Design of Mixed-Graft Block Copolymers for Emerging Applications

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PART 1: NON-TECHNICAL SUMMARYOrganic polymers have been widely adopted as functional or structural materials due to their diverse properties and facile processability. While there is great demand for developing single polymeric materials with more than one independently-tunable property for the fabrication of next-generation electronic and energy devices, scientific challenges remain. This project aims to introduce graft-copolymers -- molecules containing a polymer backbone tethered with multiple side chains -- as a synthetic platform to realize organic materials in which the dependencies of several properties are decoupled. Examples of such properties include ion-/electron-conductivity, nanostructures, and mechanical properties. The ability to independently tune multiple properties is enabled by the unique molecular architecture of graft-copolymers with diverse chemical compositions and structural parameters that can be precisely controlled. Tuning the backbone length of these polymers opens a way not only to enabling the formation of ultrasmall nanodomain spacing but also to realizing desirable thermomechanical properties and processability. The proposed materials are closely relevant to emerging applications such as electronic skin and components in soft robotics.PART 2: TECHNICAL SUMMARYThe overall goal of this project is to develop processable and mechanically compliant polymeric materials with both ionic and electronic conductivities that can be independently tuned and oriented. Mixed-graft block copolymers (mGBCPs) consisting of two or more types of functional polymeric side chains grafted on a linear backbone will be designed and synthesized to achieve this goal. The incompatibility of distinct side chains of mGBCPs results in phase-separation to form ordered nanostructures with the backbone serving as the interface. A diverse range of side chain functionalities that are responsible for different conductive properties are respectively enriched in different nanodomains. The orientation of the conductive phases can be regulated through directed self-assembly techniques, and the nanodomain sizes are controlled primarily by the side chains lengths. Tuning the backbone length of mGBCPs opens a way not only to enabling the formation of ultrasmall nanodomain spacing but also to realizing desirable thermomechanical properties and processability. This project tackles a grand challenge in the application of classic linear block copolymers in which the bulk properties and nanostructures cannot be independently tuned due to their mutual compositional dependence.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.