Jerrick Edmund

Diblock copolymers consist of two distinct homopolymer blocks that are covalently linked. Research, including self-consistent field theory and experimental observations, have shown that linear diblock copolymers self-assemble into equilibrium nanostructure morphologies, including spherical, cylindrical, gyroid, and lamellar phases, as a function of block volume fraction, molecular weight, and temperature-dependent Flory-Huggins interaction parameter. Formation of the gyroid phase, a three-dimensional (3D) mesoscale network morphology, is of great interest due to the interpenetrating domain networks that can be used in a myriad of applications, including as separation membranes and therapeutic delivery vehicles. However, the narrow phase compositional window over which this network structure forms limits its uses. Increasing the block self-concentration along with conformational asymmetry based on the block statistical segment lengths, is hypothesized to expand the range of compositions associated with triply periodic 3D networks. In this work, three distinct architecturally asymmetric diblock copolymers of various compositions and molecular weights were synthesized through graft-through ring-opening metathesis polymerization of norbornene-based macromonomers. Conformational asymmetry was systematically increased by increasing the side chain length in one block while maintaining the other as a linear chain. Proton nuclear magnetic resonance spectroscopy and size-exclusion chromatography were used to determine the polymer molecular weight, dispersity, and volume fraction. Small-angle X-ray scattering was employed to characterize the morphologies formed by each polymer as a function of temperature. These measurements confirmed that these architecturally asymmetric diblock copolymers form a gyroid phase, dependent on the side chain length and overall molecular weight.