Recent progress on stretchable, tough dual-dynamic polymer single networks (SN) and interpenetrated networks (IPN) has broadened the potential applications of dynamic polymers. However, the impact of macromolecular structure on the material mechanics remains poorly understood. Here, rapidly exchanging hydrogen bonds and thermoresponsive Diels–Alder bonds were included into molecularly engineered interpenetrated network materials. RAFT polymerization was used to make well-defined polymers with control over macromolecular architecture. The IPN materials were assessed by gel permeation chromatography, differential scanning calorimetry, tensile testing and rheology. The mechanical properties of these IPN materials can be tuned by varying the crosslinker content and chain length. All materials are elastic and have dynamic behavior at both ambient temperature and elevated temperature (90 °C), owing to the presence of the dual dynamic noncovalent and covalent bonds. 100% self-healing recovery was achieved and a maximum stress level of up to 6 MPa was obtained. The data suggested the material's healing properties are inversely proportional to the content of the crosslinker or the degree of polymerization at both room and elevated temperature. The thermoresponsive crosslinker restricted deformation to some extent in an ambient environment but gave excellent malleability upon heating. The underlying mechanism was explored by the computational simulations. Furthermore, a single network material with the same crosslinker content and degree of polymerization as the IPN was made. The SN was substantially weaker than the comparable IPN material.
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Controlling polymer architecture to design dynamic network materials with multiple dynamic linkers
A one pot synthesis is applied to control the chain structure and architecture of multiply dynamic polymers, enabling fine tuning of materials properties by choice of polymer chain length or crosslink density. Macromolecules containing both non-covalent linkers based on quadruple hydrogen-bonded 2-(((6-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)hexyl)carbamoyl)oxy)ethyl methacrylate (UPyMA), and thermoresponsive dynamic covalent furan–maleimide based Diels–Alder linkers are explored. The primary polymer's architecture was controlled by reversible addition-fragmentation chain transfer (RAFT) polymerization, with the dynamic non-covalent (UPyMA) and dynamic covalent furfuryl methacrylate (FMA) units incorporated into the same backbone. The materials are crosslinked, taking advantage of the “click” chemistry properties of the furan–maleimide reaction. The polymer materials showed stimulus-responsive thermomechanical properties with a decrosslinking temperature increasing with the polymer's primary chain length and crosslink density. The polymers had good thermally promoted self-healing properties due to the dynamic covalent Diels–Alder bonds. Besides, the materials had excellent stress relaxation characteristics induced by the exchange of the hydrogen bonds in UPyMA units.
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- Award ID(s):
- 1749730
- NSF-PAR ID:
- 10218010
- Date Published:
- Journal Name:
- Molecular Systems Design & Engineering
- Volume:
- 5
- Issue:
- 7
- ISSN:
- 2058-9689
- Page Range / eLocation ID:
- 1267 to 1276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The inability to re‐process thermosets hinders their utility and sustainability. An ideal material should combine closed‐loop recycling and upcycling capabilities. This trait is realized in polydimethylsiloxane bottlebrush networks using thermoreversible Diels–Alder cycloadditions to enable both reversible disassembly into a polymer melt and on‐demand reconfiguration to an elastomer of either lower or higher stiffness. The crosslink density was tuned by loading the functionalized networks with a controlled fraction of dormant crosslinkers and crosslinker scavengers, such as furan‐capped bis‐maleimide and anthracene, respectively. The resulting modulus variations precisely followed the stoichiometry of activated furan and maleimide moieties, demonstrating the lack of side reactions during reprocessing. The presented circularity concept is independent from the backbone or side chain chemistry, making it potentially applicable to a wide range of brush‐like polymers.
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Abstract Dynamic bonds introduce unique properties such as self‐healing, recyclability, shape memory, and malleability to polymers. Significant efforts have been made to synthesize a variety of dynamic linkers, creating a diverse library of materials. In addition to the development of new dynamic chemistries, fine‐tuning of dynamic bonds has emerged as a technique to modulate dynamic properties. This Review highlights approaches for controlling the timescales of dynamic bonds in polymers. Particularly, eight dynamic bonds are considered, including urea/urethanes, boronic esters, Thiol–Michael exchange, Diels–Alder adducts, transesterification, imine bonds, coordination bonds, and hydrogen bonding. This Review emphasizes how structural modifications and external factors have been used as tools to tune the dynamic character of materials. Finally, this Review proposes strategies for tailoring the timescales of dynamic bonds in polymer materials through both kinetic effects and modulating bond thermodynamics.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0ME00015A
