Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F6/00—Post-polymerisation treatments
  • C08F6/006—Removal of residual monomers by chemical reaction, e.g. scavenging
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/04—Polymerisation in solution
  • C08F2/10—Aqueous solvent
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/46—Polymerisation initiated by wave energy or particle radiation
  • C08F2/48—Polymerisation initiated by wave energy or particle radiation by ultraviolet or visible light
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
  • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F220/10—Esters
  • C08F220/22—Esters containing halogen
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
  • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F220/52—Amides or imides
  • C08F220/54—Amides, e.g. N,N-dimethylacrylamide or N-isopropylacrylamide
  • C08F220/56—Acrylamide; Methacrylamide

Definitions

• the present invention relates to a process for making water soluble or water swellable polymers, by polymerisation of water soluble ethylenically unsaturated monomer or monomer blend.
• the invention relates to processes of making said polymers containing low concentrations of residual monomer.
• Water soluble and water swellable polymers are used in numerous industrial applications, for instance, flocculants, coagulants, rheology modifiers, dispersants, superabsorbents and binders. Of particular importance are high molecular weight water soluble polymeric flocculants which may be used as retention or drainage aids in paper making or to flocculate sludges such as sewage sludge, waste waters, textile industry effluents red mud from the Bayer Alumina process and suspensions of coal tailings etc.
• water soluble or water swellable polymers by polymerising water soluble monomers using a suitable initiator system.
• the polymers are usually provided either as a solid particulate product or as a reverse phase dispersion or emulsion.
• particulate polymers are prepared introducing initiators into an aqueous solution of the monomers and polymerising to form a polymer gel which is then cut into smaller pieces, dried and then ground to the appropriate particle size.
• the polymers are produced as beads by suspension polymerisation or as a water-in-oil emulsion or dispersion by water-in-oil emulsion polymerisation, for example according to a process defined by EP-A-150933, EP-A-102760 or EP-A-126528.
• water soluble and water swellable polymers can be prepared using many of the commercially available initiator systems, it is often difficult to prepare on an industrial scale polymers which have the correct molecular weight in combination with other desired characteristics, such as solubility, degree of absorbency etc. Over the last ten to fifteen years it has also become increasingly important to provide polymers which have extremely low levels of residual free monomer. This is particularly the case for polymers based on acrylamide monomer.
• WO-A-97 29136 describes an amidase enzyme which is particularly effective at high temperatures and thus can be applied to the hot polymer gel substantially immediately prior to the drying stage.
• this enzyme has shown particular advantages over other known amidases, it is still nonetheless difficult to consistently achieve low residual levels of acrylamide on an industrial scale.
• step (b) effecting polymerisation by subjecting the aqueous mixture formed in step (a) to polymerisation conditions to form a polymer of said monomer or monomer blend, wherein ultra violet initiator is distributed throughout the polymer,
• step (c) subjecting the polymer formed in step (b) to ultra violet light radiation, characterised in that the polymerisation step (b) is conducted substantially in the absence of ultra violet radiation.
• step (c) is conducted using fairly low levels of ultra violet radiation intensity, for instance up to 1 Watt/cm 2 , usually below 500 milli Watts/cm 2 .
• step (b) effecting polymerisation by subjecting the aqueous mixture formed in step (a) to polymerisation conditions to form a polymer of said monomer or monomer blend,
• step (c) subjecting the polymer formed in step (b) to ultra violet light radiation at an intensity of up to 500 milli Watts,
• the advantage of being able to use relatively low levels of radiation intensity is that there is a reduced risk of inducing denaturing of the polymer.
• One effect of denaturing the polymer may be undesirable or uncontrolled cross-linking or unacceptable loss of solubility. This may be particularly important when preparing high molecular weight water soluble polymers, where cross-linking and/or loss of solubility could have a deleterious effect on performance.
• To a certain extent exposure to high levels of ultra violet radiation may be detrimental to deliberately cross-linked polymers in that the additional cross-linking would be uncontrolled and could also lead to a loss of performance.
• excessive exposure to ultra-violet cross-linking may result in excessive cross-linking which could impair the absorbency charactersitics.
• UV radiation intensity is used, for instance up to 100 milli Watts/cm 2 .
• levels of intensity will be above 5 or 10 milli Watts/cm 2 .
• Intensities of below 50 milli Watts/cm 2 are generally preferred, for instance in the range of 30 to 40 milliWatts/cm 2 .
• the water soluble or water swellable polymer is prepared by polymerisation of a water soluble monomer or water soluble monomer blend.
• water soluble we mean that the water soluble monomer or water soluble monomer blend has a solubility in water of at least 5 g in 100 ml of water, measured at 25° C.
• the polymerisation step (b) may employ conventional polymerisation techniques, provided that these do not result in exposure to ultra violet light.
• the polymerisation step (b) may be effected by subjecting the aqueous monomer solution to any conventional polymerisation conditions which do not involve exposure to ultra violet radiation. Desirably this may be achieved by the use of redox initiators and/or thermal initiators.
