Surface charge of polymer particles in water: the role of ionic end-groups

Polymer particles, containing macromolecules made by the polymerization of nonionic monomers, can be ionized in water thanks to the end-groups of the macromolecules. We show that poly(methylmethacrylate) particles with ionic end-groups can acquire colloidal properties such as dispersion metastability and electrokinetic mobility. We demonstrate that the variation of these colloidal properties according to solution pH is uniquely determined by the chemical nature of the end-groups and therefore by the nature of the initiator used in the polymerization reaction. We compare polymer dispersions in which the polymer particles were made by different processes (e.g., surfactant-free emulsion polymerization or precipitation of the macromolecules induced by solvent shifting). For each colloidal dispersion, we determine the number of end-groups that are actually located at the surfaces of the particles, and we show that this number is a trace of the process by which the macromolecules were self-assembled into colloidal particles. We propose that it is possible to recover mechanistic details of this self-assembly process through measurements of the distribution of end-groups within the particles.