers based on monoquaternary ammonium salts found in commerce today. In this way, an alternative to the known monoquaternary ammonium salts-based flocculants is available so that, based on a particular need (e.g. for the different requirements in solid-liquid separations), a larger range of flocculants is available to select the one with the best performance for a given water-treatment situation.

Additionally there is a need for polymer formulations with relatively high solid contents. Though acrylamide is also available in crystalline form, the preferred form is the aqueous solution to avoid dust exposure to a toxic, and presumed carcinogenic, chemical. Moreover, the prior art processes for preparing co-polymers based on diquaternary di-ammonium monomers need relatively low solid contents to avoid coagulum and gel formation and to keep the inverse emulsion or suspension stable, especially in the case of higher molecular weights and/or higher charge densities.

To someone skilled in the art, the need to be able to have polyelectrolytes in powdered form would be obvious, as it provides handling and transport advantages, and a lower risk in the case of spillage. To the inventors' knowledge there are no existing technologies for the preparation of branched powders based - A -

on diquaternary di-ammonium monomers, via inverse-suspension polymerization (Ref 1). For mono-quaternary ammonium monomers, it is known that the control of branching is difficult. When attempting to prepare dry structured (co-)polymers it has been found that problems arise due to the solubility being lost or reduced.

Such polyelectrolytes, which are ultimately applied in aqueous solutions, would due to their higher charge density and higher concentration in water, be expected to be more effective in typical applications, such as solid-liquid separations.

SUMMARY OF THE INVENTION

The invention describes novel polyelectrolytes obtained by the polymerization of diquaternary di-ammonium monomers, preferably with high purity and in powder form, with co-monomers. The polyelectrolyte are either linear and have an intrinsic viscosity, measured at 20 ⁰C in 0.05 M NaCl, higher than 8 dl/g and a charge density higher than 90% or the monomer composition comprises at least one branching agent so that a branched polyelectrolyte results having preferably an intrinsic viscosity, measured at 20 ⁰C in 0.05M, higher than 7 dl/g, preferably higher than 8 dl/g, and a charge density higher than 30%, preferably higher than 50% and more preferably higher than 90%. The molar mass of the polyelectrolytes is preferably as high as possible. In a preferred embodiment of the invention, the intrinsic viscosity of the polyelectrolytes is therefore even higher than 10 dl/g, preferably higher than 15 dl/g and more preferably higher than 20 dl/g. The polyelectrolytes are prepared from a monomer composition comprising, per 100 parts by moles of monomers:

1) from 15 to 100 parts by moles of at least one (meth)acryl di-ammonium salt of formula (I)

(I) wherein R represents hydrogen or methyl, each R , independently, represents an alkyl comprising from 1 to 4 carbon atoms, each R³, independently, represents an alkyl or an aralkyl and each X^", independently, represents an anion; and 2) from 0 to 85 parts by moles of one or more other charged or uncharged co- monomers, including optionally at least one chain branching agent. The polyelectrolytes are preferably prepared by a heterophase water-in-oil process from this monomer composition. Moreover, R² is preferably methyl while R³ is preferably methyl or benzyl, more preferably methyl.

The diquaternary di-ammonium monomers are preferably DIPOLE-A (full chemical name l,3-bis(trimethylammonium)-2-propyl acrylate chloride with a molar mass of 301.26 g/mol) and DIPOLE-M (full chemical name 1,3- bis(trimethylammonium)-2-propyl methacrylate chloride with a molar mass of 315.29 g/mol).

In a preferred embodiment, the monomer composition comprises between 1 and 85 parts by moles of at least one water-soluble co-monomer of formula (II)

CH₂=CR¹ CO-NR²R³ wherein R¹ represents hydrogen or methyl and R² and R³ , which may be identical or different, each independently represent hydrogen or an alkyl comprising 1 to 5 carbon atoms, optionally comprising one or more hydroxyl groups, or the monomer composition comprises between 1 and 85 parts by moles of at least one water-soluble co-monomer selected from the group consisting of acrylamide, methacrylamide, N-methylolacrylamide, N-vinylmethylacetamide, N- vi ny lmethy lformamide, di alky lami n oalky 1 (meth) aery lamide, sulphomethylated acrylamide, vinyl acetate, N-vinylpyrrolidone, methyl (meth)acrylate, styrene, dialkylaminoalkyl(meth)acrylate, 1.3- bis(dimethylamino)-2-propyl (meth)acrylate, l,3-bis(trimethylammonium)-2- propyl (meth) acrylate chloride, trimethylaminoethyl (meth) acrylate-methyl, diallyldimethylammonium chloride,

(meth)acrylamidopropyltrimethylammonium chloride, (meth)acrylic acid, sodium (meth)acrylate, itaconic acid, sodium itaconate, 2-acrylamide 2-methyl propane sulphonate, sulphopropyl(meth)acrylate. The preferred co-monomer is acrylamide.

For branched polyelectrolytes, the chain branching agent is preferably selected from the group consisting of methylene-bis-acrylamide, divinyl benzene, diethylene glycol diacrylate, propylene glycol dimethacrylate, diallyl acrylate, diallyl fumarate, trimethyloxy propane triacrylate, the monomer composition preferably comprising methylene-bis-acrylamide. The preferred chain branching agent is methylene-bis-acrylamide (MBA).

The diquaternary di-ammonium monomer allows one to reduce the amount of charged monomers to, roughly, half relative to monoquaternary monomer-based polymers so that, when other co-monomers are used, these can be used in a larger amount. The diquaternary di-ammonium monomer is preferably used in its high purity, crystalline powder form. It preferably contains, per kg of the (meth)acryl di-ammonium salt of formula (I), less than 20 g, preferably less than 5 g, and more preferably less than 2 g of impurities which may stop the chain elongation growth reducing the average chain length during the polymerisation reaction. This monomer is advantageously dissolved in an aqueous acrylamide solution, so that water levels can be kept at a minimum and high solid levels can be obtained.

Polyelectrolytes prepared by inverse-emulsion result in polymers with a charge of 0.1 to 6.3 mEq, preferably 1 to 6 mEq and most preferably between 2 and 5 mEq. Said polyelectrolytes are prepared in a high molar mass form, with an intrinsic viscosity of 10 to 25 dl/g, preferably 12 to 25 dl/g and most preferably between 12 and 20 dl/g. Adjustment of the HLB of the surfactant or surfactant blend and the concentration used provided the stability needed to enable the preparation of polyelectrolytes of high molar mass and high charge levels. It also allows the incorporation of branching-agents.

In the present specification a polymerization of cationic monomers at high cationic charge, in inverse-emulsion, at high solids levels (40% by weight) is described. The final HLB of the blend, for optimal stability in a cationic inverse-emulsion, was approximately 8.0, and more generally between 7.8 and 8.2. The total surfactant level for inverse-emulsions is typically in the range of 1.5-5 wt% of the overall formulation, preferably 2-4 wt%, and more preferably 2.5 to 3.5 wt%.

Polyelectrolytes prepared by inverse-suspension incorporating the use of polymeric surfactants produced large microbeads (ca 100 micrometers versus 0.1 to 0.2 micrometers, on average, for inverse-emulsions based on fatty acid esters). This can be exploited if the polyelectrolyte is required in powdered form, since the larger beads can be easily settled, filtered and dried.

Branched powders based on diquaternary di-ammonium monomers obtained via inverse-suspension polymerization are obtained for the first time. Flocculation with highly charged polyelectrolytes based on diquaternary di-ammonium monomers demonstrates that each diquaternary di-ammonium group can on average replace two mono-quaternary ammonium groups. Furthermore, the dosage of diquaternary-based polymers was, on average, equivalent or slightly below that for the monoquatemary-based polymers (15.1 ppm for the PolarFloc, based on diquaternary monomers, versus 16.0 ppm for the AlpineFloc based on monoquaternary ammonium monomers).

Flocculation with highly charged, linear or branched, polyelectrolytes based on the crystalline powder form of diquaternary di-ammonium monomers can provide a more rapid and extensive dewatering resulting in higher amounts of dry material. The polyelectrolytes can function at a lower dosage than the corresponding polymers based on monoquaternary ammonium monomers.

The invention also provides new methods of flocculating solids from an aqueous composition, for increasing the rate of water removal, for increasing the dry material levels, for improving the filtrate clarity during the dewatering of wet sludges and for increasing the decantation rate.

