Polymer semiconductor (PSC) is the foundation for building soft and stretchable electronic devices with complex functionalities like signal amplifiers, filters, and switches. Despite recent progress in achieving PSC charge transport maintenance under a single stretching event, elasticity (i.e., mechanical reversibility) remains a major issue. For realistic consumer electronics, PSC needs to function through repeated stretching-releasing cycles. My Ph.D. research in Prof. Zhenan Bao's lab addressed the challenge by rationally designing azide-terminated polybutadiene molecular precursors that can undergo self-crosslinking and crosslinking with PSCs in a finely controlled ratio leveraging the encoded reactivity difference. Additionally, taking advantage of the composite semiconductor's photo-patternability and the approach's general applicability to p- and n-type PSC, we demonstrated the compatibility of our materials with solution-processed multilayer circuits manufacturing. 

Environmental instability is the long-standing challenge retarding the clinical translation of soft electronics. Previous methods are mainly focused on encapsulation of the entire device with stretchable polymer coatings, which usually have high water permeability and thus exhibit poor protection effects due to large free volume. To address the challenge, I developed a molecular protecting method that significantly improves PSC’s stability in transistors that operate in harsh environments (humid air, water, and sweat). This involves the covalent functionalization of fluorinated molecules onto the PSC film surface to form densely packed nanostructures with a remarkable ability to block water absorption and diffusion. The nanostructured encapsulation exhibits orders of magnitude lower water permeability than that of current encapsulation materials used for stretchable electronic devices, while maintaining its morphology and protecting function even under mechanical deformation. 

From a general perspective, a polymer network is a space-spanning collection of strands held together by junctions. The mechanochemical responses of physical or chemical bonds are central to dictating macroscopic mechanical behaviors. However, such understanding remains fundamentally challenging due to the complex interplay between junction and strand dynamics and historical limitations on our ability to measure molecular states of polymer networks under deformation. These limitations impact not only experimental designs but also theory development. My postdoc research in Prof. Bradley Olsen's lab made a large advancement by applying a custom-built optical-mechanical characterization tool to see and quantify bond dissociation under shear. Enabled by rational molecular designs, we develop a new polymer system and obtain substantial fundamental insights into the effects of junction functionality and chemical kinetics on mechanochemical responses of labile bonds and corresponding network topological evolution under deformation. The obtained understanding can be broadly leveraged to advance the inverse design of materials with desired structural dynamics and rheological behaviors.