Supramolecular Assembly of End-Functionalized Polystyrene and Polydimethylsiloxane with Hybrid Nanostructures

Blends of oppositely charged polymers are capable of self-assembling into well-ordered nanostructures via supramolecular self-assembly. A series of monosulfonated-terminated polystyrene (PS) and monopiperidine-terminated poly-(dimethylsiloxane) (PDMS) polymers with different molecular weights were synthesized and blended to investigate their phase behavior. A new synthetic route for piperidine-terminated PDMS with low dispersity and high end-group fidelity was developed based on a functionalized initiator accessible from commercially available reagents and compatible with anionic ring-opening polymerization. The resulting nanostructure of the blends was measured via small-angle X-ray scattering (SAXS) performed across a range of temperatures and revealed disordered structures in blends prepared with low molecular weight polymers. A model derived by Tanaka using the random phase approximation (RPA) was applied to extract the heteroassociation fraction (z) and effective interaction parameter (χ_eff), and a quantitatively similar value of z was observed across all blends with disordered morphologies. High molecular weight blends exhibited a variety of hybrid ordered nanostructures, and by precisely tuning the mixing ratio, we were able to induce phase transitions and achieve a variety of ordered nanostructures with long-range order. A molecular-scale mechanism to balance the electrostatic strength of end group association and segregation strength between the constituent polymers is proposed to rationalize the observed phase behavior.