Electrostatically Mediated Compatibilization of Immiscible Polymer Blends via a Quaternization Approach

Ionic interactions are of tremendous utility in the recycling of mixed plastic waste to form compatibilized blends with useful properties. Ionic bonds between polymer chains are formed by the reversible, counterion-free proton transfer process between acid- and base-containing polymers. Alternatively, the incomplete counterion release via a coacervation process upon solution mixing of polyanions and polycations allows for macrophase separation. Utilizing a highly incompatible model system of poly(methyl acrylate) and poly(dimethylsiloxane), we demonstrate the quaternization of tertiary amines with alkyl sulfonates as a novel ionic bond formation strategy. These counterion-free polymer blends are compatibilized by strong ionic bonds that overcome the large enthalpy of mixing that drives macrophase separation. We explore this strategy at low levels of functionalization (e.g., 1 mol% pendant groups, and terminal group). High levels of compatibilization are achieved upon quaternization, where the macrophase separated domains in the initially turbid mixtures are substantially decreased to the nanoscale as elucidated by small-angle X-ray scattering. This work opens opportunities to understand the interplay between the ionic bond formation mechanism and resulting blend properties relevant for mixed plastic waste recycling.