Accessing Complex Nanoscale Packing with Aba' Triblock Copolymers

Formed by combining chemically distinct polymer blocks, block copolymers are used across several industries owing to their ability to self-assemble at the nanoscale. Of particular interest in recent years has been the discovery that these ostensibly simple materials can order into micelles arranged on large, complex Frank–Kasper (FK) lattices. Frank–Kasper (FK) phase formation in diblock copolymer melts is largely based on three parameters: block volume fraction, molecular weight, and conformational asymmetry. Less explored, however, is how their formation can be driven in triblock copolymers. This research studies this question with a particular focus on ABAʹ triblock copolymers with variable core (A) block lengths. We hypothesize that an asymmetry in the core block lengths will open up a FK phase window. Polymers will be synthesized by ruthenium-mediated ring-opening metathesis polymerization (ROMP). Volume fraction and core block length asymmetry will be varied to yield symmetric and asymmetric triblock copolymers. Polymers will then be characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR) and size exclusion chromatography (SEC). Following, small angle X-ray scattering (SAXS) will be used to assess polymer nanostructure and determine order–disorder and order–order transitions.