Thermally reprocessable bio-based polymethacrylate vitrimers and nanocomposites

Dynamic Covalent Chemistry of Enamine-Ones: Exploring Tunable Reactivity in Vitrimeric Polymers and Covalent Organic Frameworks

Dynamic covalent chemistry (DCC) has revolutionized the field of polymer science by offering new opportunities for the synthesis, processability, and recyclability of polymers as well as in the development of new materials with interesting properties such as vitrimers and covalent organic frameworks (COFs). Many DCC linkages have been explored for this purpose, but recently, enamine-ones have proven to be promising dynamic linkages because of their facile reversible transamination reactions under thermodynamic control. Their high stability, stimuli-responsive properties, and tunable kinetics make them promising dynamic cross-linkers in network polymers. Given the rapid developments in the field in recent years, this review provides a critical and up-to-date overview of recent developments in enamine-one chemistry, including factors that control their dynamics. The focus of the review will be on the utility of enamine-ones in designing a variety of processable and self-healable polymers with important applications in vitrimers and recyclable closed-loop polymers. The use of enamine-one linkages in crystalline polymers, known as COFs and their applications are also summarized. Finally, we provide an outlook for future developments in this field.

Recyclable and Biobased Vitrimers for Carbon Fibre-Reinforced Composites-A Review

Economic and environmental concerns over the accumulation of end-of-life carbon fibre composite waste have led to increased attention to sustainable materials with low environmental impact. Over decades of research, vitrimers, a modern class of covalent adaptable networks, have bridged the gap between thermoplastics and thermosets. With the distinguishing feature of dynamic covalent bonds, vitrimers can be rearranged and reprocessed within their existing network structures in response to external stimuli such as heat or light. This poses a unique solution to repairing damaged composites, extending their service life, and reducing post-consumer waste. However, the synthesis of vitrimers often requires petrochemical consumption, which increases their carbon footprint. Using bio-based materials could be a promising solution to reduce the reliance on petrochemicals and their related pollution. This review compiles the contemporary requirements for bio-based vitrimers regarding their properties, scalability, and recycling features. This article also presents a comprehensive overview of the pathways to produce sustainable bio-based vitrimers and an overview of promising studies showing the potential uses of bio-derived vitrimers on carbon fibre composite productions.

Closed-Loop Recycling of Vinylogous Urethane Vitrimers

Devising energy-efficient strategies for the depolymerization of plastics and the recovery of their structural components in high yield and purity is key to a circular plastics economy. Here, we report a case study in which we demonstrate that vinylogous urethane (VU) vitrimers synthesized from bis-polyethylene glycol acetoacetates (aPEG) and tris(2-aminoethyl)amine can be degraded by water at moderate temperature with almost quantitative recovery (≈98 %) of aPEG. The rate of depolymerization can be controlled by the temperature, amount of water, molecular weight of aPEG, and composition of the starting material. These last two parameters also allow one to tailor the mechanical properties of the final materials, and this was used to access soft, tough, and brittle vitrimers, respectively. The straightforward preparation and depolymerization of the aPEG-based VU vitrimers are interesting elements for the design of polymer materials with enhanced closed-loop recycling characteristics.

Magnetic Nanoparticles Improve Flow Rate and Enable Self-Healing in Covalent Adaptable Networks

Covalent adaptable networks (CANs) combine the mechanical and chemical stability of thermosets with the reprocessability of thermoplastics through the incorporation of stimuli-responsive dynamic crosslinks. To allow for processing through induction heating, we have created associative CANs that include fillers in the polymer matrix for efficient heat transfer. While the inclusion of inorganic fillers often decreases flow rate in CANs and complicates reprocessing of the material, the presence of Fe₃O₄ nanoparticles had no detrimental effect on flow behavior in a vinylogous urethane vitrimer, an observation we attribute to the catalytic nature of nanoparticles on the dynamic exchange chemistry. We employed two methods of nanoparticle incorporation: blending bare nanoparticles and crosslinking chemically modified nanoparticles. The vitrimers with covalently crosslinked nanoparticles exhibited a decreased relaxation time compared to those with blended nanoparticles. The magnetic character of the Fe₃O₄ nanoparticles enabled self-healing of the vitrimer composite materials upon exposure to an alternating electromagnetic field during induction heating.

Dynamic Ablative Networks: Shapeable Heat-Shielding Materials

Thermoset materials sacrifice recyclability and reshapeability for increased chemical and mechanical robustness because of an immobilized, cross-linked polymeric matrix. The robust material properties of thermosets make them well-suited for applications such as heat-shielding materials (HSMs) or ablatives where excellent thermal stability, good mechanical strength, and high charring ability are paramount. Many of these material properties are characteristic of covalent adaptable networks (CANs), where the static connectivity of thermosets has been replaced with dynamic cross-links. This dynamic connectivity allows network mobility while retaining cross-link connectivity to permit damage repair and reshaping that are traditionally inaccessible for thermoset materials. Herein, we report the synthesis of hybrid inorganic-organic enaminone vitrimers that contain an exceptionally high weight percent of polyhedral oligomeric silsesquioxane (POSS)-derivatives. Polycondensation of β-ketoester-containing POSS with various diamine cross-linkers led to materials with facile tunability, shapeability, predictable glass transition temperatures, good thermal stability, and high residual char mass following thermal degradation. Furthermore, the char materials show notable retention of their preordained shape following decomposition, suggesting their future utility in the design of HSMs with complex detailing.

