Process for the production of water-absorbing compositions

Abstract

A process for producing a copolymer of an α,β-unsaturated monomer having at least one pendant unit selected from a carboxylic acid group and derivatives thereof, and a copolymerizable monomer is described in which the process is carried out in a single solvent which is particularly an aromatic solvent. Processes of controlling the reaction and the particle size of the polymer produced are also described.

1 . A process for producing a copolymer of an α, β-unsaturated monomer having at least one pendant unit selected from a carboxylic acid group and derivatives thereof, and a copolymerisable monomer comprising the steps of copolymerizing the monomers in solution in a single solvent.  
     
     
         2 . A process according to  claim 1  wherein the solvent is an aromatic solvent.  
     
     
         3 . A process according to  claim 2 , wherein the aromatic solvent is benzene or a substituted benzene.  
     
     
         4 . A process according to  claim 3 , wherein the aromatic solvent is toluene.  
     
     
         5 . A process for producing a water-absorbent composition comprising the steps of producing a copolymer of an α, β-unsaturated monomer having at least one pendant unit selected from a carboxylic acid group and derivatives thereof, with a copolymerisable monomer in accordance with the process of any one of  claims 2  to  4 , removing the aromatic solvent and partially neutralizing at least a portion of the carboxylic acid groups; and allowing the resultant copolymer to cure, optionally in the presence of a cross-linking agent.  
     
     
         6 . A process according to  claim 5  wherein the removal of the aromatic solvent and partial neutralization comprise the steps of separating the copolymer from the reaction mixture by filtration, driving off the aromatic solvent to leave a dry powder, and dissolving the powder in an aqueous solution of the neutralization agent such that it is partially neutralised.  
     
     
         7 . A process according to  claim 5  wherein the removal of the aromatic solvent and partial neutralization comprise the steps of adding the aqueous neutralization agent to a slurry of the copolymer in the aromatic solvent and removing the aromatic solvent by distillation.  
     
     
         8 . A process according to  claim 5  wherein the removal of the aromatic solvent and partial neutralization comprise the steps of injecting steam into the slurry of the polymer in the organic solvent in the presence of the aqueous neutralization agent or injecting steam into the slurry and subsequently adding the aqueous neutralization agent.  
     
     
         9 . A process according to  claim 5  wherein the removal of the aromatic solvent and partial neutralization comprise the steps of adding the aqueous neutralization agent to the slurry of the copolymer in the aromatic solvent and carrying out a phase separation to obtain the polymer in the aqueous layer.  
     
     
         10 . A process according to any one of  claims 5  to  9  additionally comprising the step of concentrating the aqueous solution of the polymer.  
     
     
         11 . A process according to any one of  claims 5  to  10  wherein the aqueous neutralization agent is an aqueous solution of sodium hydroxide.  
     
     
         12 . A process according to any one of  claims 5  to  11  wherein curing is achieved by reaction with an external crosslinker for the copolymer.  
     
     
         13 . A solution of an α, β-unsaturated monomer having at least one pendant unit selected from a carboxylic acid group and derivatives thereof, and a copolymerisable monomer in a solvent comprising an aromatic solvent.  
     
     
         14 . A solution according to  claim 13 , wherein the aromatic solvent is benzene or a substituted benzene.  
     
     
         15 . A solution according to  claim 14 , wherein the aromatic solvent is toluene.  
     
     
         16 . A solution according to any one of  claims 13  to  15  additionally including a polymerisation initiator.  
     
     
         17 . A process for producing a copolymer of an α, β-unsaturated monomer having at least one pendant unit selected from a carboxylic acid group and derivatives thereof, with a copolymerisable monomer comprising reacting the α, β-unsaturated monomer with the copolymerisable monomer in a reaction vessel and controlling the reaction temperature by one or more of: 
 (A) controlling the addition rate of at least one of the reaction components, including a solvent;  
 (B) allowing evaporative cooling to occur within the reaction vessel;  
 (C) controlling the concentration and temperature of the feed to the reaction vessel;  
 (D) using the heat of the reaction to heat incoming reactants to reaction temperature; and  
 (E) precharging a seed amount of at least one of the monomers to the reaction vessel.  
 
     
     
         18 . A process according to  claim 17  wherein the reaction temperature is controlled by controlling the addition rate of at least one of the monomers.  
     
     
         19 . A process according to  claim 17  or  18  wherein the solvent is an organic solvent.  
     