DETAILED DESCRIPTION OF THE INVENTION

Definitions of Terms As used herein, the following abbreviations and terms shall have the following meanings:

Initiator

V65, an initiator from Wako, Germany

Monomers Acrylamide, a non-ionic monomer, from Ciba UK, and Cytec UK

MBA, methylene-bis-acrylamide, a difunctional non-ionic monomer supplied by

Fischer, Switzerland and Cytec, UK

Oils

Exoll DlOO, a mineral oil, supplied by Esso, Switzerland ISOPAR-M, a mineral oil, supplied by Esso Switzerland

Surfactants

Montane 80 (sorbitan monooleate), from Seppic, France

Montanox 85 (polyoxyethylene sorbitan trioleate),

Rolfor TR/8/L wetting agent Acids

EDTA ethylenediaminetetraacetic acid, supplied by Merck, Switzerland

Adipic acid from BASF, Germany

Lactic acid from Reactolab, Switzerland

Salts NaBrO₃, sodium bromate, supplied by Merck, Switzerland Na MBS, sodium metabi sulfite, supplied by Schweizerhall, Basel, Switzerland

Solvents

Xylene, supplied by Reactolab, Switzerland

Inhibitor MEHQ, p-methoxyphenol

Abbreviations (General)

IV intrinsic viscosity

RPM rotations per minute

HLB Hydrophilic-Lipophilic Balance Abbreviations (Monomers)

DMAEA for dimethylaminoethyl acrylate

DMAEM for dimethylaminoethyl methacrylate

DMAEA-CH3C1 for dimethylaminoethyl acrylate, methyl chloride quaternary salt DMAEM-CH3C1 for dimethylaminoethyl methacrylate, methyl chloride quaternary salt

BDMAPA for 1 ,3-bis(dimethylamino)-2-propyl acrylate

BDMAPMA for 1 ,3-bis(dimethylamino)-2-propyl methacrylate

Dipole-A for l,3-bis(trimethylammonium)-2-propyl acrylate chloride or BDMAPA.2MeCl

Dipole-M for l,3-bis(trimethylammonium)-2-propy] methacrylate chloride or BDMAPMA.2MeCl

Abbreviations (Polymer)

The polymer codes can be explained as follows: - AlpineFloc™ refers to a polymer based on DMAEA-CH3C1 or

DMAEM-CH3C1

- PolarFloc-A and PolarFloc-M refer to a polymer based on Dipole-A and Dipole-M respectively.

- The first letter of the code provides the weight fraction of charged monomers (e.g. the "E" E/Q indicates a polymer with 50% charged monomers, in this case, 50 wt% of the monomer which is based on di- quaternary ammoniums).

- The second letter in the code provides the charge density (e.g. the "Q" in E/Q indicates a polymer with a charge density of 100% (or higher), calculated from the 50% by mass of cationic monomer, times two charges per monomer unit).

For the AlpineFloc™ there is only one letter in the code, as the weight fraction of charged monomer is the same as the charge density.

- The number in the code indicates the molar mass (e.g. E/Q 1 implies high molar mass)

- The number of "+" at the suffix of the code indicates the branching level (+: 4 ppm of difunctional monomer, ++: 8 ppm of difunctional monomer) Polymers can be prepared over a range of molar masses. Typically polymers, posses a distribution of molar masses and, hence, are represented by an average molar mass or a viscosity. As the average molar mass increases, so too does the viscosity of the polymer dissolved in a solvent. Viscosity can be expressed as the viscosity, generally measured under shear, or, more commonly, if one seeks to represent the molar mass via viscosity, by the "intrinsic viscosity". Intrinsic viscosity is measured in a thermostated glass viscometer, where the flow times of the solution are measured. The widely standardized method involves subtracting the flow time of the polymer, at a given concentration, in solution, (tp) from the solvent from which the solution is made (to). One obtains the "reduced viscosity" by subtracting the solvent time from the polymer solution time, i.e. tp-to. A relative viscosity can then be obtained by dividing the reduced viscosity by the solvent time, i.e. (tp-to)/to. The "specific viscosity" can then be calculated by dividing the relative viscosity by the concentration. If one plots the specific viscosity as a function of concentration, and extrapolates to zero concentration, then the intercept of the y-axis (i.e. specific viscosity at zero concentration) yields the "intrinsic viscosity". The intrinsic viscosity is usually expressed in ml/g or dl/g. PolarFloc-M G/E 1+ yielded an intrinsic viscosity, in 0.05 M NaCl, of 8.06 dl/g while PolarFloc-M E/Q 1 ++ had an intrinsic viscosity, in 0.05 M NaCl, of 10.58 dl/g.

Polymers also posses distributions with respect to other parameters such as a distribution of monomer composition. This, both along the chain (referred, commonly, as the sequence length distribution) as well as between chains (the copolymer composition distribution). Should the polymer be branched, or nonlinear, then it can also posses an inter-molecular branching distribution.

Molecular weight can also be inferred or measured based on other indirect or direct methods, including size-exclusion chromatography, light scattering and analytical ultracentrifugation. In the latter a solution is spun at, generally quite high speeds, and the equilibrium or synthetic boundary profiles are measured. An averaged sedimentation coefficient, typically expressed in svedbergs, is used to represent the molar mass distribution. The sedimentation coefficient distribution can also be calculated. Generally, for polyelectrolytes, higher sedimentation coefficients are desirable, in particular higher than 3 svedbergs, with those above 5 svedbergs being the most preferred.

Solutions of polyelectrolytes (charged polymers) are typically prepared in polar solvents such as dimethylformamide (DMF), dimethylsulfoxide (DMSO) and most commonly, water or saline solutions. When a polyelectrolyte is applied in a solid-liquid separation it requires a very high molar mass when inverted in an aqueous solution. Molar masses are typically above one million daltons, more typically above 3 million daltons and very often above 10 million daltons and as high as 30 million daltons. As polymer solutions would have viscosities approximately one million times that of water they would resemble a highly viscous gel and would no longer be processable. The majority of polyelectrolytes, destined for use in solid-liquid separations is therefore synthesized in heterophase, water-in-oil, processes, so as to permit locally elevated viscosities, while maintaining a dispersion with pourable or pumpable properties, generally with a bulk viscosity on the order of 1000 cP. Heterophase water-in-oil processes typically involve the dispersion of an aqueous monomer mixture in a continuous, generally aliphatic, organic phase.

The stabilization of the water-in-oil interface is carried out with a variety of, generally blended, surfactants. These can be small, natural molecules (e.g. fatty acid esters), oligomeric in nature (e.g. ethoxylated fatty acid esters) or polymeric. Heterophase water-in-oil systems are kinetically stable, implying that the emulsion settles with time. They are prepared at surfactant levels on the order of 0.1 to 5%. "Inverse-suspensions" settle over a matter of hours or days and are prepared at the low end of such a concentration range, in particular at surfactants levels of between 0.1 and 1.5 wt%, preferably between 0.1 and 1 wt%. "Inverse-emulsions" have stabilities in the months and are prepared at the high end of the concentration range, in particular at surfactants levels of between 1.5 and 5 wt%, preferably between 2 and 4 wt%.

The ultimate molar mass of a polyelectrolyte is controlled via the addition of a variety of chain- transfer agents, as well as by the use of chain- branching agents. Chain-transfer agents are molecules used in free-radical polymerization, which will react with a polymer radical forming a dead polymer and a new radical. Chain-branching agents are multifunctional monomers containing more than one reactive group. For a radical polymerization this implies the presence of more than one residual, unsaturated, carbon-carbon double bound. The chain-branching agent may be added continually or discretely, as described in the prior art (Ref 4-6).

Typical inverse-emulsions are prepared either using blends of surfactants, or using polymeric stabilizers, either alone or in combination with said surfactants. It is generally accepted that a surfactant represents a low molar mass molecule, generally of a few hundred Daltons (i.e. lower than 1000 Daltons), whereas a polymeric stabilizer is a long-chain polymer with molar masses in the thousands (i.e. higher than 1000 Daltons), often tens of thousands, and occasionally hundreds of thousands of Daltons. Especially when polymers having high molecular weights with higher solid contents are required, particularly when preparing inverse-suspensions which are further converted into dry powders, more particularly dry structured powders, use is preferably made of one or more polymeric stabilizers. The stabilizing agent preferably comprises at least one stabilizing polymer derived from a hydrophobic mixture of methacrylate monomers having the following formula (A):

O Il

(A) CH₂=C-C-OR₁

CH₃ wherein Ri is an alkyl group from 14 to 20 carbon atoms; and a hydrophilic monomer component having the following formula (B)

O Il

(B) CH₂=C-C-OH

R₂ wherein R₂ is CH3 or H, and wherein the stabilizing agent has a number average molecular weight that is from about 500 to 50,000 g/mol. The stabilizing polymer is more preferably derived from said hydrophobic mixture wherein the methacrylate monomers are about 90 to 98 % methacrylates having alkyl groups that are 16 to 18 carbon atoms in length and wherein component (B) is comprised of a mixture of acrylic acid and methacrylic acid.

When surfactants, and/or stabilizers, are blended, the average properties of the mixture are generally calculated by the "Hydrophilic-Lipophilic Balance". The "HLB" of a mixture is the average of the individual HLBs for surfactants or stabilizers. For some, pure, chemical species, the HLB can be precisely calculated based on the molecular composition, whereas for other, particularly polymeric, systems, which are, inherently blends of several distributions, HLB is approximate. The average HLB is calculated either according to the weight, or alternatively mole, fraction of the individual surfactants and stabilizers. There is debate in the scientific literature as to if weight-averaging or mol-averaging is more appropriate. In this disclosure we have used weight averaging.

Surfactants can have HLBs between 0 and 20. In general, molecules with lower HLB (3 to 6), such as fatty acid esters (e.g. sorbitan monooleate has an HLB of 4.3) are used in combination with molecules with an HLB above 10 to prepare a blend with an average HLB in the range of 4-9. Examples of high

HLB surfactants include polyoxyethylene sorbitan trioleate, with an HLB of 11.

The optimal HLB for anionically charged polymers (e.g. for polyacrylamide-co-acrylic acid) would be between 7 and 9. For inverse- emulsion polymerizations of cationic monomers, the HLB of the system is typically 4-6. This has been shown to be true for inverse-emulsions based on monoquaternary monomers (Ref 4-6). Also for inverse-emulsions based on di- quaternary di-ammonium monomers a surfactant system was used in Ref 3 having an HLB below 6, in particular an HLB of about 5.42 in Examples 1 and 2.

