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C–H functionalization of commodity polyolefins affords functional materials derived from a high‐volume, low‐cost resource. However, current postpolymerization modification strategies result in randomly distributed functionalization along the length of the polymer backbone, which has a negative impact on the crystallinity of the resultant polymers, and thus the thermomechanical properties. Here, we demonstrate an amidyl radical mediated C–H functionalization of polyolefins to access blocky microstructures, which exhibit a higher crystalline fraction, larger crystallite size, and improved mechanical properties compared to their randomly functionalized analogues. Taking inspiration from the site‐selective C–H functionalization of small molecules, we leverage the steric protection provided by crystallites and target polymer functionalization to amorphous domains in a semicrystalline polyolefin gel. The beneficial outcomes of blocky functionalization are independent of the identity of the pendant functional group that is installed through functionalization. The decoupling of functional group incorporation and crystallinity highlights the promise in accessing nonrandom microstructures through selective functionalization to circumvent traditional tradeoffs in postpolymerization modification, with potential impact in advanced materials and upcycling plastic waste. 

Blocky bromination of PEKK yields superior crystallizability, high %X_c,T_g,T_m,T_c, and faster crystallization kinetics compared to random analogs. 

Quantitative analysis of particle size and size distribution is crucial in establishing structure–property relationships of composite materials. An emerging soft composite architecture involves dispersing droplets of liquid metal throughout an elastomer, enabling synergistic properties of metals and soft polymers. The structure of these materials is typically characterized through real-space microscopy and image analysis; however, these techniques rely on magnified images that may not represent the global-averaged size and distribution of the droplets. In this study, we utilize ultra-small angle X-ray scattering (USAXS) as a reciprocal-space characterization technique that yields global-averaged dimensions of eutectic gallium indium (EGaIn) alloy soft composites. The Unified fit and Monte Carlo scattering methods are applied to determine the particle size and size distributions of the liquid metal droplets in the composites and are shown to be in excellent agreement with results from real-space image analysis. Additionally, all methods indicate that the droplets are getting larger as they are introduced into composites, suggesting that the droplets are agglomerating or possibly coalescing during dispersion. This work demonstrates the viability of X-ray scattering to elucidate structural information about liquid metal droplets for material development for applications in soft robotics, soft electronics, and multifunctional materials. 

The advancement of triplet–triplet annihilation based upconversion (TTA-UC) in emerging technologies necessitates the development of solid-state systems that are readily accessible and broadly applicable. Here, we demonstrate that thiol–ene click chemistry can be used as a facile cure-on-demand synthetic route to access elastomeric films capable of TTA-UC. Photopolymerization of multifunctional thiols in the presence of a thiol-functionalized 9,10-diphenylanthracene (DPA) emitter results in covalent DPA integration and homogenous crosslinked polymer networks. The palladium( ii ) octaethylporphyrin (PdOEP) sensitizer is subsequently introduced into the films through solution immersion. Upon excitation at 544 nm, green-to-blue upconversion is observed with compositional tuning resulting in an optimal upconverted emission intensity at 1.0 wt% DPA and 0.02 wt% PdOEP. The effectiveness of thiol–ene networks to function as robust host materials for solid-state TTA-UC is further demonstrated by improved photostability in air.