Self-healable fiber-reinforced vitrimer composites: overview and future prospects

To achieve sustainable development goals, approaches towards the preparation of recyclable and healable polymeric materials is highly attractive. Self-healing polymers and thermosets based on bond-exchangeable dynamic covalent bonds, so called "vitrimers" could be a great effort in this direction. In order to match the industrial importance, enhancement of mechanical strength without sacrificing the bond exchange capability is a challenging issue, however, such concerns can be overcome through the developments of fiber-reinforced vitrimer composites. This article covers the outstanding features of fiber-reinforced vitrimer composites, including their reprocessing, recycling and self-healing properties, together with practical applications and future perspectives of this unique class of materials.

Exploring New Horizons for Bio-Based Poly(furfuryl alcohol) by Exploiting Functionalities Offered by Side Reactions

Poly(furfuryl alcohol) is a bio-based thermoset resin with a limited application portfolio due to its brittleness. Side ring-opening reactions that occur during polymerization lead to carbonyl moieties. Such unique self-generated functionality was exploited to generate tough and ductile materials via the creation of Schiff-based macromolecular architectures.

Combining vinylogous urethane and β-amino ester chemistry for dynamic material design

This study combines vinylogous urethane (VU) and beta-amino ester chemistry for the synthesis of covalent adaptable networks (CANs). The resulting CANs are synthesised using a range of diacetoacetates and commercially...

Epoxidized Block and Statistical Copolymers Reinforced by Organophosphorus-Titanium-Silicon Hybrid Nanoparticles: Morphology and Thermal and Mechanical Properties

Glycidyl methacrylate (GMA) and a mixture of alkyl methacrylates (average chain length of 13 carbons; termed C13MA; derived from vegetable oils) were copolymerized by nitroxide-mediated polymerization to form epoxidized statistical and block copolymers with similar compositions (F GMA ∼0.8), which were further cross-linked by a bio-based diamine. Hybrid plate-like nanoparticles containing organophosphorus-titanium-silicon (PTS) with an average size of ∼130 nm and high decomposition temperature (485 °C) were synthesized via a hydrothermal reaction to serve as additives to simultaneously enhance the thermal and mechanical properties of the blend. Nanocomposites filled with PTS were prepared at different filler-loading levels (0.5, 2, 4 wt %). Transmission electron microscopy (TEM) of the cured block copolymer displayed reaction-induced macrophase-separated domains. TEM also showed an effective dispersion of PTS hybrids in the matrix without intense agglomeration. Thermogravimetric analysis at different heating rates revealed the activation energy of poly (GMA-stat-C13MA) at maximum decomposition increased from 143.5 to 327.2 kJ mol-1 with 4 wt % PTS. Decomposition temperature and char residue improved 12 °C and ∼7 wt %, respectively, and T g increased 12 °C by adding 4 wt % PTS. Targeting various PTS concentrations enabled tuning of the tensile modulus (up to 75%), tensile strength (up to 46%), and storage modulus in both glassy state (up to 59%) and rubbery plateau regions (up to 88%). Oscillatory frequency sweeps indicated that PTS makes the storage modulus frequency dependent, suggesting that the inclusion of the nanoparticles alters the relaxation of the surrounding matrix polymer.

Improving the Physical-Mechanical Property of Dental Composites by Grafting Methacrylate-Polyhedral Oligomeric Silsesquioxane onto a Filler Surface

Endowing dental composites with excellent interfacial bonding through filler surface modification is pivotal to improve the physical-mechanical property and prolong the life of composite fillings. In this study, methacrylate-polyhedral oligomeric silsesquioxane (MA-POSS) acts as a "molecular bridge" between the commonly used SiO₂ particles and the methacrylate-based resin matrix via a thiol-ene click reaction to construct MA-POSS/SiO₂ (p-SiO₂) hybrid particles. Synthesized p-SiO₂ exhibited the roughest surface morphology and had more polymerizable groups, in comparison with SiO₂ and silanized SiO₂. Furthermore, the p-SiO₂ particles were used as a reinforcement to fabricate bisphenol A glycerolate dimethacrylate/tri(ethyleneglycol) dimethacrylate-based dental composites, where the SiO₂- and silanized SiO₂-filled composites served as the control groups, and the filler loading was fixed at 65 wt %. Results of the mechanical properties indicated that the hybrid p-SiO₂ particles significantly improved the flexural strength, flexural modulus, compressive strength, and work of fracture of dental composites, giving improvements of 251.2, 17.89, 122.3, and 1094%, respectively, over the SiO₂-filled composites due to the strong interfacial interaction between the resin matrix and p-SiO₂. Additionally, this optimal p-SiO₂-loaded composite also presented better polymerization shrinkage, acceptable degree of conversion, curing depth, and cell viability. Grafting of MA-POSS onto a filler surface is a promising filler surface modification to improve the resin matrix/filler interfacial interaction, leading to the enhanced overall performance of composites.