Molecular Dynamics Simulation of the Structural, Mechanical, and Reprocessing Properties of Vitrimers Based on a Dynamic Covalent Polymer Network

Abstract

Recyclability and reprocessability of permanently cross-linked polymeric materials have received considerable scientific and technological attention in view of the environmental pollution and sustainable development. By introducing dynamic covalent bonds, vitrimers are emerging as a promising attempt to address this pressing challenge. However, there is still a lack of thermodynamic and kinetic understanding of the bond exchange reactions (BERs) of vitrimers at the molecular level. Herein, by employing coarse-grained molecular dynamics simulations, we successfully construct a model vitrimer system composed of a polymer network formed from linear chains, which can rearrange the network topology via BERs. In this study, we examine the effect of the bond swap energy barrier (ΔE sw ) on a variety of mechanical properties. We find that ΔE sw critically controls the dynamics of the linear chains and the reactive beads located on the linear chain. Our results indicate that the best mechanical performance characteristics are achieved at an intermediate value of ΔE sw . Meanwhile, stress relaxations are examined for different ΔE sw systems. By performing a triaxial deformation to induce the cavities, the vitrimer exhibits excellent self-healing capability by decreasing ΔE sw , as well as increasing the self-healing time and temperature. Lastly, extrusion of polymer vitrimer is simulated, and we find that the extrusion rate tends to increase linearly as ΔE sw decreases. In general, our results provide rational guidelines for designing high-performance vitrimers with good mechanical properties, excellent self-healing ability, and good reprocessability.

Computational study of the transamination reaction in vinylogous acyls: Paving the way to design vitrimers with controlled exchange kinetics

“…Theoretical studies concerning vitrimers reported in the literature are mainly focused in coarse-grained molecular dynamics simulations, which have been used to study and predict the effect of different parameters, such as the bond swap energy barrier and exchange rate, on the macroscopic properties of these materials. [48][49][50] However, computational studies at the atomic level using density functional theory to study the kinetics of the exchange reaction are scarce. 51 In this work, we aim to use density functional theory (DFT) calculations to render detailed information about exchange kinetics at the level of electrons, that is, the manifestation of electronic structures on the monomer scale, in the pursuit of promising candidates to develop new vitrimeric materials.…”

“…Since a large number of chemical modifications may arise, the development of new vitrimers can be accelerated by intensive use of computational chemistry to guide the design of the most promising structures, as opposed to the common trial‐and‐error procedure guided by chemical intuition. Theoretical studies concerning vitrimers reported in the literature are mainly focused in coarse‐grained molecular dynamics simulations, which have been used to study and predict the effect of different parameters, such as the bond swap energy barrier and exchange rate, on the macroscopic properties of these materials 48–50 . However, computational studies at the atomic level using density functional theory to study the kinetics of the exchange reaction are scarce 51 …”

Associative bond swaps in molecular dynamics

“…[19]. This recipe to model swaps has already been able to provide meaningful results in the context of smart vitrimers [20][21][22][23][24], or in the assembly of soft particles [25][26][27].…”

Hardener Isomerism and Content of Dynamic Disulfide Bond Effect on Chemical Recycling of Epoxy Networks

“…At present, those kind of systems are still at a research level due to their complex chemistry, expensiveness, long-term stability issues, and nonenvironmental friendliness, among others. , One of the most promising technologies is to introduce dynamic covalent bonds within the polymeric structure that are able to respond to external stimuli, thus creating covalent adaptable networks. , There are already several existing approaches, based on different technologies, such as transesterification, , Diels–Alder adduct chemistry, imine bonds, disulfide bonds, dynamic B–O bonds, hemiaminals/hexahydrotriazines, and acetal linkages, among others.…”

“…2,6 One of the most promising technologies is to introduce dynamic covalent bonds within the polymeric structure that are able to respond to external stimuli, thus creating covalent adaptable networks. 7,8 There are already several existing approaches, based on different technologies, such as transesterification, 9,10 Diels−Alder adduct chemistry, 11 imine bonds, 12 disulfide bonds, 13 dynamic B−O bonds, 14 hemiaminals/hexahydrotriazines, 15 and acetal linkages, 16 among others. More specifically, disulfide linkages have been widely used for this purpose since 1990 when Tesoro and Sastri introduced them for the first time into epoxy networks.…”