Title: Electrostatic Compatibilization of Polymers

Abstract: The mixing of chemically dissimilar polymers (i.e., polymer blending) is an attractive route to create hybrid materials with useful and tunable physicochemical properties. Importantly, it provides a practical solution to bypass the expensive sorting step to further improve the recycling rate of plastic waste. Yet, many polymer blends exhibit poor material properties due to thermodynamic immiscibility, hindering its current implementation as a recycling strategy. Hence, the compatibilization of immiscible polymer blends is essential to generate materials with improved performance. Electrostatic interactions in low dielectric polymer media facilitate polymer blend compatibilization through strong, attractive bonds that overcome chain repulsion. While this compatibilization strategy has been previously shown to be effective, there is a limited understanding in controlling the phase behavior and macroscopic properties of sparsely charged, compatibilized blends. Moreover, counterion free ionic bond formation strategies during electrostatic blending are currently limited to acid-base proton transfers.

This work employs model systems to explore polymer design parameters that directly influence material properties upon electrostatic blend compatibilization. First, control over blend microstructure and rheological properties is achieved through charge density manipulation in pendant functionalized polymer blends. The functionalization of an immiscible poly(acrylate)/poly(siloxane) blend with sparse 1.0 and 6.5 mol% pendant ionic bonds generated by sulfonic acid to tertiary amine proton transfers results in optically clear and compatibilized materials. An increase in ionic content promotes a higher level of chain mixing and reduces microstructural ordering, thereby affecting viscoelastic behavior. Second, charge placement along a polymer backbone impacts blend properties. Model poly(styrene) and poly(methyl acrylate) are functionalized with either a block or random distribution of sulfonic acid and tertiary amine groups respectively at a constant 5 mol% functionality and volumetric degree of polymerization. Consistent with theoretical predictions, while the purely random blend is disordered, blends containing a blocky component exhibit microphase separated structures. The type of microstructure directly correlates with charge placement to influence thermal and viscoelastic properties.

Additionally, this work explores the use of sulfonate ester chemistries to generate ionic bonds during polymer blending. Quaternization of tertiary amines with alkyl sulfonates, either at the chain-end or through sparse 1 mol% pendant functionalization, produces highly compatibilized poly(acrylate)/poly(siloxane) blends exhibiting unique microphases. This chemistry proceeds under solution- and melt-state conditions, and the rate of ionic bond formation is dependent on the migrating alkyl group and local steric environment.

Overall, these findings establish the design of tailored polymer blends using an expanded chemistry toolkit and further highlight electrostatic blend compatibilization as a promising recycling strategy.