Patent ID: 6841639

Claim:
A polymerisation process conducted in a reaction vessel in which ethylenically unsaturated monomers consisting substantially only of: a) 1 part by mole zwitterionic monomer of the general formula I in which n is 2 to 24; m is 0 to 20; of the groups R 1 , one may be methyl or hydrogen and the rest are all hydrogen; and X is a zwitterionic group; and b) 1 to 10 parts by mole hydrophobic comonomer of the general formula II in which p is 1 to 24; are copolymerised in solution in a solvent system in which the monomer mixture and the polymer are soluble and which comprises at least one solvent; comprising the steps: adding said at least one solvent to the reaction vessel; adding a radical initiator to the reaction vessel; feeding the monomers constantly over a monomer feed phase into the reaction vessel under conditions at which polymerisation takes place, at a predetermined monomer feed rate whereby the molar ratio of zwitterionic monomer to hydrophobic comonomer in the reaction vessel is maintained substantially constant (±10%) throughout the monomer feed phase; and polymerising the monomers to produce zwitterionic polymer product.