Abstract: The invention provides a process for preparing an aqueous dispersion of water insoluble heteropolymeric particles comprising polymerising in an aqueous reaction medium ethylenically unsaturated monomers, said ethylenically unsaturated monomers comprising ionisable ethylenically unsaturated monomers and non-ionisable hydrophilic ethylenically unsaturated monomers, to form said heteropolymeric particles dispersed in said aqueous reaction medium, wherein the monomers in said reaction medium at any point in time comprise less than 5 weight % of ionisable ethylenically unsaturated monomer, wherein for at least a part of the polymerisation the monomers in said reaction medium have a composition which is maintained with an ionisable ethylenically unsaturated monomer content of from 0.

Abstract: The invention provides a method for preparing an aqueous dispersion of polymer particles comprising the following steps: (i) preparing a dispersion having a continuous aqueous phase, a dispersed organic phase comprising one or more ethylenically unsaturated monomers, and an amphiphilic RAFT agent as a stabiliser for said organic phase, and (ii) polymerising said one or more ethylenically unsaturated monomers under the control of said amphiphilic RAFT agent to form said aqueous dispersion of polymer particles, novel amphiphilic RAFT agents for use in this method, novel RAFT agents useful in making these amphiphilic RAFT agents and methods for their manufacture.