THIS INVENTION relates to a method of producing polymerised homopolymers of acrylamidosulphonic acid or like substances or their ammonium or metallic salts and copolymers of the said acid or its derivatives with other water soluble monomers such as vinyl monomers. It is an object of the invention to provide an improved method of manufacturing such polymers or copolymers.

According to this invention there is provided a method of producing a polymer of acrylamidoalkylsulphonic acid, said method comprising steps of creating a solution of acrylamidoalkyl-sulphonic acid monomer or salt in solvent, adding to the solution a photosensitizer to initiate photopolymerisation and subsequently exposing the solution to light to initiate a polymerisation reaction, reducing the solvent content of the material and reducing the material to an appropriate particle size. Preferably the solvent is water.

Advantageously a monomer stabiliser or free radical inhibiter is added to the solution and advantageously a chain transfer agent is added to the solution. Preferably a sequestering agent is added to the solution.

The liquid solution may be fed into trays which are fed on a moving conveyor belt beneath a band of ultraviolet light tubes to initiate the polymerisation reaction.

The acryla ido sulphonic acid monomers or their salts relevant to the present invention can generally be represented

H-c ^" R.

CH

I

0=0

where R _: is a hydrogen atom or an alkyl group having from 1 to 10 carbon atoms. More specifically R, is an aliphatic group having 1 to about 3 carbon atoms. R _2/ R ₃ , R ₆ , and R ₅ , independently can be hydrogen atoms or alkyl groups with the proviso that the total number of carbon atoms in each alkyl group is 8 or less. Preferably R ₂ and R ₃ are methyl groups. Desirably R ₄ and R-, independently, are hydrogen atoms or alkyl groups having from 1 to 8 carbon atoms, with hydrogen being preferred. M is a hydrogen ion, an ammonium ion, a metal cation or mixtures thereof. The metal cation can generally be any zinc, sodium, potassium or the like. Sodium and potassium are especially preferred. Typically, the monomers are utilised in the form of their salts. A highly desirable monomer for making either a homopolymer or a copolymer is 2-acrylamido-2-methylpropanesulphonic acid sodium salt hereinafter referred to as AMPS.

The storage of acrylamidoalkylsulphonic acid or salt containing monomers as well as polymerisation thereof generally occurs in the presence of a solvent. Water, is the preferred solvent for the preparation of both homopolymers and copolymers of the acrylamidoalkylsulphonic acid or salt containing monomers because of the limited

solubility of the monomers in most organic solvents. Other suitable but less desirable solvents include dimethylformamide, dimethylsulphoxide, methanol, ethanol and other polar solvents. The amount of the acrylamidoalkylsulphonic acid or salt containing monomer, or combinations of the various such different monomers in the solvent generally ranges from about 10% to about 100% by weight based upon the weight of the monomer and solvent. Generally, an amount is utilised which is less than the saturated weight amount of the monomer in the solvent. With regard to an aqueous solution, the amount of monomer is generally from about 40 to 70% by weight, desirably from about 40% to about the saturation point of the aqueous solution, preferably from about 50% to about the saturation point of the aqueous solution, more preferably from about 50% to about 60% and highly preferably from about 55% to about 60% by weight based upon the weight of said monomer and said aqueous solution. Such high amounts by weight of the monomer are desirable in that the polymerisation thereof results in higher yields, higher molecular weight, better performance properties and ease of handling.

A wide variety of co polymers can be prepared utilising suitable comonomers. Generally, the comonomer is such that the overall co polymer is soluble in the solvent and preferably soluble in water. Most often the comonomer itself is water soluble. The various comonomers will contain a vinyl group and generally a nitrogen and/or oxygen atom. Thus, various actylamides, various vinyl pyrrolidones, various vinyl caprolactams, various actylates, various acrylonitriles, various maleic acids and maleic anhydrides, various styrene sulphonic acids and salts thereof, as well as various acrylic acids can be utilised. By the term "various" it is meant the different compounds, derivatives or salts thereof known to the art

and to the literature. Considering the acrylamides, specific examples of monomers include methacrylamide, N, N- dimethylacrylamide, diacetone-acrylamide, dimethylaminopropylmethacrylamide, t-butylacrylamide, acrylamide, and the like. Examples of suitable pyrrolidones include N-vinylpyrrolidone and the like. Various caprolactams include N-vinylcaprolactam and the like.

Suitable acrylates include t-butylacrylate, methylacrylate, dihydroicycolopentadienylacrylate , 4 - butanediolmonoacrylate, diethylaminoethylacrylate, methylmethacrylate, and the like. Examples of various acrylonitriles include acrylonitrile, chloroacrylonitrile, methacrylonitrile, and the like. Besides maleic anhydride or acid, various derivatives and salts thereof can be utilised. In addition to acrylic acid, various derivatives thereof can be utilised such as methacrylic acid, and the salts of these acid. Various styrene sulphonic acid include 4-styrene sulphonic and isomeric forms of the said acid and its salts. Preferred comonomers of the present invention include N-vinylpyrrolidone, N, N- dimethylacrylamide, diacetoneacrylamide, acrylamide, N- vinylcaprolactam, and t-butylacrylamide with N, N- dimethylacrylamide being highly preferred.

