Anionic-cationic polyion complexes comprising zwitterionic monomer component

A process for forming a water swollen gel of a polyion complex by

• i) providing an aqueous solution containing 1 to 50% by weight of a cationic polymer having an overall cationic charge obtained by polymerising ethylenically unsaturated monomers comprising
• a) 5 to 100 mole % cationic monomer having a cationic or cationisable group;
• b) 0 to 85 mole % zwitterionic monomer having a pendant zwitterionic group;
• and
• c) 0 to 85 mole % nonionic monomer;
• ii) providing an aqueous solution containing 1 to 50% by weight of an anionic polymer having an overall anionic charge obtained by polymerising ethylenically unsaturated monomers including:
• d) 5 to 100 mole % anionic monomer having an anionic or anionisable group;
• e) 0 to 85 mole % zwitterionic monomer having a zwitterionic group;
• and
• f) 0 to 80 mole % nonionic monomer;
• iii) mixing the aqueous solution of anionic polymer and the aqueous solution of cationic polymer to form a polyion complex in amounts such that the total units in the polyion complex derivable from nonionic monomer c and f is in the range 0 to 60 mole %, the total mole % of units in the polyion complex derivable from zwitteronic monomer is in the range 1 to 70 mole %, and the ratio of moles of excess anionic or anionisable groups in the anionic polymer to the moles of excess cationic or cationsable groups in the cationic polymer is in the range 1.5:1 to 1:1.5, whereby a water-swollen gel of the polymer complex is formed, having up to ten parts by weight water from either the cationic polymer-containing aqueous solution, the anionic polymer-containing aqueous solution or both per part by weight total polymer, and if the cationic polymer-containing aqueous solution contains 0 mole % zwitterionic monomer, then the anionic polymer-containing aqueous solution contains zwitterionic monomer in an amount sufficient to provide a total mole % of units in the polyion complex derivable from zwittionic monomer in the range of 1 to 70 mole %, and if the anionic polymer-containing aqueous solution contains 0 mole % zwitterionic monomer, then the cationic polymer-containing aqueous solution contains zwitterionic monomer in an amount sufficient to provide a total mole % of units in the polyion complex derivable from zwitterionic monomer in the range of 1 to 70 mole %.