     
         20 . A method of controlling the particle size of the polymer produced in the reaction of a copolymer of an α, β-unsaturated monomer having at least one pendant unit selected from a carboxylic acid group and derivatives thereof, with a copolymerisable monomer comprising reacting the α, β-unsaturated monomer with the copolymerisable monomer in a reaction vessel and controlling the addition rate of at least one of the reaction components.  
     
     
         19 . A process according to  claim 17  wherein the solvent is an organic solvent.  
     
     
         20 . A method of controlling the particle size of the polymer produced in the reaction of a copolymer of an α, β-unsaturated monomer having at least one pendant unit selected from a carboxylic acid group and derivatives thereof, with a copolymerizable monomer comprising reacting the α, β-unsaturated monomer with the copolymerizable monomer in a reaction vessel and controlling the addition rate of at least one of the reaction components.  
     
     
         21 . A process for producing a water-absorbent composition which comprises: 
 (a) copolymerizing an α, β-unsaturated monomer having at least one pendant unit selected from a carboxylic acid group and derivatives thereof and a copolymerizable monomer in a reaction zone in a single aromatic solvent;    (b) removing the aromatic solvent and partially neutralizing at least a portion of the carboxylic acid groups; and    (c) allowing the resultant copolymer to cure, optionally in the presence of a cross-linking agent.    
     
     
         22 . A process according to  claim 21  wherein said process comprises copolymerizing said monomers by free radical polymerization involving the use of an initiator.  
     
     
         23 . A process according to  claim 22  wherein the monomers and initiator are soluble in aromatic solvent and the copolymer is insoluble in the aromatic solvent.  
     
     
         24 . A process according to  claim 21  wherein said copolymer has a peak molecular weight of greater than or equal to 5000.  
     
     
         25 . A process according to  claim 21  wherein said process comprises supplying the monomers separately to the reaction zone and controlling the addition rate of the monomers to the reaction zone.  
     
     
         26 . A process according to  claim 21  wherein the aromatic solvent is benzene or a substituted benzene.  
     
     
         27 . A process according to  claim 21  wherein the aromatic solvent is toluene.  
     
     
         28 . A process according to  claim 21  wherein step (b) comprises separating the copolymer from the reaction mixture by filtration, driving off the aromatic solvent to leave a dry powder and dissolving the powder in an aqueous solution of a neutralization agent.  
     
     
         29 . A process according to  claim 21  wherein step (b) comprises adding an aqueous neutralization agent to a slurry of the copolymer in the aromatic solvent and removing the aromatic solvent by distillation.  
     
     
         30 . A process according to  claim 21  wherein step (b) comprises injecting steam into a slurry of the polymer in the organic solvent in the presence of an aqueous neutralization agent or injecting steam into the slurry and subsequently adding the aqueous neutralization agent.  
     
     
         31 . A process according to  claim 21  wherein step (b) comprises adding an aqueous neutralization agent to a slurry of the copolymer in the aromatic solvent and carrying out a phase separation to obtain the polymer in the aqueous layer.  
     
     
         32 . A process according to  claim 21  additionally comprising the step of concentrating the aqueous solution of the polymer.  
     
     
         33 . A process according to  claim 21  wherein the aqueous neutralization agent is an aqueous solution of sodium hydroxide used as a neutralization agent.  
     
     
         34 . A process according to  claim 21  wherein curing is achieved by reaction with an external cross-linker for the copolymer.  
     
     
         35 . A process according to  claim 21  wherein the copolymerization reaction temperature is controlled by one or more of: 
 (i) controlling the addition rate of at least one of the reaction components, including the solvent;  
 (ii) allowing evaporative cooling to occur within the reaction vessel;  
 (iii) controlling the concentration and temperature of the feed to the reaction vessel;  
 (iv) using the heat of the reaction to heat incoming reactants to reaction temperature; and  
 (v) precharging a seed amount of at least one of the monomers to the reaction vessel.  
 
     
     
         36 . A process according to  claim 35  wherein the reaction temperature is controlled by controlling the addition rate of at least one of the monomers.  
     
     
         37 . A process according to  claim 35  wherein the solvent is an organic solvent.  
     
     
         38 . A process according to  claim 21  further including controlling the addition rate of at least one of the reaction components to control the particle size of the polymer produced in the reaction.  
     
     
         39 . A process according to  claim 21  characterized in that the unsaturated monomer contains carboxylic acid anhydride groups.  
     
     
         40 . A process according to  claim 21  characterized in that the unsaturated monomer is maleic anhydride.  
     
     
         41 . A process according to  claim 21  characterized in that the copolymerizable monomer is selected from isobutylene and styrene.