Dynamics and reaction kinetics of coarse-grained bulk vitrimers: a molecular dynamics study

Wu, Jianbo; Li, Shu-Jia; Li, Hong; Huang, Qian; Lu, Zhong‐Yuan

doi:10.1039/c9cp01766f

Cited by 49 publications

(71 citation statements)

References 56 publications

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“… 34 For CANs above T g , where flow is limited by the bond exchange, the primary contribution to E a is the activation energy required for the bond exchange reaction. 35 However, the activation energy of viscous flow may be affected by many properties of the network, including polymer identity, topology, and cross-link density. 31 As such, CANs with identical exchange chemistries may demonstrate varied values of E a .…”

Section: Characteristics Of Vitrimersmentioning

confidence: 99%

Reprocessable Cross-Linked Polymer Networks: Are Associative Exchange Mechanisms Desirable?

2020

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Covalent adaptable networks (CANs) are covalently cross-linked polymers that may be reshaped via cross-linking and/or strand exchange at elevated temperatures. They represent an exciting and rapidly developing frontier in polymer science for their potential as stimuli-responsive materials and to make traditionally nonrecyclable thermosets more sustainable. CANs whose cross-links undergo exchange via associative intermediates rather than dissociating to separate reactive groups are termed vitrimers. Vitrimers were postulated to be an attractive subset of CANs, because associative cross-link exchange mechanisms maintain the original cross-link density of the network throughout the exchange process. As a result, associative CANs demonstrate a gradual, Arrhenius-like reduction in viscosity at elevated temperatures while maintaining mechanical integrity. In contrast, CANs reprocessed by dissociation and reformation of cross-links have been postulated to exhibit a more rapid decrease in viscosity with increasing temperature. Here, we survey the stress relaxation behavior of all dissociative CANs for which variable temperature stress relaxation or viscosity data are reported to date. All exhibit an Arrhenius relationship between temperature and viscosity, as only a small percentage of the cross-links are broken instantaneously under typical reprocessing conditions. As such, dissociative and associative CANs show nearly identical reprocessing behavior over broad temperature ranges typically used for reprocessing. Given that the term vitrimer was coined to highlight an Arrhenius relationship between viscosity and temperature, in analogy to vitreous glasses, we discourage its continued use to describe associative CANs. The realization that the cross-link exchange mechanism does not greatly influence the practical reprocessing behavior of most CANs suggests that exchange chemistries can be considered with fewer constraints, focusing instead on their activation parameters, synthetic convenience, and application-specific considerations.

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Section: Characteristics Of Vitrimersmentioning

confidence: 99%

Reprocessable Cross-Linked Polymer Networks: Are Associative Exchange Mechanisms Desirable?

2020

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“…In addition, to solve the problem of the depletion of petroleum resources, the use of bio-based monomers for the preparation of vitrimers has gained attention [ 98 , 99 , 100 ]. For the practical application of the vitrimer concept, the molecular-level control of the basic physics and flow properties of vitrimers, e.g., stress–relaxation and linear viscoelasticity, have also been studied, because these properties are closely related to material processing [ 101 , 102 , 103 , 104 , 105 , 106 , 107 ]. Because vitrimers are still relatively new, further development of vitrimers, including the design, the modification of properties, functionalization, and the discovery of new application ranges (such as for shape memory polymers [ 65 , 80 , 98 , 103 , 108 , 109 , 110 , 111 , 112 , 113 ] and 3D printer resin [ 114 , 115 ]), is highly favorable and can surely lead to the realization of a sustainable society.…”

Section: Discussionmentioning

confidence: 99%

Implantation of Recyclability and Healability into Cross-Linked Commercial Polymers by Applying the Vitrimer Concept

Hayashi

2020

Polymers

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Vitrimers are a new class of cross-linked materials that are capable of network topology alternation through the associative dynamic bond-exchange mechanism, which has recently been invented to solve the problem of conventional cross-linked materials, such as poor recyclability and healability. Thus far, the concept of vitrimers has been applied to various commercial polymers, e.g., polyesters, polylactides, polycarbonates, polydimethylsiloxanes, polydienes, polyurethanes, polyolefins, poly(meth)acrylates, and polystyrenes, by utilizing different compatible bond-exchange reactions. In this review article, the concept of vitrimers is described by clarifying the difference from thermoplastics and supramolecular systems; in addition, the term “associative bond-exchange” in vitrimers is explained by comparison with the “dissociative” term. Several useful functions attained by the vitrimer concept (including recyclability and healability) are demonstrated, and recent molecular designs of vitrimers are classified into groups depending on the types of molecular frameworks. This review specifically focuses on the vitrimer molecular designs with commercial polymer-based frameworks, which provide useful hints for the practical application of the vitrimer concept.

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“…Such a simulation scheme can also be used to study the interfacial self-healing behaviors of dynamic polymer networks (Stukalin et al, 2013). For e.g., coarse-grained MD models have been recently developed to study the change of polymer networks under the influence of reversible bonds (Amin et al, 2016;Wu et al, 2019). The reversible bonds can be formed due to the dynamic covalent bonds, hydrogen bonds, metal-ligand coordination, and ionic interactions.…”

Section: Simulations Of Covalent Adaptable Polymer Networkmentioning

confidence: 99%

Smart Polymers for Advanced Applications: A Mechanical Perspective Review

2020

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Responsive materials, as well as active structural systems, are today widely used to develop unprecedented smart devices, sensors, or actuators; their functionalities come from the ability to respond to environmental stimuli with a detectable reaction. Depending on the responsive material under study, the triggering stimuli can have a different nature, ranging from physical (temperature, light, electric or magnetic field, mechanical stress, etc.), chemical (pH, ligands, etc.), or biological (enzymes, etc.) type. Such a responsiveness can be obtained by properly designing the meso-or macroscopic arrangement of the constitutive elements, as occurs in metamaterials, or can be obtained by using responsive materials per se, whose responsiveness comes from the chemistry underlying their microstructure. In fact, when the responsiveness at the molecular level is properly organized, the nanoscale response can be collectively detected at the macroscale, leading to a responsive material. In the present article, we review the enormous world of responsive polymers, by outlining the main features, characteristics, and responsive mechanisms of smart polymers and by providing a mechanical modeling perspective, both at the molecular as well as at the continuum scale level. We aim at providing a comprehensive overview of the main features and modeling aspects of the most diffused smart polymers. The quantitative mechanical description of active materials plays a key role in their development and use, enabling the design of advanced devices as well as to engineer the materials' microstructure according to the desired functionality.

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Dynamics and reaction kinetics of coarse-grained bulk vitrimers: a molecular dynamics study

Abstract: We used the hybrid molecular dynamics–Monte Carlo (MD–MC) algorithm to establish a molecular dynamics model that can accurately reflect bond exchange reactions, and reveal the intrinsic mechanism of the dynamic behavior of the vitrimer system.

Cited by 49 publications

References 56 publications

Reprocessable Cross-Linked Polymer Networks: Are Associative Exchange Mechanisms Desirable?

Reprocessable Cross-Linked Polymer Networks: Are Associative Exchange Mechanisms Desirable?

Implantation of Recyclability and Healability into Cross-Linked Commercial Polymers by Applying the Vitrimer Concept

Smart Polymers for Advanced Applications: A Mechanical Perspective Review

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