Effect of bond exchange rate on dynamics and mechanics of vitrimers
About: This article is published in Journal of Polymer Science.The article was published on 2021-08-05. It has received 13 citations till now.
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TL;DR: In this article , the role of dynamic covalent chemistry on self-assembly is highlighted in the context of crystallization and nanophase separation, as well as the ability of dynamic bond exchange to manipulate molecular transport and viscoelasticity.
Abstract: Vitrimers have been investigated in the past decade for their promise as recyclable, reprocessable, and self-healing materials. In this Viewpoint, we focus on some of the key open questions that remain regarding how the molecular-scale chemistry impacts macroscopic physical chemistry. The ability to design temperature-dependent complex viscoelastic spectra with independent control of viscosity and modulus based on knowledge of the dynamic bond and polymer chemistry is first discussed. Next, the role of dynamic covalent chemistry on self-assembly is highlighted in the context of crystallization and nanophase separation. Finally, the ability of dynamic bond exchange to manipulate molecular transport and viscoelasticity is discussed in the context of various applications. Future directions leveraging dynamic covalent chemistry to provide insights regarding fundamental polymer physics as well as imparting functionality into polymers are discussed in all three of these highlighted areas.
24 citations
TL;DR: In this article , the authors analyze structure-reactivity-property relationships for several classes of CANs, illustrating both general design principles and the predictive potential of linear free energy relationships (LFERs) applied to CANs.
Abstract: Polymer networks built out of dynamic covalent bonds offer the potential to translate the control and tunability of chemical reactions to macroscopic physical properties. Under conditions at which these reactions occur, the topology of covalent adaptable networks (CANs) can rearrange, meaning that they can flow, self-heal, be remolded, and respond to stimuli. Materials with these properties are necessary to fields ranging from sustainability to tissue engineering; thus the conditions and time scale of network rearrangement must be compatible with the intended use. The mechanical properties of CANs are based on the thermodynamics and kinetics of their constituent bonds. Therefore, strategies are needed that connect the molecular and macroscopic worlds. In this Perspective, we analyze structure-reactivity-property relationships for several classes of CANs, illustrating both general design principles and the predictive potential of linear free energy relationships (LFERs) applied to CANs. We discuss opportunities in the field to develop quantitative structure-reactivity-property relationships and open challenges.
13 citations
TL;DR: In this article , the effect of branch numbers at the cross-link point of a transesterification-based vitrimer network on its bond exchange properties was investigated, where f can be readily tuned via the functionality of the starting materials.
Abstract: Vitrimers are functional cross-linked materials, exhibiting reprocessability, recyclability, and healability, and thus these are expected for application as sustainable materials. The functionalities of vitrimers are attributable to their associative bond exchange mechanism that is activated at a certain high temperature. The construction of a tuning method for the bond exchange properties must be useful for coming practical application of the vitrimer concept. Here, we prepare transesterification-based vitrimers via the thiol–epoxy click reaction to elucidate the essential effects of the branch numbers (f) at the cross-link point on their bond exchange properties, where f can be readily tuned via the functionality of the starting materials. The temperature-ramp creep and stress–relaxation tests then demonstrate that the vitrimer properties, such as the softening and stress–relaxation behaviors, vary depending on f. The experimental results derive some empirical relationships between f and the relaxation time and between f and activation energy of the bond exchange. In addition, the relaxation behavior of the vitrimer network with mixed f is investigated in the final section, showing the relaxation rate can be determined by the harmonic mean of relaxation time weighted by the mole fraction of the network components having different f. Overall, this study demonstrates that the design of a proper f is crucial to obtain the desired properties of vitrimers.
9 citations
TL;DR: In this article , the state-of-the-art in the utilization of boronic species for the synthesis of covalent adaptable networks is provided, where the authors mainly focus on the synthetic aspects of BORonic linkages-based vitrimers construction.
Abstract: Growing environmental awareness imposes on polymer scientists the development of novel materials that show a longer lifetime and that can be easily recycled. These challenges were largely met by vitrimers, a new class of polymers that merges properties of thermoplastics and thermosets. This is achieved by the incorporation of dynamic covalent bonds into the polymer structure, which provides high stability at the service temperature, but enables the processing at elevated temperatures. Numerous types of dynamic covalent bonds have been utilized for the synthesis of vitrimers. Amongst them, boronic acid-based linkages, namely boronic acid esters and boroxines, are distinguished by their quick exchange kinetics and the possibility of easy application in various polymer systems, from commercial thermoplastics to low molecular weight thermosetting resins. This review covers the development of dynamic cross-links. This review is aimed at providing the state of the art in the utilization of boronic species for the synthesis of covalent adaptable networks. We mainly focus on the synthetic aspects of boronic linkages-based vitrimers construction. Finally, the challenges and future perspectives are provided.
8 citations
TL;DR: In this paper , a hybrid molecular dynamics/Monte Carlo simulation is used to study the microscopic dynamics and the macroscopic rheology of vitrimers with a fast bond exchange rate.