According to the invention it has been found therefore quite surprisingly that the final HLB of the blend, for optimal stability in a cationic inverse- emulsion, i.e. for enabling to achieve high molar masses, high charge densities and/or high polymeric solid contents, was higher than 6 and preferably higher than 7. For an optimal stability the HLB of the surfactant or surfactant blend was more particularly approximately 8.0, and more generally between 7.8 and 8.2.

When preparing polyelectrolyte emulsions or suspensions having a relatively high solid content (i.e. the most commercially relevant), in particular a solid content higher than 25 wt%, preferably higher than 35 wt% or even higher than 40 wt%, and a relatively high charge density, in particular a charge density higher than 90%, preferably higher than 100% or even higher than 110 or 120%, the surfactant or surfactant blend has preferably an HLB higher than 6 and more preferably higher than 7 to avoid stability problems.

The total surfactant level for inverse-emulsions is typically in the range of 2-4 wt% of the overall formulation, more typically 2.5 to 3.5 wt%. Inverse-emulsions can be prepared at solids levels of 45% and below. Above 45%, the water-in-oil polymerizable phase will quite often invert, with the formation of a water-based, lower layer, gel, increasingly possible as the solids levels rises. Higher solid level final products, which can exceed 50%, are generally prepared by post-processing an inverse-emulsion to remove some of the water. Therefore, a process wherein the minimum of water is added at the outset, provides advantages. In a preferred embodiment, use is therefore made in the process according to the invention of the minimum amount of water required to dissolve the (co-)monomers, or an amount of water which is at the most 10% higher, or preferably at the most only 5% higher than this minimum amount of water. At the extreme, all excess water, other than that which is in the raw material products (e.g. the acrylamide solution) could be eliminated. It has been found that this is possible by dissolving a solid monomer containing product, for example a cationic monomer, directly in the acrylamide solution (or in an aqueous solution of another co-monomer).

Preferred Embodiments

The present invention will now be described more fully, hereinafter with reference to the accompanying examples, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

Monomer synthesis and selection

The present invention describes the preparation of polyelectrolytes based on diquaternary di-ammonium monomers which may combine a relatively high charge density with a relatively high molar mass (intrinsic viscosity) and/or which may be branched. The preferred diquaternary di-ammonium monomers are DlPOLE-A and DIPOLE-M. Prior art methods for synthesis of these diquaternary monomers result in mixtures of mono- and di-quaternary monomers with more significant levels of impurities. The diquaternary di-ammonium monomers preferred for the present invention are unique in that they are available in crystalline powder form, with a content of over 98 %, typically 99.5 %, with limited amounts of monoquaternary byproducts and impurities.

The diquaternary di-ammonium powder can be dissolved in water to make up a 50% aqueous solution (solubility limit of Dipole-M in water is around 50%). This solution can be stabilized with, for instance, p-methoxypenol (MEHQ), to inhibit polymerization. A disadvantage of such method is that by dissolving the diquaternary di-ammonium powder in water, the solid content of the inverse-emulsion or suspension is reduced. The powder form does not need to be stabilized, with for instance MEHQ, so that this polymerization inhibitor does not have to be removed prior to the use of the monomer. Surprisingly, it has now been found that the diquaternary di-ammonium monomer powder dissolved faster in a solution containing already a co- monomer, such as in particular in a 50% aqueous acrylamide solution, than it does in water. This offers the possibility to achieve polyelectrolyte formulations with increased charge levels with high solid levels. Dipole-A and Dipole-M are obtained from the quaternization of

BDMAPA and BDMAPMA respectively, with methylchloride.

The diquaternary di-ammonium monomers preferred for the present invention can be made with a process that provides the selective manufacture of (meth)acrylate di-ammonium salts. Such a process is described in the co-pending PCT application PCT/EP2004/052056 and in the European patent application No. 1512676, published on March 9, 2005, which are hereby incorportated by reference. According to these patent applications, the process for the manufacture of a (meth)acrylate di-ammonium salt of formula (I)

(I) wherein Rl represents hydrogen or methyl, each R^, independently, represents an alkyl comprising from 1 to 4 carbon atoms, each R^, independently, represents an alkyl or an aralkyl and each X^" , independently, represents an anion, comprises

(a) the reaction of the di-amino-(meth)acrylate of formula (IV)

with preferably more than 2 equivalents of at least one alkyl or aralkyl compound of formula R^X in an organic solvent containing at most 5000 ppm of water and wherein the di-ammonium salt of formula (1) has a solubility at 25 ⁰C of less than 1 g/100 g of solvent and wherein the solubility of the corresponding amino-(meth)acrylate ammonium salt of formula (III)

(HI

has a solubility at 25 ⁰C of at least 20 g/100 g of solvent ; and (b) the separation of the compound of formula (I) from the reaction mixture without dissolving it in water, the compound of formula (I) being separated from the reaction mixture in the form of a solid monomer product comprising the compound of formula (I) and, per mole of this compound, less than 0.1 mole, preferably less than 0.05 mole and more preferably less than 0.01 mole of the compound of formula (III).

The solid monomer product prepared in this way moreover comprises, per kilogram of the compound of formula (I) less than 20 g, preferably less than 5 g, and more preferably less than 2 g of impurities which may stop the chain elongation growth reducing the average chain length during the polymerisation reaction.

In the same process, the organic solvent used in step (a) preferably contains at most 1000 ppm of water. The organic solvent used is preferably a solvent wherein the solubility of the di-ammonium salt of formula (I) has a solubility at 25°C of less than 0.5 g/100 g of solvent.

In the same process, the solvent used in step (a) is usually an aprotic dipolar solvent; preferably acetone, methylethylketone, ethylacetate, nitromethane, acetonitrile or mixtures thereof. Particularly preferred is acetonitrile. The reaction of step (a) is preferably carried out in an amount of between 500 and 5000 g of solvent per mole of the di-amino (meth)acrylate of formula (IV) added to the solvent. In this process , step (a) is preferably carried out at a temperature ranging from 40 to 100 ⁰C, most preferably from 70 to 90 ⁰C. The process is preferably conducted at autogenic pressure in a closed reactor.

In this process, step (a) is advantageously conducted with a molar ratio of the allcyl or aralkyl compound of formula R^X to the di-amino-(meth)acrylate of formula (IV) higher than 2, most preferably of at least 2.1. The molar ratio preferably does not exceed 4.5, most preferably it does not exceed 3.

The duration of step (a) is generally from 1 to 100 hours, preferably from 10 to 30 hours. The separation of pure crystalline or solid product containing the

(meth)acrylate di-ammonium salt of formula (I) in step (b) of the process according to the invention may be carried out by any means suitable for a mechanical separation. It is advantageously done by filtration or by centrifugation of the reaction mixture. In an embodiment of the process, the excess of alkyl or aralkyl derivative of formula R^X used in step (a) is separated from the reaction mixture, for example by stripping, before effectuating the separation in step (b). .

The process can be done as batch or continuously. In the latter case, the solid product containing the (meth)acrylate di-ammonium salt of formula (I) formed during step (a) can be separated from the reaction mixture continuously, for example by filtration, decantation or any other mean suitable therefore, and the reaction mixture can then be recycled and used as solvent in a subsequent reaction step (a).

According to another preferred embodiment of the process, the reaction mixture obtained after step (b) is recycled. In this embodiment, it is particularly preferred that the reaction mixture obtained after step (a) is filtered in step (b) in order to separate the solid product containing the (meth)acrylate di-ammonium salt of formula (I) already formed and to recycle the filtrate in a subsequent step (a) in order to continue the reaction. This recycling operation can be repeated several times. The recycling of the filtrate permits to increase even more the yield and the purity of the (meth)acrylate di-ammonium salt of formula (I).

In a variant of the process, both embodiments are combined.

In the process according to the invention, compounds of formula (I), (III) and (IV) wherein R.1 is methyl are especially preferred. hi the process according to the invention, compounds of formula (I), (HI) and (IV) wherein R^ is methyl are especially preferred.

In the process according to the invention, (meth)acrylate di-ammonium salts of formula (I) wherein each Rβ, independently, is an alkyl comprising from 1 to 4 carbon atoms or benzyl, are preferred. Most preferred are compounds wherein each R.3, independently, is methyl or benzyl; especially methyl.

(Meth)acrylate di-ammonium salts of formula (I) wherein both R^ are the same are preferred.

In the process according to the invention, (meth)acrylate di-ammonium salts of formula (I) wherein each X, independently, is an anion selected from halides, especially chloride and bromide, and methylsulfonates are preferred. Especially preferred is chloride.

The process permits to obtain a high yield of the desired (meth)acrylate di-ammonium salts of formula (I). Yields of at least 90, even 99 %, can be obtained, resulting in 99+ pure (meth) aery late di-ammonium salts of formula (I). Almost no side products are formed. In the final product the amount of impurities such as allcylhalogenides, alcohol and acids that could disturb further polymerisation of the product, are very low. The quantity of amino- (meth)acrylate ammonium salt of formula (IE) (relative to the amount of di- ammonium salt of formula (I)) in the final product is very low, usually less than 10 mole %, preferably less than 5 mole %, or even less than 1 mole %.

Moreover, the process permits to obtain the products in pure solid form. In this form the products show high stability and can be stored for long periods without decomposition. Once the solid product is isolated, aqueous solutions and formulations with other monomers can be made as required for the envisaged application.