• redox initiators include a reducing agent such as sodium sulphite, sulphur dioxide and an oxidising compound such as ammonium persulphate or a suitable peroxy compound, such as tertiary butyl hydroperoxide etc.
• Redox initiation may employ up to 10,000 ppm (based on weight of monomer) of each component of the redox couple.
• each component of the redox couple is often less than 1000 ppm, typically in the range 1 to 100 ppm, normally in the range 4 to 50 ppm.
• the ratio of reducing agent to oxidizing agent may be from 10:1 to 1:10, preferably in the range 5:1 to 1:5, more preferably 2:1 to 1:2, for instance around 1:1.
• Polymerisation step (b) may also be effected by employing a thermal initiatior alone or in combination with other initiator systems, for instance redox initiators.
• Thermal initiators would include any suitable initiator compound that releases radicals at an elevated temperature, for instance azo compounds, such as azobisisobutyronitrile (AZDN), 4,4′-azobis-(4-cyanovalereic acid) (ACVA).
• AZDN azobisisobutyronitrile
• ACVA 4,4′-azobis-(4-cyanovalereic acid)
• thermal initiators are used in an amount of up 10,000 ppm, based on weight of monomer. In most cases, however, thermal initiators are used in the range 100 to 5,000 ppm preferably 200 to 2,000 ppm, usually around 1,000 ppm.
• the water soluble or water swellable polymer prepared according to the process of the present invention may be cationic, anionic, nonionic or amphoteric. It may be substantially linear or alternatively branched or cross-linked.
• Cross-linked or branched polymers are prepared by incorporating a branching or cross-linking agent into the monomer blend.
• the cross-linking or branching agent may be for instance a di- or multifunctional material that reacts with functional groups pendant on the polymer chain, for instance multivalent metal ions or amine compounds which can react with pendant carboxylic groups.
• the cross-linking or branching agent will be a polyethylenically unsaturated compound, which becomes polymerised into two or more polymer chains.
• cross-linking agents include methylene-bis-acrylamide, tetra allyl ammonium chloride, triallyl amine and polyethylene glycol di acrylate.
• the polymers may be highly crosslinked and therefore water insoluble but water swellable.
• the polymer may be water soluble and either substantially linear or slightly branched, for instance prepared using less than 10 ppm cross-linking/branching monomer.
• the water soluble or water swellable polymer may be cationic, anionic, amphoteric or non-ionic.
• Anionic polymers may be formed from one or more ethylenically unsaturated anionic monomers or a blend of one or more anionic monomers with for instance a nonionic monomer, preferably acrylamide.
• the anionic monomers include acrylic acid, methacrylic acid, maleic acid, crotonic acid, itaconic acid, vinylsulphonic acid, allyl sulphonic acid, 2-acrylamido-2-methylpropane sulphonic acid and salts thereof.
• a preferred anionic polymer is the copolymer of sodium acrylate with acrylamide.
• Cationic polymers may be formed from one or more ethylenically unsaturated cationic monomers optionally with for instance a nonionic monomer, preferably acrylamide.
• the cationic monomers include dialkylamino alkyl (meth) acrylates, dialkylamino alkyl (meth) acrylamides, including acid addition and quaternary ammonium salts thereof, diallyl dimethyl ammonium chloride.
• Preferred cationic monomers include the methyl chloride quaternary ammonium salts of dimethylamino ethyl acrylate and dimethyl aminoethyl methacrylate.
• Amphoteric polymers include at least one cationic monomer (for example as defined above) and at least one anionic monomer (for example as defined above) optionally with a nonionic monomer, especially acrylamide.
• Non-ionic polymers include polymers of any suitable non-ionic monomers, for instance, acrylamide, methacrylamide, N-vinylpyrrolidone and 2-hydroxyethyl acrylate.
• Preferred non-ionic polymers comprise acrylamide especially acrylamide homopolymers.
• the water soluble or water swellable polymers comprise acrylamide.
• the polymer produced by the process of the present invention may be a relatively low molecular weight polymer, for instance polymerised to a molecular weight below 100,000, for instance 2,000 to 10,000.
• the polymers are relatively higher molecular weight, for instance at least 100,000, especially at least 500,000.
• the polymer has a molecular weigh in the range of above 1 million to 20 or 30 million or higher.
• these high molecular weight polymers tend to exhibit high intrinsic viscosities (IV), for instance at least 3 dl/g (measured at various polymer concentrations using standard techniques in 1 N NaCl buffered to pH 7.5 at 25° C.).
• the polymer has an IV of at least 4 dl/g often at least 7 or 8 dl/g, for instance at least 12 dl/g. In some cases it may be highly desirable for the polymer to have an IV as high as 20 or 30 dl/g or even higher. However especially preferred polymers have an IV in the range 8 to 18 dl/g.
• an aqueous solution of water soluble monomer may be polymerised by solution polymerisation to provide an aqueous gel or by reverse phase polymerisation in which an aqueous solution of monomer is suspended in a water immiscible liquid and polymerised to form polymeric beads or alternatively by emulsifying aqueous monomer into an organic liquid and then effecting emulsion polymerisation.
