Temperature Dependent Stress Relaxation in a Model Diels–Alder Network

Sheridan, Richard J.; Adzima, Brian J.; Bowman, Christopher N.

doi:10.1071/ch11176

Cited by 17 publications

(18 citation statements)

References 24 publications

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“…Such polymers combine the desirable attributes of conventional thermosets with malleability and recyclability. [3][4][5][6][7][8] CANs are classied into two types, where the dynamic structures are achieved either by reversible depolymerization with equilibrium shiing, as in the classic Diels-Alder (DA) reaction, [9][10][11][12][13] or through the recently developed bond exchange reactions (BERs). No matter which mechanism is chosen, CANs exhibit two features not found in traditional thermosetting polymers: malleability resulting from signicant stress relaxation, [14][15][16] and surface welding.…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics studying on welding behavior in thermosetting polymers due to bond exchange reactions

Yang

et al. 2016

RSC Adv.

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Covalent adaptable network (or dynamic covalent network) polymers can alternate their network topology through bond exchange reactions, whereby an active atom replaces an atom in an existing bond, resulting in a new bond and a new active atom. This process repeats itself numerous times in the network, bestowing interesting material behaviors, such as stress relaxation, surface welding, self-healing and recycling, upon the network. In this paper, molecular dynamics simulations are used to investigate surface welding due to bond exchange reactions in an epoxy system. Two epoxy networks are constructed and brought into contact, and bond exchange reactions are then activated. The trajectory of active atoms is tracked, which shows how the active atoms cross the interface. Based on simulation results, this work analyzes the influence of welding conditions, such as welding time, welding temperature, degree of polymerization and crosslinking density of original networks, on the mechanical properties of welded materials. These parameters determine the number of connected bonds on the interface, which consequently affects the welding performance. Eventually, with a sufficiently long welding time, the system can fully recover the same modulus and yielding stress as those of a fresh network. Finally, the active atoms' penetration depth, obtained from MD simulation, shows good agreement with the predictions of some existing theories.

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Section: Introductionmentioning

confidence: 99%

Molecular dynamics studying on welding behavior in thermosetting polymers due to bond exchange reactions

Yang

et al. 2016

RSC Adv.

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“…Compound (5) was prepared as described in [16] , and (8) was adapted from procedures described in. [17] …”

Section: Methodsmentioning

confidence: 99%

3D Photofixation Lithography in Diels–Alder Networks

Adzima

Kloxin

DeForest

et al. 2012

Macromol. Rapid Commun.

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3D structures were written and developed in a crosslinked polymer initially formed by a Diels–Alder reaction. Unlike conventional liquid resists, small features cannot sediment, as the reversible crosslinks function as a support, and the modulus of the material is in the MPa range at room temperature. The support structure, however, can be easily removed by heating the material which depolymerizes the polymer into a mixture of low-viscosity monomers. Complex shapes were written into the polymer network using two-photon techniques to spatially control the photoinitiation and subsequent thiol–ene reaction to selectively convert the Diels–Alder adducts into irreversible crosslinks.

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“…), the aggregate connectivity of the network is static, even while the chains themselves dynamically break and reform. The effect is that the network topology evolves over time, and when such materials are subjected to mechanical stresses, relaxation is observed, and the permanent shape of the material evolves [24,10,6,32]. Another important effect is that the network has a thermally tunable set of cross-links and therefore, a thermally tunable number density of chains, which arises due to the temperature dependence of the Diels-Alder chemical equilibrium.…”

Section: 1038/nmat2891mentioning

confidence: 99%

“…However, specific functionalities have been included along their polymer chains and cross-linking sites, and these functionalities undergo thermally stimulated, reversible chemical reactions that connect or disconnect chains from the network [15,37,34]. An actively explored chemistry in the literature integrates furan and maleimide functionalities that undergo the highly reversible, Diels-Alder (DA) cycloaddition reaction along polymer chains and at cross-linking sites [24,33,6,26,32]. In such networks, these functional groups behave as dynamic bonds that break and reform over time.…”

Section: Introductionmentioning

confidence: 99%

The mechanics of network polymers with thermally reversible linkages.

Long¹

2012

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Encapsulated printed circuit boards typically use conventional thermosetting polymers which are difficult to remove without damaging the electronics if upgrades are needed. To improve the efficiency of maintaining printed circuit boards, network polymers with thermally reversible linkages were developed to provide an alternative class of encapsulation thermosets that could be easily and non-destructively removed and later reapplied. These polymers include functionalities that dynamically break and form covalent bonds. Over time, the connectivity of the network evolves, which causes the macroscopic stress in the material to relax and the permanent shape to change even if these processes are in equilibrium. With respect to removal, the equilibrium behavior of these processes changes if the thermodynamic state of the material is changed, which alters the number density of chains. If the number density of chains is reduced below the percolation threshold, the material exhibits a gel-point transition beyond which, it behaves as a viscous liquid. These two properties contrast sharply with conventional thermosetting polymers, which do not exhibit this relaxation mechanism nor a gel-point transition.To take advantage of such novel material capabilities at length scales relevant to electronics packaging, a continuum-scale constitutive model is needed that correctly accounts for the thermalchemical-viscoelastic behavior of such materials, especially since the state of the art for using 3 them is limited to experimental investigations. To meet this need, a continuum-scale, thermodynamically consistent free energy description of such materials is developed in this work. Paired with this free energy are non-equilibrium contributions associated with the topological rearrangement of the network as chains are added and removed as well as viscoelasticity. The model is calibrated and validated against experimental data published in the literature. Finally, simple encapsulation thermal-mechanical scenarios are examined that demonstrate a substantial difference in behavior between conventional polymer networks vs. those with thermally reversible linkages.4 Acknowledgment

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Temperature Dependent Stress Relaxation in a Model Diels–Alder Network

Cited by 17 publications

References 24 publications

Molecular dynamics studying on welding behavior in thermosetting polymers due to bond exchange reactions

Molecular dynamics studying on welding behavior in thermosetting polymers due to bond exchange reactions

3D Photofixation Lithography in Diels–Alder Networks

The mechanics of network polymers with thermally reversible linkages.

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