We report the synthesis of sterically-stabilized diblock copolymer particles at 20% w/w solids via RAFT aqueous dispersion polymerization of N,N-dimethylacrylamide (DMAC) in highly salty media (2 M (NH4)2SO4). This is achieved by selecting a well-known salt-tolerant zwitterionic water-soluble polymer, poly(2-(methacryloyloxy)ethyl phosphorylcholine), to act as the soluble precursor block. A relatively high degree of polymerization (DP) can be targeted for the salt-insoluble block, which produces a turbid free-flowing dispersion by a steric stabilization mechanism. Particle characterization techniques include dynamic light scattering (DLS) and electrophoretic light scattering (ELS) using a state-of-the-art instrument that is capable of accurate measurements in concentrated salt solutions. Subsequent dilution using deionized water lowers the background salt concentration and hence causes in situ molecular dissolution of the salt-intolerant PDMAC chains, which leads to a substantial thickening effect and the formation of transparent gels. Thus this new PISA formulation enables high molecular weight water-soluble polymers to be prepared in a highly convenient, low-viscosity latex-like form. In principle, such aqueous PISA formulations are highly attractive: there are various commercial applications for high molecular weight water-soluble polymers while the negative aspects of using a RAFT agent (i.e. its cost, color and malodor) are minimized when targeting such high DPs.

Synthesis of high molecular weight water-soluble polymers as low-viscosity nanoparticles by RAFT aqueous dispersion polymerization in highly salty media

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