Co-monomer selection The co-monomers which may be used for the preparation of the polyelectrolytes of this invention are in particular ethylenically unsaturated monomers. The co-monomers can be allyl monomers, though are generally vinyl, preferably acrylic.

Examples of non-ionic co-monomers include, but are not limited to, acrylamide, methacrylamide, N-methylolacrylamide, N-vinylmethylacetamide, N-vinyl methyl formamide, dialkylaminoalkyl(meth)acrylamide, sulphomethylated acrylamide, vinyl acetate, N-vinyl pyrrolidone, methyl (meth)acrylate, styrene, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate and 1.3-bis(dimethylamino)-2-propyl (meth)acrylate. Examples of cationic co-monomers are trimethylaminoethyl acrylate- methyl chloride (TMAEA-CH3C1), trimethylaminoethyl methacrylate-methyl chloride (TMAEM-CH3C1), diallyldimethylammonium chloride, meώacrylarnidopropyltrimethylammonium chloride, and acrylamidopropyltrimethylammonium chloride. Examples of anionic monomers, co-polymerized with the aforementioned diquatemary di-ammonium monomers to form polyampholytes include, for example, (meth)acrylic acid, sodium (meth)acrylate, itaconic acid, sodium itaconate, 2-acrylamide 2-methyl propane sulphonate, sulphopropyl(meth)acrylate

Polymer synthesis

All polymers based on the diquatemary di-ammonium monomers were synthesized via heterophase polymerization techniques: by inverse-emulsion or inverse suspension, either in batch or semi-continuous mode (Ref 4-6). lnverse- emulsion and inverse-suspension polymerization are the preferred embodiment for this invention, though inverse-microemulsion polymerization can also be applied.

The development of a compatible heterophase water-in-oil polymerization process permits the synthesis of high charged polyelectrolytes, at high molar masses, and at high concentrations, otherwise impossible with less pure quaternary monomers. Specifically, cationic polymers with charge densities between 90 to 200 % can be prepared.

The inverse-emulsion polymerization in this invention contains a dispersed aqueous phase containing the polymer of the invention, and a continuous organic phase with limited water miscibility. The percentage of the aqueous phase comprises usually about 40 to 95% of the total weight, preferably 70-80%. The aqueous phase contains the monomers in concentrations usually between 40% and 90%, preferably from 45 to 80%.

The invention can be applied with both solid and liquid forms of (co-)monomers. If one or more of the (co-)monomers is in solution, then the polymerizations can be carried out without any additional water. Should one or more of the (co-)monomers be in solid form, then the polymerizations can be carried out at the solubility limit of the (co-)monomers (in water). The oil used in the organic phase may be any inert aliphatic and/or aromatic liquid which does not interfere in the polymerization reaction. Examples include, but are not limited to, benzene, xylene, toluene, mineral oils, isoparaffinic oils, kerosenes, napthas and mixtures thereof. Preferably the oil phase comprises about 15 to 30% of the total weight of the emulsion. The most stable inverse-emulsions are obtained by balancing the molar volume of the hydrophobic part of the surfactant with that of the oil. Therefore, the most suitable oil for an organic, continuous, phase is a mineral oil with similar properties to sorbitan based fatty acid esters, such as a low aromatic oil with a boiling point in the range of 130 to 250 ⁰C, most preferably between 200 and 240 ⁰C. Typical organic phases are commercially available as, for example, Isopar or Exoll from Exxon as well as Shellsolv, to name just a few. The organic phase typically contains surface-active agents (surfactants). Such surfactants are well known in the art and are used to promote and maintain the stabilization of water-in-oil inverse-emulsions. Typically, surfactants or stabilizers have HLB values from about 2 to 10, once blended, preferably between 5 and 9. For this invention, the optimal HLB is between 6 and 9, more particularly between 7 and 9. Examples of surfactants employed include, but are not limited to, sorbitan esters of fatty acids, alkanolamides, fatty acid glycerides, glycerine esters, as well as ethoxylated versions of the above and any other well know emulsifier, including polymeric surfactants. Syntheses were performed via inverse-emulsion polymerization using blends of surface-active agents so as to adjust the stability of the interface and the final inverse-emulsion. Such blends are specific to the type of diquaternary di-ammonium monomer, and its concentration in the recipe.

The surfactants should be used in amounts not greater than about 5 weight percent of the total emulsion, preferably not greater than 2-4%. The most suitable surfactant blend, for inverse-emulsions based on DlPOLE-A and DIPOLE-M, with or without nonionic monomers, has an HLB of approximately 8.0 at a surfactant level between 2 and 4 wt% of the total recipe, most preferably between 2.3 and 3.9 % of the total recipe. In one embodiment of the invention fatty acid esters and ethoxylated fatty acid esters have been employed. However, someone skilled in the art would recognize that a large number of surface active agents can be employed, with a variety of co- and ter-monomers, as is outlined in the detailed description of the invention. Someone skilled in the art would recognize that, for natural products such as the sorbitan fatty acid esters and ethoxylated sorbitan fatty acid esters, the HLB is lot dependent. Someone skilled in the art would also recognize that the optimal HLB will, depending on the charge density, slightly change by 0.2-0.4 HLB units as one moves from O to 200% charge density if one wished to optimize the water-in-oil system with respect to prevention of oil phase separation. Therefore, the exact ratio of sorbitan fatty acid esters and ethoxylated fatty acid esters could be slightly batch and charge density dependent as an experienced formulator would be aware off.

The emulsion in this invention is preferably created via pre- emulsification in order to form a stable water-in-oil system. Pre-emulsifϊcation, to someone skilled in the art, is a recognized means to homogenize prior to polymerization. It is generally carried out at a specific agitation rate, either to a given viscosity limit or for a fixed period of time. To someone skilled in the art, the types of homogenizers which could be employed would be evident, with emulsification preformed either for a specific time or, more preferably, to a set viscosity, such as 100 to 500 cP, more specifically 200-400 cP.

The polymerization reaction process of this invention can be carried out in the presence of a conventional polymerization initiator. Examples of suitable oil-soluble initiators, the preferred embodiment, include, for example, dibenzoyl peroxide, dilauryl peroxide, tert-butyl peroxide or azo compounds such as 2,2'- azobisisobutyronitrile, dimethyl 2,2'azobisisobutyrate and 2-2'-azobis-(4- methoxy-2,4-dimethylvaleronitrile). Someone skilled in the art would recognize that water soluble initiators, as well as redox based systems, could also be applied. Examples of water-soluble initiators include, for example, 2,2'-azobis- (2-amidinopropane) dihydrochloride, 4,4'-azobis-(4-cyanopentanoic acid) or redox systems such as ammonium persulfate/ferric sulfate.

The polymerization temperature is selected based on the decomposition temperature of the initiator and to avoid, at high temperatures, the cross-linking of the polymers. It may be from about 5 to 99 ⁰C, preferably between 25 and 75 ⁰C and most preferably between 40 and 75 ⁰C. However, it is possible to maintain a low, stable, initial temperature and increase this after a certain conversion, either by raising the temperature or following the adiabatic exotherm, so as to reduce residual monomer. It is also possible, to the same end, to add additional initiator discretely or continuously throughout the reaction. P reparation of Polymeric Stabilizers

The preferred polymeric stabilizer and the preparation thereof is described in Ref. 7 which is incorporated herein by reference even as Ref. 13. The preferred stabilizing agent is typically an amphiphilic random copolymer that is made of hydrophobic and hydrophilic monomers. The hydrophobic monomers are typically a mixture of methacrylate esters having the following structure:

O Il CH₂=C-C-OR₁

CH₃

wherein R₁ is typically an alkyl group having from 14 to 20 carbon atoms, and somewhat more typically from 16 to 18 carbon atoms, such as hexadecylmethacrylate (C16) and octadecylmethacrylate (C18).

The hydrophilic monomer is typically an acrylic or methacrylic acid having the following structure:

O Il CH₂=C-C-OH

R₂ wherein R₂ is CH3 or H. The hydrophilic component can be comprised solely of methacrylic acid or acrylic acid, or blends thereof. Copolymers prepared from methacrylic and acrylic acid typically contain from about 5 to 15 mol percent

• methacrylic acid and from about 15 to 5 mol percent acrylic acid. The total sum of the acrylic acid and methacrylic acid components varies between 5 and 20 mol%.

It has been discovered that the stabilizing properties of the stabilizing agent are improved by preparing the amphiphilic copolymer from a mixture of linear alkylmethacrylates with different lengths of the hydrophobic moieties. Typically, the hydrophobic component may comprise a mixture of methacrylate esters wherein the alkyl within the ester moiety has about 14 to 20 carbon atoms. A particularly useful stabilizing agent is comprised of methacrylate esters wherein about 90 to 98 % of the methacrylate esters have alkyl moieties that are from 16 to 18 carbon atoms in length. The methyacrylate esters may be prepared from linear alcohols that are from 14 to 20 carbon atoms in length. Suitable methacrylate ester monomers include, without limitation, hexadecyl methacrylate, octadecyl methacrylate, tetradecyl methacrylate, and eicosyl methacrylate.

It has been discovered that the stabilizing properties of the stabilizing agent are improved when the mixture of methacrylate esters is comprised of ester groups having differing lengths.

