Thermomechanical insight into the reconfiguration of Diels–Alder networks

Pratchayanan, Danaya; Yang, Jeh‐Chang; Lewis, Christopher L.; Thoppey, Nagarajan; Anthamatten, Mitchell

doi:10.1122/1.4997580

Cited by 22 publications

(13 citation statements)

References 34 publications

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“…This was confirmed through variable-temperature Fourier transform-infrared (FT-IR) spectroscopy, which indicated that the dissociation of EAE and IPAE HUBs remained below 1% up to 170 °C, while the dissociation of TBAE reached ∼8% at 130 °C. Importantly, similar behavior has also been observed for other CAN chemistries and topologies, such as chaingrowth networks with reversible crosslinks pendent to the backbone 42,59,62 and pure step-growth materials. 29−32 Finally, stress relaxation of TBAE, EAE, and IPAE networks in the range of their rubbery plateau scaled according to an Arrhenius relationship, with lower E a values calculated for bulkier HUB substituents (Figure 4D).…”

Section: Dissociative Canssupporting

confidence: 68%

“…The crosslink density in thermoreversible dissociative CANs inevitably decreases with increasing temperature, as dictated by the temperature-dependent dynamic equilibrium (Figure B). However, isochronal dynamic mechanical analysis of various thermoreversible dissociative CAN systems (e.g., hindered urea, 1,2,3-triazolium, , nitroxide, DA, , acetoacetyl amide, or oxime-carbamate networks) revealed a rubbery plateau of constant modulus between the glass transition and the gel point (Figures , , and ). This suggests that, since the modulus at the rubbery plateau can be related to the network’s crosslink density, K eq at these temperatures is large and strongly favors crosslink association.…”

Section: Dissociative Cansmentioning

confidence: 99%

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Adaptable Crosslinks in Polymeric Materials: Resolving the Intersection of Thermoplastics and Thermosets

et al. 2019

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The classical division of polymeric materials into thermoplastics and thermosets based on covalent network structure often implies that these categories are distinct and irreconcilable. Yet, the past two decades have seen extensive development of materials that bridge this gap through incorporation of dynamic crosslinks, enabling them to behave as both robust networks and moldable plastics. Although their potential utility is significant, the growth of covalent adaptable networks (CANs) has obscured the line between “thermoplastic” and “thermoset” and erected a conceptual barrier to the growing number of new researchers entering this discipline. This Perspective aims to both outline the fundamental theory of CANs and provide a critical assessment of their current status. We emphasize throughout that the unique properties of CANs emerge from the network chemistry, and particularly highlight the role that the crosslink exchange mechanism (i.e., dissociative exchange or associative exchange) plays in the resultant material properties under processing conditions. Predominant focus will be on thermally induced dynamic behavior, as the majority of presently employed exchange chemistries rely on thermal stimulus, and it is simple to apply to bulk materials. Lastly, this Perspective aims to identify current issues and address possible solutions for better fundamental understanding within this field.

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Section: Dissociative Canssupporting

confidence: 68%

Section: Dissociative Cansmentioning

confidence: 99%

Adaptable Crosslinks in Polymeric Materials: Resolving the Intersection of Thermoplastics and Thermosets

et al. 2019

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“…Every dissociative CAN for which SRA measurements were reported at multiple temperatures demonstrated the Arrhenius relationship typically associated with vitrimers. 16 , 24 , 27 , 56 − 58 , 60 − 67 Table 2 summarizes these findings, including the type of dissociative exchange chemistry, catalyst if used, the temperature range for SRA, and the E a , calculated from the Arrhenius plot. Notably, both the temperature at which these experiments were performed and the calculated E a values were in a similar range to those of associative CANs.…”

Section: Dissociative Cans Also Exhibit Arrhenius Relationships Betwementioning

confidence: 93%

“… 14 A classic, unambiguous example of a dissociative CAN is a network cross-linked by Diels–Alder (DA) adducts ( Figure 2 A). 15 , 16 Upon heating, the rate of the retro-DA reaction increases with respect to the forward-DA reaction, which first leads to network rearrangement and can eventually induce a gel-to-sol transition. 17 In 2011, Leibler and co-workers reported a prototypical associative CAN, a cross-linked polyester that was thermally reprocessed via transesterification ( Figure 2 B).…”

Section: Introductionmentioning

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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“…Formation of the reversible covalent networks from DA type monomers or cross-linking of polymers containing pendant functional groups is widely studied [1,12,13,14,15,16,17,18,19,20]. Reversibility of cross-linking is usually investigated by sol–gel analysis [21] or by DMA and rheology experiments [3,12,13,22,23,24]. The formation of the thermoreversible networks is characterized by the critical temperature for gelation, T gel .…”

Section: Introductionmentioning

confidence: 99%

Control of Gelation and Properties of Reversible Diels–Alder Networks: Design of a Self-Healing Network

2019

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Reversible Diels–Alder (DA) type networks were prepared from furan and maleimide monomers of different structure and functionality. The factors controlling the dynamic network formation and their properties were discussed. Evolution of structure during both dynamic nonequilibrium and isothermal equilibrium network formation/breaking was followed by monitoring the modulus and conversion of the monomer. The gelation, postgel growth, and properties of the thermoreversible networks from tetrafunctional furan (F4) and different bismaleimides (M2) were controlled by the structure of the maleimide monomer. The substitution of maleimides with alkyl (hexamethylene bismaleimide), aromatic (diphenyl bismaleimide), and polyether substituents affects differently the kinetics and thermodynamics of the thermoreversible DA reaction, and thereby the formation of dynamic networks. The gel-point temperature was tuned in the range Tgel = 97–122 °C in the networks of the same functionality (F4-M2) with different maleimide structure. Theory of branching processes was used to predict the structure development during formation of the dynamic networks and the reasonable agreement with the experiment was achieved. The experimentally inaccessible information on the sol fraction in the reversible network was received by applying the theory. Based on the acquired results, the proper structure of a self-healing network was designed.

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Thermomechanical insight into the reconfiguration of Diels–Alder networks

Cited by 22 publications

References 34 publications

Adaptable Crosslinks in Polymeric Materials: Resolving the Intersection of Thermoplastics and Thermosets

Adaptable Crosslinks in Polymeric Materials: Resolving the Intersection of Thermoplastics and Thermosets

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

Control of Gelation and Properties of Reversible Diels–Alder Networks: Design of a Self-Healing Network

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