(373c) Orientation Control in Ternary Graft Block Copolymer Thin-Films

One potential application of block copolymers (BCPs) is in microelectronics, as BCP lithography can be used to form surface patterning with feature sizes down to several nanometers. Controlling the orientation of the BCP’s self-assembled nanodomains with respect to the substrate in thin-film self-assembly is necessary for lithography but remains a challenge. In this work, ternary graft block copolymers (GBCPs) were synthesized with the aim of enabling this control over the nanostructure orientation. The project was inspired by our previous work on Janus GBCPs, in which covalent preorganization of the block interface allowed for stable self-assembled nanostructures with ultra-small domain sizes and rapid self-assembly. Various directed self-assembly techniques in which the substrates are modified to manipulate the orientation of nanodomains have been extensively studied, but the ternary GBCP approach presented here instead aims to control thin-film orientation by appropriately engineering interfacial interactions through molecular design. We anticipate that one block will preferentially wet the substrate, leaving the other two blocks to form a phase-separated nanopatterned top surface. Compared to linear triblock copolymers or ternary miktoarm star polymers, the GBCP architecture may have several advantages that arise from the interface of the blocks being covalently linked and pre-organized, including minimized formation of kinetically trapped states and accelerated self-assembly kinetics. The ternary GBCPs were synthesized via copolymerization of three macromonomers, homopolymers end-functionalized with polymerizable groups, and several combinations of macromonomers were explored. Self-assembly of the ternary GBCPs has been characterized using X-ray scattering, electron microscopy, and differential scanning calorimetry.