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1. Efficient Manufacture, Deconstruction, and Upcycling of High-Performance Thermosets and Composites

   https://doi.org/10.1021/acsaenm.2c00115  

   Lloyd, Evan M.; Cooper, Julian C.; Shieh, Peyton; Ivanoff, Douglas G.; Parikh, Nil A.; Mejia, Edgar B.; Husted, Keith E.; Costa, Letícia C.; Sottos, Nancy R.; Johnson, Jeremiah A.; et al (November 2022, ACS Applied Engineering Materials)

   Thermoset polymers and fiber-reinforced polymer composites possess the chemical, physical, and mechanical properties necessary for energy-efficient vehicles and structures, but their energy-inefficient manufacturing and the lack of end-of-life management strategies render these materials unsustainable. Here, we demonstrate end-of-life deconstruction and upcycling of high-performance poly(dicyclopentadiene) (pDCPD) thermosets with a concurrent reduction in the energy demand for curing via frontal copolymerization. Triggered material deconstruction is achieved through cleavage of cyclic silyl ethers and acetals incorporated into pDCPD thermosets. Both solution-state and bulk experiments reveal that seven- and eight-membered cyclic silyl ethers and eight-membered cyclic acetals are incorporated efficiently with norbornene-derived monomers, permitting deconstruction at low comonomer loadings. Frontal copolymerization of DCPD with these tailored cleavable comonomers enables energy-efficient manufacturing of sustainable, high-performance thermosets with glass transition temperatures of >100 °C and elastic moduli of >1 GPa. The polymers are fully deconstructed, yielding hydroxyl-terminated oligomers that are upcycled to polyurethane-containing thermosets having a higher glass transition temperatures than that of the original polymer upon reaction with diisocyanates. This approach is extended to frontally polymerized fiber-reinforced composites, where large-fiber volume fraction composites (Vf = 65%) containing a cleavable comonomer are deconstructed and the reclaimed fibers are used to regenerate composites via frontal polymerization that display properties nearly identical to those of the original. This work demonstrates that the use of cleavable monomers, in combination with frontal manufacturing, provides a promising strategy to address sustainability challenges for high-performance materials at multiple stages of their lifecycle. 

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2. Toughening and Imparting Deconstructability to 3D‐Printed Glassy Thermosets with “Transferinker” Additives

   https://doi.org/10.1002/adma.202406600  

   Qin, K_Peter; Herzog‐Arbeitman, Abraham; Zou, Weizhong; Chakraborty, Saswata; Kristufek, Samantha_L; Husted, Keith_E_L; Joly, Guy_D; Craig, Stephen_L; Olsen, Bradley_D; Johnson, Jeremiah_A (September 2024, Advanced Materials)

   Abstract Thermoset toughness and deconstructability are often opposing features; simultaneously improving both without sacrificing other mechanical properties (e.g., stiffness and tensile strength) is difficult, but, if achieved, could enhance the usage lifetime and end‐of‐life options for these materials. Here, a strategy that addresses this challenge in the context of photopolymer resins commonly used for 3D printing of glassy, acrylic thermosets is introduced. It is shown that incorporating bis‐acrylate “transferinkers,” which are cross‐linkers capable of undergoing degenerative chain transfer and new strand growth, as additives (5–25 mol%) into homemade or commercially available photopolymer resins leads to photopolymer thermosets with substantially improved tensile toughness and triggered chemical deconstructability with minimal impacts on Young's moduli, tensile strengths, and glass transition temperatures. These properties result from a transferinker‐driven topological transition in network structure from the densely cross‐linked long, heterogeneous primary strands of traditional photopolymer networks to more uniform, star‐like networks with few dangling ends; the latter structure more effectively bear stress yet is also more easily depercolated via solvolysis. Thus, transferinkers represent a simple and effective strategy for improving the mechanical properties of photopolymer thermosets and providing a mechanism for their triggered deconstructability. 

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3. Carbon Foam/CaCl ₂ ·6H ₂ O Composite as a Phase-Change Material for Thermal Energy Storage

   https://doi.org/10.1021/acs.energyfuels.3c01275  

   Jing, Yikang; Dixit, Kunal; Schiffres, Scott N; Liu, Hao (July 2023, Energy & Fuels)

   Inorganic salt hydrates are promising phase-change materials (PCMs) for thermal energy storage due to their high latent heat of fusion. However, their practical application is often limited by their unstable form, dehydration, large supercooling, and low thermal conductivity. Porous melamine foam and its carbonized derivatives are potential supporting porous materials to encapsulate inorganic salt hydrate PCMs to address these problems. This work investigates the effect of pyrolysis temperature on the morphology and structure of the carbonized foams and their thermal energy storage performance. Pyrolysis of melamine foam at 700−900 °C leads to the formation of crystalline sodium cyanate and sodium carbonate particles on the foam skeleton surface, which allows the spontaneous impregnation of the carbon foam with molten CaCl2·6H2O.The form-stable foam-CaCl2·6H2O composite effectively suppresses supercooling and dehydration, demonstrating the efficacy of carbon foam as a promising supporting material for inorganic salt hydrate PCMs. 

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4. Bio-Based Thiol–ene Network Thermosets from Isosorbide and Terpenes

   https://doi.org/10.1021/acsmacrolett.4c00078  

   Prebihalo, Emily A; Johnson, Melody; Reineke, Theresa M (May 2024, ACS Macro Letters)

   Thermoset networks are chemically cross-linked materials that exhibit high heat resistance and mechanical strength; however, the permanently cross-linked system makes end-of-life degradation difficult. Thermosets that are inherently degradable and made from renewably derived starting materials are an underexplored area in sustainable polymer chemistry. Here, we report the synthesis of novel sugar- and terpene-based monomers as the enes in thiol–ene network formation. The resulting networks showed varied mechanical properties depending on the thiol used during cross-linking, ranging from strain-at-breaks of 12 to 200%. Networks with carveol or an isosorbide-based thiol incorporated showed plastic deformation under tensile stress testing, while geraniol-containing networks demonstrated linear stress–strain behavior. The storage modulus at the rubbery plateau was highly dependent on the thiol cross-linker, showing an order of magnitude difference between commercial PETMP, DTT, and synthesized Iso2MC. Thermal degradation temperatures were low for the networks, primarily below 200 °C, and the Tg values ranged from −17 to 31 °C. Networks were rapidly degraded under basic conditions, showing complete degradation after 2 days for nearly all synthesized thermosets. This library demonstrates the range of thermal and mechanical properties that can be targeted using monomers from sugars and terpenes and expands the field of renewably derived and degradable thermoset network materials. 

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5. Facile Catalyst‐Free Approach toward Fully Biobased Reprocessable Lignin Thermosets

   https://doi.org/10.1002/macp.202200303  

   Buzoglu Kurnaz, Leman; Bension, Yishayah; Tang, Chuanbing (October 2022, Macromolecular Chemistry and Physics)

   Abstract Reprocessable and biobased thermosets are prepared from two renewable feedstocks, lignin and polyamine (Priamine 1071). Lignin is oxidized to produce polycarbonyl and further reacts with polyamine to form a crosslinked network of imines. The thermoset materials are formed under heat and pressure in the absence of any catalysts. The mechanical strength and thermal properties of thermosets are tunable by changing feedstock ratios. The dynamic imine crosslinks can be associatively reformed. 

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