Desirably, the comonomers have good solubility in the solvent. Should the comonomer not have good solubility, it is then desirable to utilise a small portion of another solvent such as an alcohol, for example methanol, to render the comonomer soluble in the solvent such as water. The amount of comonomer utilised as well as the type of copolymer desired. Generally, it will vary from about 0.1% to about 30% by weight, desirably from about 1% to about 15% and preferably from about 3% to about 8% by weight based upon the total weight of all the monomers.

An important aspect of the present invention is the use of photochemical initiators or photosensitizers which in the presence specific of electromagnetic radiation, e.g. ultraviolet or visible light, induce free radical polymerisation reactions. Photochemical initiators enable free radical reactions, specifically free radical polymerisations of unsaturated compounds, to occur by being able to absorb radiant energy and transfer it to a substrate unsaturated compound. Once a substrate has been so activated to create free radical chain polymerisation can take place until the desired molecular weight of polymer gas been obtained. The reaction can curtailed either intentionally or otherwise to yield a lower molecular weight polymer. The extent of reaction and hence molecular weight of polymer can be controlled by the time irradiation and the concentration of photosensitizer.

Photosensitizers are molecules which absorb specific wavelengths of radiation and form free radicals. Among these molecules are polynuclear aromatic compounds, halogens, halogenacids and carbonyl containing compounds. Various polynuclear aromatic compounds include anthracene, naphthalene phenanthrene and the like. Examples of halogens are fluorine, chlorine, bromine, and iodine and also combinations of the atomic halogens in molecular form e.g. I-Br. Various halogen acids include hydrofluoric acid, hydrochloric acid, hydrobromic acid and hydriodic acid. Examples of carbonyl compounds are those containing the following structure:-

C = 0

R?

wherein R- _. and/or R ₂ can be H, an alkyl-group having 1 to 16 carbon atoms, aromatic, substituted aromatic or combinations of alkyl, aromatic, and substituted esters and ethers.

The radiative energy applied to the system is generally in the wavelength range 200 - 750 nM which is the visible and ultraviolet range of the spectrum. The preferred photosensitizers described herein require UV light of wavelength 250 - 400 nM for free radical generation and hence efficient photopolymerisation of said unsaturated compounds.

In preferred embodiments of the present invention the said monomers or mixtures of monomers are dissolved in the appropriate solvent, preferably water, to the required concentration in a stirred vessel. The pH is controlled to between 3.0 - 10.0. To this may be added various chemicals with specific functions with regard to the process, for example as follows:-

(a) Monomer stabilizer or free radical inhibitor to prevent premature autopolymerisation at the storage stage thus giving uncontrolled reaction and unpredictable product.

(b) Chain transfer agent to control the extent of polymerisation and chain length.

(c) A photosensitizer to initiate photopolymerisation.

(d) A sequestering agent to scavenge metal compound stabilisers.

Chain transfer agents terminate one growing polymer chain and start another, they are not inhibitors as they do not alter the rate of polymerisation but reduce molecular weight. Compounds which are chain transfer agents are

those which donate hydrogen readily and include thiols (e.g. butane thiol and sodium formate) . Other compounds readily form stable free radicals, for example carbon tetrabromide and pentaphenylethane.

Various free radical inhibitors are compounds with active hydrogenations e.g. phenols, aminos and the like. Other compounds are those that stabilize by other complexing mechanisms, particularly known are quinones e.g. benzoquinone, monomethylether of hydroquinone, and tetrachloroquinone and the like. Other inhibitors which are used are inorganic redox materials e.g. ferric chloride and copper sulphate.

The contents of the vessel are stirred for sufficient time to allow for sufficient and even mixing. The liquid mix is then fed into trays which are conveyed on a moving belt beneath a bank of UV light tubes. It is preferable that a sequestering agent be added as the liquid is transferred to the reaction trays, preferably via a static mixer or other similar device. Such sequestering agents are used when metallic inhibitors are used such as Cu ²⁺ or Fe ³⁺ . Various sequestering agents include ethylene diamine tetra-acetic acid, diethylene triamine penta-acetic acid, N-hydroxylethyl ethylene diamine tri-acetic acid, N,N-di-(hydroxy ethyl) glycine, glucoheptonic acid and the like.

The UV light catalyses the reaction and success is indicated by a temperature rise and increase in viscosity of the liquid mix. The trays are from 1cm to 300cm deep, more preferably from 5cm to 15cm deep. The width and length are determined by the rate of production required and the width and depth of the bank of UV tubes used. The time of reaction is from 10 sec. to 30 mins. more

preferably from 1 min. to 20 min. and even more preferably from 2 min. to 6 min. Successful polymerisation is demonstrated by the discharge of the product as a viscous sticky mass.

