High sensitivity capacitive pressure sensors can be created with bottlebrush dielectric layers that overcome the limitations of traditional polymeric materials.
Super-soft elastomers derived from bottlebrush polymers show promise as advanced materials for biomimetic tissue and device applications, but current processing strategies are restricted to simple molding. Here, we introduce a design concept that enables the three-dimensional (3D) printing of super-soft and solvent-free bottlebrush elastomers at room temperature. The key advance is a class of inks comprising statistical bottlebrush polymers that self-assemble into well-ordered body-centered cubic sphere phases. These soft solids undergo sharp and reversible yielding at 20°C in response to shear with a yield stress that can be tuned by manipulating the length scale of microphase separation. The addition of a soluble photocrosslinker allows complete ultraviolet curing after extrusion to form super-soft elastomers with near-perfect recoverable elasticity well beyond the yield strain. These structure–property design rules create exciting opportunities to tailor the performance of 3D-printed elastomers in ways that are not possible with current materials and processes.
We demonstrate a universal approach to form bottlebrush polymer networks in both bulk and thin films by photo-crosslinking mixtures of well-defined bottlebrush precursors and bis-benzophenone-based additives. This strategy is compatible with a wide variety of different side-chain chemistries including poly(acrylates), poly(ethers), poly(esters), and poly(siloxanes) due to the indiscriminate C–H abstraction behavior of benzophenone upon exposure to ultraviolet light. The appropriate choice of molecular “linker” that bridges benzophenones is critical to solubilize the additive in a given bottlebrush precursor at room temperature without a solvent. Importantly, homogeneous mixtures can be achieved using two distinct types of linkers: telechelic polymers matched to the bottlebrush side-chain chemistry or small-molecule branched alkyl derivatives that are often synthetically more accessible. As evidenced by in situ UV shear rheology, the curing kinetics and mechanical properties of these amorphous or semicrystalline networks are controlled by bottlebrush precursor chemistry, architecture, and crosslinker loading. The influence of elastically effective and ineffective crosslinks, which arise in tandem from the statistical nature of benzophenone-induced radical reactions, is quantitatively captured by introducing a general model that relates crosslinker concentration and shear modulus. These results provide a conceptual framework that can be used to conveniently synthesize bottlebrush networks with tailored properties.
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