Typically, the broader the molecular weight distribution of the copolymer, the better the stabilizing agent can stabilize and emulsify acrylamide based polymers. The same trend is also generally observed when increasing the length of the alkyl groups in the alkylmethacrylate monomers. For example, when a hydrophobic co-monomer, such as lauryl methacrylate only is used, the stabilizing effect decreases with the used dispersant concentrations. The stabilizing agent typically has a number average molecular weight that is from about 500 to 50,000 g/mol with a weight average molecular weight between 50,000 and 100,000 g/mol. Observations have generally shown that high molecular weight copolymers may cause decreased suspension stability. While not wishing to be bound by theory, it is believed that a probable reason for the decreased stability results from particle coalescence due to a bridging flocculation in case of polymer molecular weights higher than 100,000 g/mol. The amount of the hydrophobic component to hydrophilic component can be varied from about 95:5 to 30:70 mol percent. Typically, the ratio of hydrophobic to hydrophilic component is from about 95:5 to 80:20, and somewhat more typically, from about 90:10 to 80:20 mol percent.

The synthesis of the stabilizing agent can be performed in an aliphatic hydrocarbon solvent using conventional oil-soluble initiators. The initiator concentration can vary from about 0.1 to 0.3 mol percent, and is typically from about 0.1 to 0.2 mol percent based on the total molar content of the monomers. Typically, the synthesis is performed for 8 hours at temperatures from about 60 ⁰C to 90 ⁰C. The stabilizing agent is preferably present in the inverse-emulsion or inverse-suspension in an amount that is from about 0.1 to 2.5 weight percent based on the total weight of the emulsion or suspension, and more preferably from about 0.1 to 1.0 weight percent based on the total weight of the inverse- emulsion or inverse- suspension. For inverse-suspensions the amount of stabilizing agent is preferably up to about 1.0 weight percent based on the total weight of the suspension, and more preferably up to about 0.5 weight percent.

The polymeric stabilizing agent (IB 14 of reference 7) is one of the possible polymeric stabilizers which can be employed in inverse-suspension polymerization. IB 14 has a weight average molecular weight of 89 kDa, a weight averaged radius of gyration of 8.7 run and an intrinsic viscosity of 0.25- 0.3 dl/g. IB 14 has been polymerized based on 86 mol% of a mixture of methacrylates having C 16 or C 18 alkyl chain length (with a ratio of C16:C18 of 25:75) and 14 mol% of acrylic acid. 20 parts of the stabilizing agent IB 14 are dissolved in 80 parts of aliphatic hydrocarbon (Isopar M) as a solvent. The solution is charged in a 0.5 L glass rector, equipped with mechanical stirrer, cooling-heating jacket and connected to a nitrogen line. The reaction mixture is purged/degassed continuously for 1 hour with nitrogen, the temperature is increased up to 60° C and the reaction is initiated with addition of 0.0005 parts, of 2,2'-azobis(2,4dimethylvaleronitrile). After 3 hours the temperature is increased up to 90 ⁰C and is kept constant for another 5 hours to complete the polymerization reaction. The obtained copolymers are used in a solution as received.

Inversion The water-in-oil inverse-emulsions of the present invention can be self- inverting or can be inverted with the addition of a wetting agent. These wetting agents can be added to the water-in-oil emulsion or can be added to the water into which the emulsion is introduced. Preferably used wetting agents for inverting water-in-oil emulsions are ethoxylated nonylphenols having a degree of ethoxylation between 5 or 20 or alkoxylated fatty alcohols of 10 to 22 carbons, having a degree of allcoxylation between 5 and 20. To someone skilled in the art, it would be clear that there are a variety of other wetting agents which could be employed.

Branched Poly electrolytes

The amount of chain-branching agent in the polymerization process of the invention may be from zero (for linear polyelectrolytes) to between 1 and 1000 ppm for branched polyelectrolytes, preferably between 4 and 100 ppm, more preferably between 4 and about 25 ppm and most preferably between 4 and about 25 ppm.

Typically, a chain-branching agent is a water-soluble multifunctional co- monomer having at least two unsaturated groups. Examples of chain-branching agents include, though are not limited to methylene-bis-acrylamide, divinyl benzene, diethylene glycol diacrylate, propolyene glycol dimethacrylate, dially acrylate, dially fumarate, trimethyloxy propane triacrylate and the like. One or more chain-branching agents may be used.

As was described in references 4-6, the, addition of the chain-branching agent can be controlled using chain-transfer agents. Additionally, the chain- branching agent may be added continually or discretely, as was described in the prior art. The addition of the chain branching agent can begin at the outset of the reaction, or after some fixed time or conversion. The preferred chain-branching agent for this invention was methylene-bis-acrylamide (MBA). To permit a more homogeneous branching distribution, as well as to increase the total amount of branching on the molecule, while retaining polymer solubility, it is desirable not to add all the branching agent at the outset of the polymerization and, therefore, to add it continuously, or semi-continuously during the reaction. As the branching agents are water soluble co-monomers, it is surprising that they can be dosed, either discretely or continuously, to an inverse-emulsion with a continuous organic phase. However, it appears that, provided the multifunctional co-monomer is dissolved in a relatively small amount of water, compared to the total volume of the organic, continuous, phase, the multifunctional co-monomer will dissolve in the oil. This effect is mediated by the presence of surfactants, which enhance the solubility of acrylic water soluble monomers in oil. Some previous academic work has added, semi-continuously, the multifunctional monomer in the form of an inverse-emulsion. However, this risks secondary nucleation, and the non-uniform distribution of multifunctional co-monomer (i.e. the branching agent) in existing droplets. This results in non- homogeneous branching, lower solubility of the resulting polymers, and a lower threshold for branching agent should one wish to keep the polymer soluble, which is generally the case.

The addition of chain branching agent can increase the molar mass, and hence intrinsic viscosity, by increasing the average chain length of given macromolecules. Typically, branched structures are denser, providing, in the case of polyelectrolytes, higher local charge densities. Therefore increasing the charge density of the polymer coil in solution cannot only be done by using monomers having a higher charge (as is the case for the DIPOLEs) but in accordance with the present invention long-chain branching can moreover, be added. Both provide a higher concentration of charges inside the coil radius, the former by increasing the number of charges and the latter by reducing the coil size, for a given molar mass.

Powders, in particular Branched Powders

A powdered polyelectrolyte can be prepared by bulk based solution-gel processes, or via inverse- suspension polymerization. In the case of the latter, the organic phase in the inherently unstable inverse- suspension can separate off to a top layer which can be, either in full or part, decanted. Post processing, after the oil removal, would include the drying of the product. The latter can be based on chemical methods, which could involve extraction with a solvent, a thermal process such as heating, or physical methods, such as centrifugation, or combinations thereof. Examples Preparation of High-Purity Diquaternary Di-ammonium Monomers

The preparation of high-purity diquaternary di-ammonium monomers according to a previous disclosure (Ref.2, which is incorporated herein by reference) is exemplified by the preparation of Dipole-M. It is obtained via the quaternisation of DMAPMA with methylchloride. The quaternization reaction is performed in a 2 litre, jacketed glass autoclave (Biichi AG), equipped with a stirrer, plunger, temperature and pressure probe and equipped with a bottom valve.

To 193 g (0.9 moles) BDMAPMA in 800 g acetonitrile, 115 g (2.27 moles) methyl chloride are added over a period of one hour. The mixture is heated up to 82 ⁰C, the pressure rises to 2 bar. A white solid starts to precipitate. After 23 hours at 80-82⁰C the mixture is cooled to room temperature, the excess of methyl chloride is stripped with nitrogen and the solid monomer product is filtered over a pressure filter. The filtrate is reused in the following reaction. After drying with air and 4 hours under reduced pressure (10 kPa), 285 g solid monomer product containing the DIPOLE-M (BDMAPMA.2MeCl) are obtained. The crystalline powder obtained is used as such for the polymerisation reactions.

The thus prepared monomer product used in the examples has the following composition: 99.5% DlPOLE-M, 0.1% monoquat (BDMAPMA.1CH3CL) and 0.4 % other impurities.

The DIPOLE-A used in the examples was prepared by quaternisation of BDMAPA with methyl chloride in the same manner as described above. It was in the form of a solid monomer product having the following composition : Dipole-A (BDMAPMA.2MeCl) 99.0-99.5%.

Example 1: Preparation of Copolymers of Dipole-M and Dipole-A with acrylamide

Copolymers of high purity, crystalline, diquaternary cationic monomers, specifically DIPOLE-M or DIPOLE-A were prepared via inverse-emulsion using acrylamide (50% aqueous solution) as a non-ionic co-monomer.

Table Ia summarizes the conditions for charged polymers at solid levels between 25 and 30% total solids, with a charge as high as 3.93 mEq (also expressed as a charge density of 124%), prepared with DIPOLE-M.

Table Ib summarizes the conditions for charged polymers at solid levels between 25 and 30% total solids, with a charge as high as 4.11 mEq (also expressed as a charge density of 124%), prepared with DIPOLE-A. Table Ic summarizes the conditions for charged polymers at 37-40% solids with a charge as high as 6.31 mEq (also expressed as a charge density of 200%), prepared with DIPOLE-M. Table Ic is used as an illustration, not only to describe the preparation of highly charged polycations (PolarFloc-M B/Q 1++ and Q/Q 1++) but also to demonstrate that the formulation, at 40% solids and an HLB of 8.0 can function over a full range of cationic monomer levels. Table Ic also illustrates, via example PolarFloc-M H/G 1+, that it is possible to prepare cationic polymers essentially without the addition of extra water (Ig in 4000 g). That is, apart from the water present in the monomer formulations, in this case a 50% aqueous acrylamide solution. Tables Ia, b and c summarize the preferred embodiments of the recipe, though other recipes, specifically compositions, would be evident to someone skilled in the art. Table Ia. Recipe for Inverse-Emulsion Copolymerization of High Purity, Crystalline, Diquaternary Di-ammonium Monomer (DIPOLE-M) with

Acrylamide, resulting in 25-30% solids levels (*♦)

* pH of the aqueous phase adjusted to 3.50. ** Aqueous and Organic phases pre-homogenized for 90 seconds at 8400 RPM in a Silverson

Homogcnizcr.

