4.7 Article

Dynamic Polyamide Networks via Amide-Imide Exchange

Journal

MACROMOLECULES
Volume 54, Issue 20, Pages 9703-9711

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.macromol.1c01389

Keywords

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Funding

  1. Dutch Research Council (NWO) [731.016.202]

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The diamide-imide equilibrium was utilized to synthesize dynamic covalent polymer networks with high processibility and processible viscoelasticity at elevated temperatures. The temperature-dependent mechanical properties of the materials were fully reversible, transitioning from elastic solids to predominantly viscous materials around 110 degrees Celsius.
The diamide-imide equilibrium was successfully exploited for the synthesis of dynamic covalent polymer networks in which a dissociative bond exchange mechanism leads to high processibility at temperatures above approximate to 110 degrees C. Dynamic covalent networks bridge the gap between thermosets and thermoplastic polymers. At the operating temperature, when the network is fixed, dynamic covalent networks are elastic solids, while at high temperatures, chemical exchange reactions turn the network into a processible viscoelastic material. Upon heating a dissociative network, the viscosity may also decrease due to a shift of the chemical equilibrium; in such materials, the balance between processibility and excessive flow is important. In this study, a network is prepared that upon heating to above approximate to 100 degrees C dissociates to a significant extent due to a shift in the amide-imide equilibrium of a bisimide, pyromellitic diimide, in combination with poly(tetrahydrofuran) diamines. At room temperature, the resulting materials are elastic rubbers with a tensile modulus of 2-10 MPa, and they become predominantly viscous above a temperature of approximately 110 degrees C, which is dependent on the stoichiometry of the components. The diamide-imide equilibrium was studied in model reactions with NMR, and variable temperature infrared (IR) spectroscopy was used to investigate the temperature dependence of the equilibrium in the network. The temperature-dependent mechanical properties of the networks were found to be fully reversible, and the material could be reprocessed several times without loss of properties such as modulus or strain at break. The high processibility of these networks at elevated temperatures creates opportunities in additive manufacturing applications such as selective laser sintering.

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