Rapid solid-state photopolymerization of octadecyl acrylate: low shrinkage and insensitivity to oxygen

Volumetric Additive Manufacturing of Dicyclopentadiene by Solid-State Photopolymerization

Polymerization in the solid state is generally infeasible due to restrictions on mobility. However, in this work, the solid-state photopolymerization of crystalline dicyclopentadiene is demonstrated via photoinitiated ring-opening metathesis polymerization. The source of mobility in the solid state is attributed to the plastic crystal nature of dicyclopentadiene, which yields local short-range mobility due to orientational degrees of freedom. Polymerization in the solid state enables photopatterning, volumetric additive manufacturing of free-standing structures, and fabrication with embedded components. Solid-state photopolymerization of dicyclopentadiene offers a new paradigm for advanced and freeform fabrication of high-performance thermosets.

Healing Strategy Based on Space Adjustment for Cross-Linked Polymer Networks

Healable materials are notable for their ability to recover from mechanical damage. Most methods for preparing cross-linked healable materials require the introduction of healing agents or supramolecular interactions in solvent environments. Hence, a strategy without the addition of functional component remains a key challenge. Herein, a healing strategy based on space adjustment is proposed with cross-linked poly(octadecyl acrylate) as a model, and this strategy demonstrates that the predesigned holes in cross-linked networks can supply the possibility for polymer coils to move and decrease the space density of the networks during the annealing process. As a result, the motilities of coils are enhanced, which allows them to easily penetrate and entangle in fracture sites. In contrast with the untreated cross-linked poly(octadecyl acrylate), which cannot heal, the space-adjusted poly(octadecyl acrylate) readily heals, and the highest healing efficiency is 96%. The ways in which the extent of space adjustment and the content of the cross-linking agent affect the healing efficiency are discussed, and the mechanism of the space adjustment strategy is studied through rheology research. This strategy concentrates on adjusting the spatial density of the network without the need for any functional design, which may be applied in various polymer systems.

Stiffness Variable Polymers Comprising Phase-Changing Side-Chains: Material Syntheses and Application Explorations

Stiffness variable materials have been applied in a variety of engineering fields that require adaptation, automatic modulation, and morphing because of their unique property to switch between a rigid, load-bearing state and a soft, compliant state. Stiffness variable polymers comprising phase-changing side-chains (s-SVPs) have densely grafted, highly crystallizable long alkyl side-chains in a crosslinked network. Such a bottlebrush network-like structure gives rise to rigidity modulation as a result of the reversible crystallization and melting of the side chains. The corresponding modulus changes can be more than 1000-fold within a narrow temperature span, from ≈10²  MPa to ≈10²  kPa or lower. Other important properties of the s-SVP, such as stretchability, optical transmittance, and adhesion, can also be altered. This work reviews the underlying molecular mechanisms in the s-SVP's, discusses the material's structure-property relationship, and summarizes important applications explored so far, including reversible shape transformation, bistable electromechanical transduction, optical modulation, and reversible adhesion.