*** Added discretely in 10 additions, spaced over the time of the reaction, dissolved in Xylene. **** Scavenger added after 6 hours and 90% conversion, dissolved in water.

♦ Rolfor TR/8/L wetting agent. ♦ * All batches were prepared with an average HLB of 5.86. Table Ib. Recipe for Inverse-Emulsion Copolymerization of High Purity, Crystalline, Diquaternary Di-ammonium Monomer (DlPOLE-A) with

Acrylamide, resulting in 25-30% solids levels (♦*)

Homogenizer.

* RolforTR/8/L wetting agent. ♦ ♦ All batches were prepared with an average HLB of 5.88. Table Ic. Recipe for Inverse-Emulsion Copolymerization of High Purity,

Crystalline, Diquaternary Di-Ammonium Monomers with Acrylamide, resulting in 37-40% solids levels (♦»^*>

Homogenizcr.

♦ Rolfor TR/8/L wetting agent. ♦♦ All batches had an average HLB of 7.99. The aqueous and organic phases were prepared separately, than degassed with 99.999% nitrogen for fifteen minutes. Following homogenization, as mentioned in Table 1, for 90 seconds at 8400 RPM, the inverse-emulsion was loaded into a 5L 316-stainless steel reactor with a temperature maintained at 40 ⁰C. Following degassing with 99.999% nitrogen for thirty minutes, to remove oxygen impurities, the first shot of 0.50 g of V65 initiator (in 1.5 g of Xylene) was added. Subsequent additions occurred after 3.0, 4.0, 4.5, 5.0, 5.25 and 5.5 hours, all 0.2 g in 0.6 g of Xylene. Four shots of V65 were added after 90% conversion, between 5.75 and 6.0 hours, each shot comprising 0.2 g of V65 in 0.6 g of Xylene. After six hours NaMBS scavenger was added, in totality, dissolved in 8.4 g of soft water. After cooling the reactor to 32 ⁰C over 20 minutes, the Rolfor wetting agent was added and the reactor drained to sampling reservoirs. For the structured polymer, PolarFloc-M F/A 1 ++, the MBA was added continuously using a dosing pump during the first three hours of the reaction.

For all reactions the temperature was 40 ⁰C for the first hour, with the temperature increased to 45 ⁰C between 60 and 115 minutes following the onset of the polymerization. Typically the systems yielded a white-opaque emulsion with bulk viscosities on the order of 120-300 cP, which is much less than the equivalent emulsions based on copolymers of acrylamide with monoquatemary ammonium monomers, which are on the order of 800-1200 cP. This provides a handling advantage during application to the PolarFlocs of the present invention.

The polymers based on ,said monomers, characterized by physical chemical means, are summarized in Table 2. In all cases, the highly concentrated, crystalline powder form of the diquaternary monomers, which contained only 0.5 % impurities including monoquatemary monomers, was used. It is also possible to use an aqueous solution of the diquaternary monomer, provided the stabilizing agent (e.g. MEHQ) is removed prior to use in the polymerization reaction. The charge densities obtained for the polymer preparations listed in Tables 1 a, b and c are listed in Table 2. PolarFloc-M G/E 1+ yielded an intrinsic viscosity, in 0.05 M NaCl, of 8.06 dl/g. PolarFloc-M E/Q 1 ++ had an intrinsic viscosity, in 0.05 M NaCl, of 10.58 dl/g.

Table 2. Physical Chemical Properties of Polymers Constituting the Embodiment of the Present Invention*

* Polymers prepared at solid levels between 25 and 30 % solid levels had charges as high as 3.93 mEq (also expressed as an upper limit in charge density of 124 %). Polymers prepared at solid levels of 40 % had charges as high as 6.31 mEq (also expressed as an upper limit in charge density of 200%). ** PolarFloc-M refers to polymer prepared with DIPOLE-M as a diqυaternary di-ammonium monomer, whereas PolarFloc-A refers to polymer prepared with

DIPOLE-A as the diquaternary di-ammonium monomer.

***Concentration (ppm) of the difunctional monomer methylenebisacrylamide, relative to the total monomer concentration.

**** weight percent of monomers based on the total emulsion weight.

Example 2

The embodiment of Example 1, wherein an inverse-emulsion can be polymerized with a diquaternary monomer in the absence of excess water. This is described, in Tables Ic and 2 respectively, under the heading PolarFloc-M

H/G 1+.

Example 3

The embodiment of Example 1 wherein an inverse-emulsion can be polymerized with a diquaternary monomer at 40% total solids levels. This is described, in Tables Ic and 2 respectively, under the heading PolarFloc-M G/E

1+, PolarFloc-M E/Q 1++, PolarFloc-M B/Q 1++ and PolarFloc-M Q/Q 1++.

Example 4

The embodiment of Example 1 wherein a highly charged cationic polymer can be prepared with a chain-branching agent added semi-continuously. Specifically, methylenebisacrylamide, at the levels given in Tables Ia to Ic, was added in 20 discreet shots beginning one hour after the polymerization outset, and occurring every fifteen minutes. This is described, in Tables Ia to Ic respectively, under the heading PolarFloc-M H/G. 1+, PolarFloc-M G/E 1+

PolarFloc-M E/Q 1++, PolarFloc-M B/Q 1++, PolarFloc-M Q/Q 1++ , PolarFloc-A G/E1+ and PolarFloc-A F/A1++.

Example 5

The embodiment of Example 1 wherein a branched polyelectrolyte based on a diquaternary di-ammonium monomer can be prepared over a range of charge densities, molar masses (as indicated by Intrinsic Viscosity) and concentrations (total solids level). This is described, in Tables Ia, Ic and 2 respectively, under the heading PolarFloc F/ A 1++, for Table Ia, and PolarFloc- M H/G 1+, PolarFloc-M G/E 1+, PolarFloc-M E/Q 1++, PolarFloc-M B/Q 1++ and PolarFloc-M Q/Q 1++ for Table Ic. Example 6 In one embodiment, the use of polymeric surfactants was also shown to produce large microbeads (ca 100 micrometers versus 0.1 to 0.2 micrometers, on average, for inverse-emulsions based on fatty acid esters) which could be suitable if the high charged polymer was required in powdered form, since the larger beads can be easily settled, filtered and dried. Example 6 presents a synthesis of cationic acrylamide based polymer containing 25 molar percent of DIPOLE-M, with the remaining monomer balance being acrylamide. The overall batch size was 50Og.

The aqueous phase was prepared by dissolving 31.25 grams of DIPOLE- M in 187.50 grams of a 50% acrylamide solution in water. Subsequently, 31.20 grams of demineralized water was added, followed by 0.027 grams of EDTA and 0.027 grams of octadecyltrimethylammonium chloride. The pH was then adjusted to 3.5 by addition of lactic acid.

The organic phase was prepared by dilution of 3.0 grams of a polymeric stabilizing agent (IB 14 of Reference 7), as a 20 wt% solution in ISOPAR-M, and 1.4 grams of sorbitan sesquioleate in 245.6 grams of Exoll DlOO.

The polymeric stabilizing agent (IB 14 of reference 7) has a weight average molecular weight of 89 kDa, a weight averaged radius of gyration of 8.7 nm and an intrinsic viscosity of 0.25-0.3 dl/g. The polymeric dispersant contains 86 mol% of a mixture of methacrylates having C16 or Cl 8 alkyl chain length (with a ratio of Ci₆:Ci₈ of 25:75) and 14 mol% of acrylic acid.

The preparation of the inverse-suspension is as follows. After degassing, the polymerization is initiated by addition of 0.023 grams of 70 percent water solution of t-buty Hydroperoxide and followed by continuous addition of 0.018 grams of sodium methabisulfite in 5 grams of demineralized water for 25 minutes at 35° C. Concomitant with the addition of the t-butylhydroperoxide, a solution of 0.003 g of methylenebisacrylamide is added continuously, using a syringe pump, dissolved in 4.375 grams of demineralized water. After 3 hours the temperature is increased up to 55° C for another hour.

The final suspension is substantially free from any agglomeration and is separated by decanting off the organic phase, which separates away as a supernatant within fifteen minutes, filtering, washing with acetone and isopropanol, sequentially, then drying under vacuum. The final product is a water-soluble branched powder, made by inverse-suspension polymerization, with a diquaternary di-ammonium monomer. To the inventors' knowledge this is the first demonstration of such. Example 7

The polyelectrolytes have been found to have high charge densities, even at low diquaternary monomer levels, and function well in solid-liquid separations, showing advantages to water clarification relative to polyelectrolytes based on co- or ter-polymers of acrylamide and mono- quaternary ammonium monomers, such as dimethyl aminoethyl acrylate-methyl chloride and dimethylaminoethyl methacrylate-methyl chloride.

