Vitrimer Chemistry and Applications

Abstract

Vitrimers are permanent yet dynamic polymer networks that ideally behave like conventional thermosets at service temperatures but flow like vitreous glasses at processing temperatures. They are characterized by constant, temperature‐independent network connectivity as well as the ability to completely relax stress as a result of dynamic exchange reactions between the cross‐links. Other important features include enhanced insolubility, healing properties, and facile shaping. Since the introduction of vitrimers in 2011, which were epoxy‐acid and epoxy‐anhydride resins loaded with a transesterification catalyst, many kinds of dynamic covalent chemistries have been employed in polymer networks to create new vitrimers. Born from these advancements, exciting new applications have been reported that cannot be realized with conventional thermosets. In this article, we introduce fundamental principles of vitrimer science and provide an overview of recent advances in vitrimer chemistry. Finally, we discuss the use of vitrimers in recycling, shape‐memory materials, composites, and a variety of other nascent applications.

Fragile Glass Formation and Non-Arrhenius Upturns in Ethylene Vitrimers Revealed by Dielectric Spectroscopy

“…Vitrimers are a subcategory of dynamic covalent networks where the polymeric backbones are cross-linked by associative exchangeable bonds. − Unlike supramolecular polymers and dissociative dynamic covalent networks that undergo breaking and reforming reactions of physical bonds, vitrimers undergo exchange reactions that do not involve bond breaking. These materials have received fast-growing interest from the recyclable polymer research community due to their unique self-healing properties, easy reprocessability, and recyclability, and the numerous dynamic covalent chemistries that can be used to tailor these properties. − While a large body of work has been directed toward investigating the self-healing, recyclability, and stress relaxation behavior of these networks, focus in recent years has shifted toward investigating the effect of bond exchange on properties other than those investigated using rheology and self-healing measurements, such as crystallization, phase separation, and self-assembly. , Vitrimers are also being investigated as functional materials with applications in solid polymer electrolytes, super-hydrophobic coatings, shape-memory materials, , and adhesives . For these areas, a more comprehensive understanding of dynamics across length scales is required for materials design and optimization.…”

Regiospecific Synthesis of a Reprocessable Galactan-Mimic via Topochemical Polymerization

“…Covalent adaptable network (CAN) polymers made by cross-linking 1D polymers via linkers that form dynamic covalent linkages are of interest in view of their reprocessability, stimuli-responsive reversibility, high stability, strength, etc. − They find applications in soft robotics, tissue engineering, smart materials, etc. − Boronic acids are known to react reversibly with vicinal diols to form boronate esters, and the reversible nature of this reaction makes diboronic acids ideal cross-linkers for synthesizing CANs (Figure a). − There is great interest in boronic acid-cross-linked CANs made from natural polysaccharides in view of their enhanced properties. − Natural polysaccharides can have a maximum of one vicinal diol unit per repeating unit and hence can make only one boronate linkage per repeating unit. On the other hand, 1D polymers made from inositols can have up to two vicinal diol units per repeating unit that allow two boronate linkages per repeating unit (Figure b).…”

Discovery of Kinetic Trapping of Poloxamers inside Liposomes via Thermal Treatment

“…Poloxamers are nonionic ABPs with PEO–PPO–PEO triblock architecture that are commercially available over a range of molecular weights and compositions and are biocompatible. , Poloxamer binding to phospholipid bilayers is endothermic, driven by entropically dominated hydrophobic forces. , Because the hydrophobic effect and the hydrogen-bonded water shell of PEO and PPO are sensitive to temperature, it is important to understand how temperature and thermal history affect poloxamer–lipid bilayer interactions. However, most mechanistic studies of polymer–lipid bilayer interactions have been conducted at a single temperature, often room temperature, for experimental convenience or because the effects of other variables were the focus. ,,,,− …”

“…A fundamental understanding of interactions between amphiphilic block copolymers (ABPs) and phospholipids is important for a range of fields including cosmetics, food, nanoreactors, and drug delivery. − Due to the amphiphilic nature of both ABPs and phospholipids, ABPs can self-assemble with phospholipids to make hybrid polymer–lipid bilayers − or can bind to vesicle surfaces after fabrication. − In both cases, ABPs have a profound impact on the structure and dynamics of lipid packing, ,,− manipulate mechanical properties such as the bending and stretching moduli, − ,, and can alter the vesicle morphology . Therefore, ABPs can be used to tailor the mechanical and surface properties of lipids and polymer–lipid vesicles for specific applications.…”