Abstract: We implement a hybrid molecular dynamics/Monte Carlo simulation to study the microscopic dynamics and the macroscopic rheology of vitrimers with a fast bond exchange rate. We show that the linear viscoelastic properties and mean squared displacement of the vitrimers collapse onto master curves by applying the same shift factors that follow the Williams–Landel–Ferry equation at low temperatures and Arrhenius-like behavior at high temperatures. The linkage between the microscopic dynamics and the linear rheology of vitrimers is established using the generalized Stokes–Einstein relationship, which efficiently extends the timescale of simulations and predicts the viscoelasticity. The values of the shift factors are related to the characteristic decay time of the intermediate scattering function, which is accessible in scattering experiments. The same results hold in the case of an all-atom model of an ionic liquid. Our methodology provides a microscopic basis for the time-superposition principle and predicts the macroscopic rheology of thermo-rheologically simple vitrimers.
7 citations
References
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TL;DR: By identifying and synthesizing dispersed data on production, use, and end-of-life management of polymer resins, synthetic fibers, and additives, this work presents the first global analysis of all mass-produced plastics ever manufactured.
Abstract: Plastics have outgrown most man-made materials and have long been under environmental scrutiny. However, robust global information, particularly about their end-of-life fate, is lacking. By identifying and synthesizing dispersed data on production, use, and end-of-life management of polymer resins, synthetic fibers, and additives, we present the first global analysis of all mass-produced plastics ever manufactured. We estimate that 8300 million metric tons (Mt) as of virgin plastics have been produced to date. As of 2015, approximately 6300 Mt of plastic waste had been generated, around 9% of which had been recycled, 12% was incinerated, and 79% was accumulated in landfills or the natural environment. If current production and waste management trends continue, roughly 12,000 Mt of plastic waste will be in landfills or in the natural environment by 2050.
7,707 citations
TL;DR: The authors show the double-slit interference effect in the strong-field ionization of neon dimers by employing COLTRIMS method to record the momentum distribution of the photoelectrons in the molecular frame.
Abstract: Wave-particle duality is an inherent peculiarity of the quantum world. The double-slit experiment has been frequently used for understanding different aspects of this fundamental concept. The occurrence of interference rests on the lack of which-way information and on the absence of decoherence mechanisms, which could scramble the wave fronts. Here, we report on the observation of two-center interference in the molecular-frame photoelectron momentum distribution upon ionization of the neon dimer by a strong laser field. Postselection of ions, which are measured in coincidence with electrons, allows choosing the symmetry of the residual ion, leading to observation of both, gerade and ungerade, types of interference.
7,160 citations
TL;DR: In this paper, the authors designed epoxy networks that can rearrange their topology by exchange reactions without depolymerization, and showed that they are insoluble and processable.
Abstract: Permanently cross-linked materials have outstanding mechanical properties and solvent resistance, but they cannot be processed and reshaped once synthesized Non–cross-linked polymers and those with reversible cross-links are processable, but they are soluble We designed epoxy networks that can rearrange their topology by exchange reactions without depolymerization and showed that they are insoluble and processable Unlike organic compounds and polymers whose viscosity varies abruptly near the glass transition, these networks show Arrhenius-like gradual viscosity variations like those of vitreous silica Like silica, the materials can be wrought and welded to make complex objects by local heating without the use of molds The concept of a glass made by reversible topology freezing in epoxy networks can be readily scaled up for applications and generalized to other chemistries
1,901 citations
TL;DR: This mini-review highlights the existing vitrimer systems in the period 2011–2015 with the main focus on their chemical origin.
Abstract: Most covalent adaptable networks give highly interesting properties for material processing such as reshaping, recycling and repairing. Classical thermally reversible chemical cross-links allow for a heat-triggered switch between materials that behave as insoluble cured resins, and liquid thermoplastic materials, through a fully reversible sol–gel transition. In 2011, a new class of materials, coined vitrimers, was introduced, which extended the realm of adaptable organic polymer networks. Such materials have the remarkable property that they can be thermally processed in a liquid state without losing network integrity. This feature renders the materials processable like vitreous glass, not requiring precise temperature control. In this mini-review, an overview of the state-of-the-art in the quickly emerging field of vitrimer materials is presented. With a main focus on the chemical origins of their unique thermal behavior, the existing chemical systems and their properties will be discussed. Furthermore, future prospects and challenges in this important research field are highlighted.
937 citations
TL;DR: The metathesis of dioxaborolanes is reported, which is rapid and thermally robust, and used to prepare vitrimers from polymers as different as poly(methyl methacrylate), polystyrene, and high-density polyethylene that, although permanently cross-linked, can be processed multiple times by means of extrusion or injection molding.
Abstract: Windmills, cars, and dental restoration demand polymer materials and composites that are easy to process, assemble, and recycle while exhibiting outstanding mechanical, thermal, and chemical resistance. Vitrimers, which are polymer networks able to shuffle chemical bonds through exchange reactions, could address these demands if they were prepared from existing plastics and processed with fast production rates and current equipment. We report the metathesis of dioxaborolanes, which is rapid and thermally robust, and use it to prepare vitrimers from polymers as different as poly(methyl methacrylate), polystyrene, and high-density polyethylene that, although permanently cross-linked, can be processed multiple times by means of extrusion or injection molding. They show superior chemical resistance and dimensional stability and can be efficiently assembled. The strategy is applicable to polymers with backbones made of carbon-carbon single bonds.
766 citations