Flocculation with highly charged polyelectrolytes based on diquaternary di-ammonium monomers has been carried out to demonstrate that each diquaternary di-ammonium group can replace two mono-quaternary ammonium groups. Table 3 summarizes the results of nine tests on a variety of water and sludge types. This demonstrates that, indeed, half the amount of charged monomers (exactly 49.5%) is required in a diquatemary-based polymer relative to monoquaternary-based polymers. In other words, two polymers, with the same charge density, one prepared from diquaternary di-ammonium monomers and the second from mono-quaternary ammonium monomers can function as substitutes. Furthermore, the dosage of diquaternary-based polymers was, on average, equivalent or slightly below that for the monoquaternary-based polymers (15.1 ppm for the PolarFloc, based on diquaternary monomers, versus 16.0 ppm for the AlpineFloc™ based on monoquaternary ammonium monomers). Table 3. Summary of PolarFloc Testing on a Variety of Water Types"

*PolarFlocs basedon between 10 to 75 wt% diquaternary di-ammonium monomer were evaluated over a range of dosages with the optimum reported. In all cases, a range of AlpineFlocs, based on 10-90 wt% monoquaternary ammonium monomers were also tested, over the same concentration range. In both cases, the result providing the lowest dosage and suitable dewatering kinetics is reported. Example 8

Flocculation with highly charged, linear, polyelectrolytes based on a crystalline powder form of diquaternary di-ammonium monomers have been evaluated in regards to the final dry material content of the sludge. Table 4 provides an example with a biological sludge revealing that the linear PolarFlocs described in this invention, specifically that based on the DlPOLE-A diquaternary monomer, can provide a higher amount of dry material than the corresponding AlpineFloc™ (ref 4-6) based on monoquaternary ammonium monomers.

Table 4. Comparative Results from a Municipal WWTP (Geneva) evaluating flocculants based on monoquaternary ammonium monomers

(AlpineFloc^{1 M}) and diquaternary di-ammonium monomers (PolarFloc) with respect to dry material levels of the separated sludge.

* Inflow of water containing both municipal and industrial effluent, principally.

Example 9

Flocculation with highly charged, branched, polyelectrolytes based on crystalline powder forms of diquaternary di-ammonium monomers, has been evaluated in regards to dewatering kinetics. Table 5 illustrates, for a structured PolarFloc, based on the diquaternary di-ammonium monomer DlPOLE-M, a more rapid dewatering and more extensive dewatering.

Table 5. Comparative Results from a Municipal WWTP evaluating branched flocculants based on monoquaternary di-ammonium monomers (AlpineFloc™) and branched diquaternary di-ammonium monomers (PolarFloc) with respect to dewatering kinetics.

*AlpineFloc™ El+ has 50 wt% cationic monomer (trimethylaminoethyl acrylate) whereas PolarFloc G/E 1+ has 25 wt% of diquaternary monomer

(DIPOLE-M). Both have the same charge density, as defined earlier in the patent, and each has approximately one long-chain-branch per polymeric chain.

Example 10

Flocculation tests with polyelectrolytes based on crystalline powder forms of diquaternary di-ammonium monomers have been performed on several occasions. Table 6 provides an example with a biological sludge revealing that the PolarFlocs described in this invention can function at a lower dosage than the corresponding AlpineFloc™ (ref 4-6) based on monoquaternary ammonium monomers.

Table 6. Comparative Results from a Municipal WWTP comparing flocculants based on monoquaternary ammoniums

(AlpineFloc™) and diquaternary di-ammonium monomers (PolarFloc).

* Biological sludge from a strictly municipal inflow with an inlet concentration of 2g/L.

REFERENCES

1. D. Hunkeler, F. Candau, C. Pichot, J. Guillet, T. Y. Xie, A.E. Hamielec, J. Barton V. Vaskova, M. Dimonie, K.H. Reichert, "A Chemical, Physical and

Colloidal Comparison of Heterophase Polymerizations: A New Systematic Nomenclature", Advances in Polymer Science, 112 (1994).

2. I. Vanden Eynde, P. Vanneste, S. Eeckhaoudt, R. Loenders, International Patent Application PCT/EP2004/052056 (filed September 6, 2004); I. Vanden Eynde, P. Vanneste, S. Eeckhaoudt, R. Loenders, European Patent Application, No. 1 512 676 published on March 9, 2005. 3. D. Tembou N'Zudie, Y. Legrand, US Patent Application US 2002/0035198

Al, March 21, 2002. 4. J. Hernandez Barajas, C. Wandrey, D. Hunkeler, US Patent 6,294,622 Bl (September 21, 2001).

5. J. Hernandez Barajas, C. Wandrey, D. Hunkeler, US Patent 6,617,402 (September 9, 2003).

6. J. Hernandez Barajas, C. Wandrey, D. Hunkeler, US Patent 6,667,374 (December 23, 2003).

7. I. Pantchev, D. Hunkeler, US Patent Application No. 10/991,628, Polymeric Stabilizing Agent for Water-in-Oil Polymerization Processes. Filed November 18, 2004.

8. A. Riondel, D. Tembou N'Zudie, M. Esch, V. Chaplinski, D. Vanhoye, US 6,673,884 B2 (Published January 6, 2004).

9. C. Vladimier, D. Tembou N'Zudie, A. Riondel, WO 01/55088 A2 (Published August 2, 2001)

10. A. Riondel, EP 1253137 Al (Published October 30, 2002).

11. J.-L. Zeh, L. Sabatier, S. Lepizzera, US 2002/0103331 Al (Published August 1, 2002).

12. S. Fischer, D. Bardoliwalla, R. Grinstein, G. Speenburgh, US 4,751,322 (Published June 14, 1988).

13. 1. Pantchev, D. J. Hunkeler "Influence of quaternary ammonium salt addition on the surface activity of polyacrylic dispersants" Journal of Applied Polymer Science Volume 92, Issue 6, Date: 15 June 2004, Pages: 3736-3743

Claims

1. A polyelectrolyte prepared from a monomer composition comprising, per 100 parts by moles of monomers:

1) from 15 to 100 parts by moles of at least one (meth)acryl di-ammonium salt of formula (1)

(I) wherein R¹ represents hydrogen or methyl, each R², independently, represents an alkyl comprising from 1 to 4 carbon atoms, each R³, independently, represents an alkyl or an aralkyl and each X^", independently, represents an anion; and * 2) from 0 to 85 parts by moles of one or more other charged,or uncharged co- monomers, including optionally at least one chain branching agent, the polyelectrolyte being either linear and has an intrinsic viscosity, measured at 20°C in 0.05 M NaCl, higher than 8 dl/g and a charge density higher than 90% or the monomer composition comprises at least one branching agent so that the polyelectrolyte is branched, the branched polyelectrolyte having preferably an ' intrinsic viscosity, measured at 2O⁰C in 0.05 M NaCl, higher than 7 dl/g, preferably higher than 8 dl/g, and a charge density higher than 30%, preferably higher than 50% and more preferably higher than 90%.

2. A polyelectrolyte according to claim 1, characterised in that the monomer composition from which it is prepared comprises, per 100 parts by moles, more than 20 parts by moles, preferably more than 35 parts by moles and more preferably more than 50 parts by moles of said at least one (meth)acryl di- ammonium salt of formula (I).

3. A polyelectrolyte according to claim 1 or 2, characterised in that the monomer composition from which it is prepared comprises, per 100 parts by moles, less than 99 parts by moles, preferably less than 95 parts by moles and more preferably less than 90 parts by moles of said at least one (meth)acryl di-ammonium salt of formula (1).

4. A polyelectrolyte according to any one of the previous claims, characterised in that it has an intrinsic viscosity higher than 10 dl/g, preferably higher than 15 dl/g and more preferably higher than 20 dl/g.

5. A polyelectrolyte according to any one of the previous claims, characterised in that it is obtained from a monomer composition containing at least one chain-branching agent selected from the group consisting of methylene- bis-acrylamide, divinyl benzene, diethylene glycol diacrylate, propylene glycol dimethacrylate, diallyl acrylate, diallyl fumarate, trimethyloxy propane triacrylate, the monomer composition preferably comprising methylene-bis- acrylamide.

6. A polyelectrolyte according to any one of the claims 1 to 5, characterised in that the monomer composition comprises the chain-branching agent in an amount, based on the total amount of monomers and co-monomers, of between 1 and 1000 ppm, preferably between 4 and 100 ppm, and more preferably between 4 and 25 ppm.

7. A polyelectrolyte according to any one of the previous claims, characterised in that it is prepared by a heterophase water-in-oil process from the monomer composition.

8. A polyelectrolyte according to any one of the claims 1 to 7, characterised in that it is in the form of a powder.

9. A polyelectrolyte according to any one of the claims 1 to 7, characterised in that it is in the form of an inverse-dispersion, in particular in the form of an inverse-emulsion or an inverse- suspension.

10. A polyelectrolyte according to claim 9, characterised in that the inverse- dispersion has a polymeric solid content higher than 25 weight percent, preferably higher than 35 weight percent and more preferably higher than 40 weight percent.

11. A polyelectrolyte according to claim 9 or 10, characterised in that the inverse-dispersion comprises one or more surfactants, the surfactant or the blend of surfactants when more than one surfactant is present having an HLB between 2 and 10, preferably a HLB higher than 6 and more preferably higher than 7, said one or more surfactants being present in an amount between 0.1 to 5 weight percent based on the total weight of the inverse-dispersion, for an inverse-suspension preferably in an amount between 0.1 and 1 weight percent and for an inverse-emulsion preferably in an amount between 2 and 4 weight percent.

