Reprocessing Cross-linked Polyurethanes by Catalyzing Carbamate Exchange

Fortman, David J.; Sheppard, Daylan T.; Dichtel, William R.

doi:10.26434/chemrxiv.8243063

Cited by 18 publications

(26 citation statements)

References 2 publications

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“…The relaxation activation energy of ACPCN41151 (E a = 86.75 kJ mol À1 , Fig. 3d) was in the middle position of the reported dynamic exchange systems, 29,30,[46][47][48][49][50] which meant that the azine-containing materials could be applied in most daily or industrial circumstances and at the same time they could be reprocessed under comparatively mild conditions. The analysis of creep resistance was performed to further confirm the heat resistance of the ACPCNs.…”

Section: Dynamic Properties Of Acpcnsmentioning

confidence: 91%

Mechanically robust, creep-resistant, intrinsic antibacterial and reprocessable dynamic polyurethane networks based on azine moieties

Han

Zhou

Bai

et al. 2022

Mater. Chem. Front.

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Section: Dynamic Properties Of Acpcnsmentioning

confidence: 91%

Mechanically robust, creep-resistant, intrinsic antibacterial and reprocessable dynamic polyurethane networks based on azine moieties

Han

Zhou

Bai

et al. 2022

Mater. Chem. Front.

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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%

“…In the presence of a transition metal catalyst at elevated temperatures, the urethanes partially revert into alcohols and isocyanates, as demonstrated by small molecule studies ( Figure 5 A). 56 Nevertheless, these cross-linked materials display the properties typical of vitrimers. A DMTA trace, collected to elevated temperatures for this Outlook, reveals a rubbery plateau of constant modulus between 80 and 160 °C ( Figure 5 B).…”

Section: Dissociative Cans Also Exhibit Arrhenius Relationships Betwementioning

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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“…We next evaluated the generality of using 3 as a reactive filler in CANs that relax stress via urethane exchange. Polyurethanes have previously been shown to have rapid stress relaxation in the presence of tin (IV) catalysts, 30,31 which was proposed to occur through the partial reversion of carbamates to isocyanates and alcohols. We designed a network comprised of hexamethylene diisocyanate, a short chain PEG (M n = 400 g/mol), along with a 4-arm PEG star (M n = 800 g/mol) macromonomer and 3 as crosslinkers.…”

Section: Resultsmentioning

confidence: 99%

Incorporating Functionalized Cellulose to Increase the Toughness of Covalent Adaptable Networks

Swartz

Dichtel

2020

ACS Appl. Mater. Interfaces

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Covalent adaptable networks (CANs) are cross-linked polymers that have mechanical properties similar to thermosets at operating conditions, yet can be reprocessed by cross-link exchange reactions that are activated by a stimulus. Although CAN exchange dynamics have been studied for many polymer compositions, the tensile properties of these demonstration systems are often inferior compared to commercial thermosets. In this study, we explore toughening CANs capable of forming covalent bonds with a reactive filler to characterize the trade-off between improved toughness and longer reprocessing times. Polycarbonate (PC) and polyurethane (PU) CANs were toughened by incorporating cellulose modified with cyclic carbonate groups as a reactive filler with loadings from 1.3-6.6 wt%. The addition of 6.6 wt% of the cellulose derivative resulted in a 3.2-fold increase in average toughness for the PC CANs, yet only increased the characteristic relaxation time of stress relaxation (*) via disulfide exchange at 180 °C from 63 s to 365 s. The cellulose-containing samples also showed >80% recovery in crosslinking density and mechanical properties after reprocessing. The addition of 3.2 wt% of the functionalized cellulose into a PEG-based PU CAN led to a 2.3-fold increase in toughness, while increasing * at 140 °C from 106 s to 157 s. These findings demonstrate the promise of functionalized cellulose as an inexpensive, renewable, and sustainable filler that toughens CANs containing hydroxyl groups. File list (3) download file view on ChemRxiv 2020_03_ChemRxiv_Swartz_Manuscript.pdf (1.31 MiB) download file view on ChemRxiv 2020_03_ChemRxiv_Swartz_TOC.jpg (68.46 KiB) download file view on ChemRxiv 2020_03_ChemRxiv_Swartz_Supporting_Information.pdf (5.12 MiB)

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Reprocessing Cross-linked Polyurethanes by Catalyzing Carbamate Exchange

Cited by 18 publications

References 2 publications

Mechanically robust, creep-resistant, intrinsic antibacterial and reprocessable dynamic polyurethane networks based on azine moieties

Mechanically robust, creep-resistant, intrinsic antibacterial and reprocessable dynamic polyurethane networks based on azine moieties

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

Incorporating Functionalized Cellulose to Increase the Toughness of Covalent Adaptable Networks

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