The final process in producing polymer involves reducing the appropriate 50% water content of the material to between 0 and 20% or more preferably between 8 and 12% by appropriate means such as oven drying, or drying under infrared lights, or a source of microwave energy, on a steel conveyor belt. Alternatively the polymer may be dried by spreading the sticky mass in a thin layer on to the surface of polished steel rollers slowly rotating and maintained at temperatures between 100°C and 200°C by such means as internal hot fluid or steam circulation.

The resultant dry material is present as a combination of fine powder and integrated sheets of polymer flake. The product is conveyed to a chopping grinding and sieving station where the material is reduced to the appropriate particle size.

EXAMPLES

1. POLYMERSISATION OF THE SODIUM SALT OF 2-ACRYLAMIDO- 2-METHYLPROPANE SULPHONIC ACID a. PREPARATION OF THE SODIUM SALT OF SAID MONOMER - Into a 600 L stainless steel mixer tank fitted with an agitator, cooling coils, and outlet valve was added 200 L of mains tap water, 40gm of CusO 5H ₂ 0 (pre-dissolved in 0.5 L warm water) and 226kg of 2-acrylamido-2-methylpropane sulphonic acid (A.M.P.s). The mixture was stirred for one hour until all the monomer had dissolved.

To this was added slowly 100 L of 70° TW sodium hydroxide solution (42% W/V) ensuring that the temperature did not exceed 35°C. The final pH was adjusted to 6.5 with either sodium hydroxide solution or concentrated sulphuric acid, the final temperature to 20°C.

b. PHOTOCHEMICAL POLYMERISATION OF A.M.P.S SODIUM SALT To the monomer solution was added

4 L of 25% aqueous sodium formate solution

5 L of 2% aqueous Irgacure 651 (Ciba Geigy) 2.5 L of 2% aqueous Wako VSO (Berk Chemicals)

Sufficient time was provided for adequate mixing, one hour. The above mixture was then pumped from that tank through a static mixer (Sulzer Bros) into reaction trays of dimensions 550mm (length) , 350mm (width) and 150mm (depth) , conveyed on a belt at 4m/hr. Added to the mainstream prior the static mixer was a 61 solution of ethylene diamine tetra acetic acid (disodium salt) at a rate of 0.8 L/hr., the monomer mix solution being pumped at a controlled rate of 200L/hr.

The monomer mix in the trays was then subjected to ultraviolet light. The bank of UV lamps was 1200mm long, 400mm wide and at a height of 200mm above the surface of the liquid. The time of photosensitization was between 15 and 25 mins. The temperature increase indicative of polymerisation was measured as between 40°C and 60°C.

The gelled mass was transferred from the trays on to a surface coated with polytetrafluoroethylene coated surface. The mass was then cut into small cubes. The small cubes were spread over the surface of a conveyor belt. The conveyor belt was moved beneath a source of microwave energy, and the cubes of polymer were subjected to microwave radiation for approximately twenty minutes to

reduce the solvent content of the monomer. At the end of this drying process the moisture content of the polymer was between 6% and 12%.

The resultant dried mass was milled to a desired particle size, sieved and weighed.

2. POLYMERISATION OF THE SODIUM SALTS OF 2 - ACRYLAMIDO - 2 - METHYL-PROPANE SULPHONIC ACID AND 4 - STYRENE SULPHONIC ACID. a) PREPARATION OF SODIUM SALTS OF MONOMERS

To a 600 L mixer tank described above was added 200 L mains water, 12 g of the monomethylether of hydroquinone (M.M.E.M.q) 133 kg of - 2 - acrylamido - 2 - methylpropane sulphonic acid, and 120 kg 4 - styrene sulphonic acid. The mixture was stirred for one hour to dissolve. To this was added slowly 100 L of 70° TW sodium hydroxide solution ensuring that the temperature did not exceed 35°C. The final pH was adjusted to 6.5 as previously described, the final temperature to 20°C. b) PHOTOCHEMICAL POLYMERISATION OF A.M.P.s. and 4 - STYRENE SULPHONIC ACID SODIUM SALT.

To the mixture of monomers in aqueous solution was added:

1.0 kg of Pentaphenylethane.

3.0 L of 10% Irgacure 907 (Ciba Geigy) .

- Photosensitizer. 0.4 kg acetyl peroxide.

Sufficient time was provided for adequate mixing, one hour.

The above mixture was pumped directly into ■ the reaction trays as described above and conveyed on a belt at 2 m/hr. The aqueous mixture was then subjected to ultraviolet light as described previously. The time of

photosensitization was between 30 and 50 min. , the temperature increase between 30 and 55°C.

The gelled mass was dried, milled, sieved, and weighed as described above.