12. A polyelectrolyte according to any one of the claims 1 to 11, characterised in that in formula (I) R² is methyl.

13. A polyelectrolyte according to any one of the claims 1 to 12, characterised in that in formula (1) R³ is methyl or benzyl, preferably methyl.

14. A polyelectrolyte according to any one of the claims 1 to 13, characterised in that in formula (I) R¹ is methyl.

15. A polyelectrolyte according to any one of the claims 1 to 14, characterised in that the monomer composition comprises between 1 and 85 parts by moles of at least one water-soluble co-monomer of formula (II)

CHz^R'-CO-NR^³ wherein R¹ represents hydrogen or methyl and R² and R³ , which may be identical or different,, each independently represent hydrogen or an alkyl comprising 1 to 5 carbon atoms, optionally comprising one or more hydroxyl groups.

16. A polyelectrolyte according to any one of the claims 1 to 15, characterised in that the monomer composition comprises between 1 and 85 parts by moles of at least one water-soluble co-monomer selected from the group consisting of acrylamide, methacrylamide, N-methylolacrylamide, N- vinylmethylacetamide, N-vinylrnethylformamide, dialkylaminoalkyl- (meth)acrylamide, sulphomethylated acrylamide, vinyl acetate, N- vinylpyrrolidone, methyl(meth)acrylate, styrene, dialkylaminoalkyl- (meth)acrylate, 1.3-bis(dimethylamino)-2-propyl (meth)acrylate, 1,3- bis(trimethylammonium)-2-propyl (meth) acrylate chloride, trimethylaminoethyl (meth) acrylate-methyl, diallyldimethylammonium chloride, (meth)acryl- amidopropyltrimethylammonium chloride, (meth)acrylic acid, sodium (meth)acrylate, itaconic acid, sodium itaconate, 2-acrylamide 2-methyl propane sulphonate, sulphopropyl(meth)acrylate.

17. A polyelectrolyte according to any one of the claims 1 to 16, characterised in that it has a charge density higher than 95%, preferably higher than 100%, more preferably higher than 110% and most preferably higher than 120%.

18. A process for manufacturing a polyelectrolyte according to any one of the claims 1 to 17 which is either linear and has an intrinsic viscosity, measured at 20⁰C in 0.05 M NaCl, higher than 8 dl/g and a charge density higher than 90% or which is branched and has preferably an intrinsic viscosity, measured at 2O⁰C in 0.05 M NaCl, higher than 7 dl/g, preferably higher than 8 dl/g, and a charge density higher than 30%, preferably higher than 50% and more preferably higher than 90%, which process comprises the steps of: a) preparing a polymerisation reaction mixture comprising a monomer composition which comprises, per 100 parts by moles of monomers:

(I) wherein R¹ represents hydrogen or methyl, each R², independently, represents an alkyl comprising from 1 to 4 carbon atoms, each R³, independently, represents an alkyl or an aralkyl and each X^", independently, represents an anion; and 2) from 0 to 85 parts by moles of one or more other charged or uncharged co- monomers, including optionally at least one chain branching agent; and b) polymerising the reaction mixture to achieve the polyelectrolyte.

19. A process according to claim 18, characterised in that the polymerisation reaction mixture is prepared by: al) forming an aqueous phase containing the monomer composition; a2) forming an organic phase; and a3) emulsifying the aqueous phase in the organic phase using at least one surfactant to form an inverse-dispersion.

20. A process according to claim 19, characterised in that said surfactant, or the blend of said surfactants when more than one surfactant is used, has an HLB higher than 6 and preferably higher than 7, the HLB of said at least one surfactant being preferably lower than 10, more preferably lower than 9.

21. A process according to claim 19 or 20, characterised in that for forming said aqueous phase use is made of a monomer product containing said at least one (meth)acryl di-ammonium salt of formula (1), which monomer product contains, per kilogram of said salt, less than 20 g, preferably less than 5 g, and more preferably less than 2 g of impurities which may stop the chain growth reducing the average chain length during the polymerisation reaction.

22. A process according to claim 21, characterised in that said monomer product containing said at least one (meth)acryl di-ammonium salt of formula (I) contains, per mole of this salt, less than 0.1 mole, preferably less than 0.05 mole and more preferably less than 0.01 mole, of the corresponding amino- (meth)acrylate ammonium salt of formula (III)

( Il

23. A process according to claim 21 or 22, characterised in that said monomer product containing said at least one (meth)acryl di-ammonium salt of formula (I) and used for forming said aqueous phase is prepared by (1) the reaction of the di-amino (meth)acrylate of formula (IV)

with at least one alkyl or aralkyl derivative of formula R³X in an organic solvent containing at most 5000 ppm, preferably at most 1000 ppm, of water and wherein the compound of formula (I) has a solubility at 25 ⁰C of less than ] g/100 g of solvent, preferably of less than 0.5 g/100 g of solvent, and wherein the solubility of the corresponding amino-(meth)acrylate ammonium salt of formula (III) has a solubility at 25 ⁰C of at least 20 g/100 g of solvent ; and (2) the separation of the monomer product containing the compound of formula (I) from the reaction mixture without dissolving it in water, the compound of formula (I) being separated from the reaction mixture in the form of a solid product comprising, per mole of the compound of formula (I), less than 0.1 mole, preferably less than 0.05 mole and more preferably less than 0.01 mole of the compound of formula (III).

24. A process according to any one of the claims 21 to 23, characterised in that said monomer product which is used for forming said aqueous phase is a solid product, which solid product is preferably dissolved in said aqueous phase which contains already a dissolved co-monomer.

25. A process according to any one of the claims 19 to 24, characterised in that said aqueous phase is prepared such as to contain a minimum of water or an amount of water which is at the most 10% higher, preferably at the most 5% higher, than the minimum amount of water required to dissolve the monomer composition.

26. A process according to any one of the claims 19 to 25, characterised in that the aqueous phase is emulsified in the organic phase to form an inverse-emulsion, using in particular an amount of between 1.5 and 5 weight percent of said at least one surfactant, based on the total weight of the inverse- emulsion.

27. A process according to any one of the claims 19 to 25, characterised in that the aqueous phase is emulsified in the organic phase to form an inverse-suspension, using in particular an amount of between 0.1 and 1.5 weight percent of said at least one surfactant, based on the total weight of the inverse-emulsion.

28. A process according to claim 27, characterised in that it comprises the further steps of: c) removing the organic phase after having polymerised the reaction mixture; and d) drying the obtained polymeric product.

29. A process according to claim 27 or 28, characterised in that a stabilizing agent is added to the reaction mixture.

30. A process according to claim 29, characterised in that the stabilizing agent comprises at least one stabilizing polymer derived from a hydrophobic mixture of methacrylate monomers having the following formula

(A):

O Il

(A) CH₂=C-C-OR₁

I CH₃ wherein Ri is an alkyl group from 14 to 20 carbon atoms; and a hydrophilic monomer component having the following formula (B) O

(B) ^r CH₂=C-C-OH ^i;

R₂ wherein R₂ is CH₃ or H, and wherein the stabilizing agent has a number average molecular weight that is from about 500 to 50,000 g/mol, the stabilizing polymer being preferably derived from said hydrophobic mixture wherein the methacrylate monomers are about 90 to 98 % methacrylates having alkyl groups that are 16 to 18 carbon atoms in length and wherein component (B) is comprised of a mixture of acrylic acid and methacrylic acid.

31. A process according to any one of the claims 18 to 30, characterised in that during the polymerisation of the reaction mixture at least one chain-branching agent is added thereto, in particular in a continuous or semi- continuous way.

32. A process according to claim 31 , characterised in that, based on the total amount of monomers and co-monomers, the chain-branching agent is added to the reaction mixture in an amount of between 1 and 1000 ppm, preferably between 4 and 100 ppm, and more preferably between 4 and 25 ppm.

33. A process according to claim 31 or 32, characterised in that said at least one chain-branching agent is selected from the group consisting of methylene-bis-acrylamide, divinyl benzene, diethylene glycol diacrylate, propylene glycol dimethacrylate, diallyl acrylate, diallyl fumarate, trimethyloxy propane triacrylate, the chain-branching agent preferably comprising methylene- bis-acrylamide.

34. A method of increasing the rate of water removal during the dewatering of wet sludges derived from municipal or industrial effluents which comprises adding to the wet sludges at least one polyelectrolyte as claimed in any one of the claims 1 to 17 in an amount sufficient to increase the rate of water removal.

35. A method of increasing the dry material levels during the dewatering of wet sludges derived from municipal or industrial effluents which comprises adding to the wet sludges at least one polyelectrolyte as claimed in any one of the claims 1 to 17 in an amount sufficient to increase the dry material content of the resulting sludge.

36. A method of improving the filtrate clarity during the dewatering of wet sludges derived from municipal or industrial effluents which comprises adding to the wet sludges at least one polyelectrolyte as claimed in any one of the claims 1 to 17 in an amount sufficient to improve the filtrate clarity.

37. A method of increasing the decantation rate of industrial waters which comprises adding, prior to or in the decanter, at least one polyelectrolyte as claimed in any one of the claims 1 to 17 in an amount sufficient to improve the clarity of the supernatant at the exit of the decanter.

38. A method of flocculating solids from an aqueous composition containing suspended or dissolved solids which comprises adding to said aqueous composition a flocculant comprising at least one polyelectrolyte as claimed in any one of the claims 1 to 17 in an amount sufficient to cause flocculation of said solids.