Water-soluble post branched cationic acrylamide polymers and use thereof
A cationic copolymer is obtained by the Hofmann rearrangement (also referred to as the Hofmann degradation reaction) in aqueous solution in the presence of an alkaline-earth and/or alkali hydroxide and an alkaline-earth and/or alkaline hypohalide, on a base copolymer comprising at least one nonionic monomer selected from the group comprising acrylamide (and/or methacrylamide), N,N-dimethylacrylamide and/or acrylonitrile The copolymer is branched after the Hofmann rearrangement, in the presence of at least one polyfunctional branching agent, and is soluble in water.
1. A process for preparing a water-soluble cationic copolymer said process comprising the sequential steps of
(a) reacting a base copolymer comprising at least one nonionic monomer selected from the group consisting of acrylamide methacrylamide, N,N-dimethylacrylamide and acrylonitrile in aqueous solution in the presence of an alkaline-earth and/or alkali hydroxide and an alkaline-earth and/or alkaline hypohalide, and
(b) reacting with at least one polyfunctional branching agent.
2. A process according to claim 1 , wherein the polyfunctional branching agent is selected from the group consisting of:
polyisocyanates: hexamethylene diisocyanate,
polyhalides: 1,2-dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane and 1,6-dichlorohexane,
polyepoxides: polyethylene glycol diepoxides, ethylene glycol diglycidyl ether (EGDE), polyethylene glycol triepoxide,
alkylepoxy halides: epichlorohydrin, bischlorohydrin ethers of alkylene glycols and polyalkylene glycol,
alkylene carbonates: ethylene carbonate, propylene carbonate
and bischloroformates: 2,2-dimethylpropylene bischloroformate.
3. A process according to claim 1 , wherein the polyfunctional branching agent is water-soluble and selected from the group consisting of polyepoxides and alkylepoxy halides.
4. A process according to claim 1 , wherein the polyfunctional branching agent is introduced at the rate of less than 2% by weight of the weight of cationic polymer.
5. A process according to claim 1 , wherein the polyfunctional branching agent is introduced at the rate of 500 to 15000 ppm.
6. A process according to claim 1 , wherein the base copolymer additionally comprises at least one unsaturated cationic ethylenic comonomer selected from the group consisting of monomers of a dialkylaminoalkyl methacrylamide, a diallylamine, a dialkyldiallylamine and their quaternary ammonium salts.
7. A process according to claim 1 , wherein the base copolymer has been branched during or after its polymerization, in the presence of a branching agent selected from the group consisting of methylene bisacrylamide (MBA), polyallyl compounds, ethylene glycol diacrylate, polyethylene glycol dimethacrylate, diacrylamide, cyanomethylacrylate, vinyloxyethyl acrylate, vinyloxyethyl methacrylate, formaldehyde, glyoxal, glycidyl ether compounds, and epoxy compounds.
8. Cationic copolymer produced according to the process of claim 1 , wherein the copolymer has a cationic charge density higher than 3 meq/g.
9. Method for fabricating a sheet of paper or cardboard, wherein, before formation of said sheet from a fibrous suspension, the cationic copolymer according to claim 1 is added to the fibrous suspension.
10. Method according to claim 9 , wherein the cationic copolymer is reduced into the suspension at the rate of 500 g/to 2 kg per metric ton of slurry.
11. Method according to claim 9 , wherein the cationic copolymer is introduced into the suspension at the rate of between 800 g and 1.5 kg per metric ton of slurry.
12. Cationic copolymer produced according to the process of claim 1 , wherein the copolymer has an intrinsic viscosity higher than 0.8 dl/g.
13. Cationic copolymer produced according to the process of claim 1 , wherein the copolymer has an intrinsic viscosity higher than 1 dl/g.
14. Cationic copolymer produced according to the process of claim 1 , wherein the copolymer has a cationic charge density higher than 5 meq/g.
15. A process according to claim 1 , wherein the base copolymer additionally comprises at least one nonionic monomer selected from the group consisting of N-vinyl acetamide, N-vinyl formamide, N-vinylpyrrolidone and vinyl acetate.