Self-healing polymers based on thermally reversible Diels–Alder chemistry
Polym. Chem 03/2013; 4(7):2194-2205. DOI: 10.1039/C2PY20957H
The development of self-healing materials has received much research attention in the last two decades. This review paper gathers recent publications on the self-healing polymeric materials with thermally reversible Diels–Alder (DA) chemistry. The DA reaction is a [4 + 2] cycloaddition involving a diene and a dienophile. The self-healing polymers employing the furan group as a diene and the maleimide group as a dienophile have been widely studied. Multifunctional furan and maleimide compounds construct thermally reversible crosslinked networks showing removability and remendability. Self-healing materials have also been utilized as healing agents for conventional thermosets like epoxy resins. Other diene–dienophile pairs, such as anthracene–maleimide and cyclopentadiene–dicyclopentadiene, have also been utilized for the development of thermally induced self-healing materials. Photo-induced self-healing polymers and some novel applications based on DA reactions have been discussed in this review. Moreover, self-healing polymer systems based on other thermally triggered and assisted reactions are also discussed. The discussed publication has provided promising molecular designs and synthetic strategies for the development of high performance self-healing polymers.
Article: Stimuli-responsive polymer films[Show abstract] [Hide abstract]
ABSTRACT: Stimuli-responsive polymer films undergo interesting structural and property changes upon external stimuli. Their applications have extended from smart coatings to controlled drug release, smart windows, self-repair and other fields. This tutorial review summarizes non-covalent bonding, reversible reactions and responsive molecules that have played important roles in creating stimuli-responsive systems, and presents the recent development of three types of responsive polymer systems: layer-by-layer polymer multilayer films, polymer brushes, and self-repairing polymer films, with a discussion of their response mechanism. Future research efforts include comprehensive understanding of the response mechanism, producing polymer systems with controlled response properties regarding single or multiple external signals, combining polymer film fabrication with nanotechnology, improving the stability of polymer films on substrates, and evaluating the toxicity of the degradation products.
Chapter: Diels-Alder Polymers[Show abstract] [Hide abstract]
ABSTRACT: The Diels–Alder (DA) cycloaddition is extensively used in polymer chemistry. Linear, network, and hyperbranched polymers have been prepared from monomers and prepolymers containing a diene and a dienophile. Because of the simple reaction conditions, high yield, and high selectivity, the DA reaction has recently been rerecognized as a member of the click-chemistry family. Polymers with unique architectures (e.g., block and graft copolymers, star polymers, telechelic polymers, dendrimers, and dendronized polymers) have been prepared based on this concept. Many DA reactions are thermally reversible. Enthalpically favorable forward cycloaddition reaction proceeds at low temperature, whereas the opposite cycloreversion proceeds at moderate-to-high temperature. Among the various options for optimizing DA reactions in polymer synthesis, researchers have focused on the diene–dienophile combination. Ease of reactant preparation, reaction rate of the DA cycloaddition, equilibrium constant of the DA reaction at room temperature, and temperature above which the retro-DA reaction proceeds are key points in choosing this option. In addition, reversibility has been exploited in developing various functional polymers such as recyclable gels and thermosets, shape-memory polymers, and crack-healing polymers. This article surveys DA reactions in polymer synthesis and coupling, including the click-chemistry approach, and functionality of DA polymers mainly based on the reversibility.Keywords:Diels–Alder reaction;click chemistry;reversible polymerization/cross-linking;healing polymer
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ABSTRACT: Bio-inspired molecular design and synthesis of high-performance and recyclable cross-linked polymers is reported. Reversible cross-links between hard segments are incorporated into linear segmented polyurethane via Diels-Alder reaction between maleimide pendant group and furan cross-linker. The materials form hierarchical structure and exhibit excellent properties with high stiffness, strength and toughness, and can be easily thermally reshaped and re-mended.
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