• reverse phase polymerisation examples of reverse phase polymerisation are given in EP-A-150933, EP-A-102760 or EP-A-126528.
• the polymer is prepared by solution polymerisation.
• the process of the present invention requires that an aqueous monomer mixture is first formed comprising (i) a water soluble ethylenically unsaturated monomer or blend of monomers and (ii) an ultra violet initiator.
• the aqueous monomer mixture may also contain other components, for instance redox initiators or thermal initiators or other compounds that may assist with the polymerisation step (b).
• the aqueous monomer mixture may also comprise other ingredients, for instance chain transfer agents which may be required to regulate the chain length.
• the ultra violet initiator (ii) comprised in the aqueous monomer mixture may be any suitable initiator that remains substantially inert during the polymerisation step (b). Therefore the ultra violet initiator would generally be unsuitable if it decomposed during this initial polymerisation step. Therefore it is desirable to choose an ultra violet initiator that is not temperature sensitive at a temperature reached during the initial polymerisation step.
• the ultra violet initiator is distributed homogenously throughout the aqueous monomer mixture, in order that it is evenly distributed throughout the resulting polymer.
• the ultra violet initiator is soluble or dispersible in the aqueous monomer or monomer blend.
• the ultra violet initiator is a compound of formula:
• R 1 and R 2 are each independently C 1-3 alkyl or together form a C 4-8 cycloaliphatic ring, R 3 is H, C 1-2 alkyl or —O(CH 2 CH 2 ) n OH and n is 1-20.
• An especially preferred ultra violet initiator is the compound defined by the formula,
• Another especially preferred UV initiator is the compound of the formula
• the ultra violet initiator is used in an amount up to 10,000 ppm by weight of monomer. However, for economic reasons it is usually preferred not to use more than about 5,000. Suitable results are often obtained when the ultra violet initiator is included in an amount in the range 50 to 3,000 ppm, more preferably 100 to 2,500 ppm, especially 500 to 2,000 ppm.
• the process involves the step of subjecting the polymer formed in the polymerisation step (b) to ultra violet radiation.
• This may be done by passing the formed polymer under ultra violet lamps.
• the polymer may be passed from the reactor vessel and then irradiated with a suitable dose of ultra violet light and then passed to a drying section.
• the polymer may be exposed to ultra violet radiation in the reactor vessel.
• the polymer is subjected to the ultraviolet light in the drying section.
• ultra violet lamps are mounted such that the polymer is exposed to ultra violet light whilst inside the drying equipment. More preferably the drying equipment is a fluid bed dryer and the ultra violet lamps are mounted inside the dryer.
• a further aspect of the invention we provide a method of reducing the residual monomer content in a water soluble or water swellable polymer by subjecting the polymer to ultra violet irradiation in the presence of an ultra violet initiator.
• the ultra violet initiator may be applied to the surface of the formed polymer and allowed to coat the surface of the polymer particles and then subjecting the polymer to ultra violet radiation.
• the ultra violet initiator is actually absorbed into the polymer and is then preferably distributed throughout the polymer before being subjected to irradiation by ultra violet light.
• the water soluble or water swellable polymer may be formed containing the ultra violet initiator distributed throughout the polymer. This may be for instance as a result of carrying out a process in accordance with the first aspect of the invention.
• the method of reducing residual monomer is applied to polymers of acrylamide and said acrylamide polymer contains residual acrylamide monomer.
• the polymer of acrylamide is a relatively high molecular weight polymer and has an intrinsic viscosity of at least 4 dl/g, often at least 7 or 8 dl/g, for instance at least 12 dl/g.
• polymers of acrylamides which have an IV in the range 8 to 18 dl/g.
• the ultra violet initiator may be any suitable ultra violet initiator as given herein before. It is preferred that the ultra violet initiator is water soluble or at least water dispersible. Preferably the ultra violet initiator is a compound of formula,
• R 1 and R 2 are each independently C 1-3 alkyl or together form a C 4-8 cycloaliphatic ring
• R 3 is H, C 1-2 alkyl or —O(CH 2 CH 2 ) n OH and n is 1-20.
• the ultra violet initiator either a compound of formula,
• aqueous monomer mixture comprising 90% by weight acrylamide and 10% by weight dimethylaminoethyl acrylate methyl chloride quaternary ammonium salt and having a total monomer concentration of about 30%. Nitrogen gas is passed through the aqueous medium in order to remove dissolved oxygen or other volatile reactive species. 4.5 ppm potassium bromate KBrO 3 and 9 ppm sodium sulphite Na 2 SO 3 is combined with the aqueous monomer and mixed thoroughly. Polymerisation is allowed to proceed for two hours and the resulting polymer is dried using a fluid bed dryer.
• Examples 1 to 6 are repeated but using a an aqueous solution of acrylamide monomer. Viscosity and residual acrylamide concentrations are shown in Table 2. TABLE 2 UV UV Residual initiator irradiation 1% solution Acrylamide Test (ppm) (min) viscosity (cP)# (ppm) 1 0 0 28 532 2 0 20 24 412 3 500 0 26 552 4 500 20 24 38 5 2000 0 28 639 6 2000 20 24 32

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