Metal-coordination crosslinked N-polyindoles as recyclable high-performance thermosets and nondestructive detection for their tensile strength and glass transition temperature

Abstract

Metal coordination crosslinking between stiff N-polyindole chains was constructed, and the crosslinked films exhibited high tensile strength, high heat resistance and excellent polar solvent resistance. The noncovalent crosslinking can be further removed via external pyrophosphate, which endows the crosslinked polymer with a recyclable behavior. The tensile strength and glass transition temperature of the polymers can be nondestructively detected by taking advantage of the fluorescence quenching effect of metal coordination to the adjacent bipyridine structure.

Synthesis of Superheat-Resistant Polyimides with Enhanced Dielectric Constant by Introduction of Cu(ΙΙ)-Coordination

“…Cu per PyMePABZ) in the metal-crosslinked PAAs had been achieved, but the mixture generated gels and lost the fluidity, resulting in weak film-forming capability. The phenomenon was herein assumed to correspond to the insolubility of the stiff crosslinked unit (PyBI-Cu 2+ ) when it reached a certain degree [18]. Neat PI and Cu-PIs were prepared according to Scheme 2.…”

“…Although these successful methodologies led to a great increase of dielectric properties, the former causes the degradation of mechanical properties owing to the phase segregation of fillers and the latter brings the reduced thermal properties with the employment of flexible blocks (e.g., ether linkage). Differently, the supramolecular polymers that exploit metal-ligand interactions, possess high dielectric constant because of the improved permanent dipoles caused by metal atoms [16,17], and the metal-crosslinking can further improve their thermal and mechanical properties [17,18].…”

Recyclable and Dual Cross‐Linked High‐Performance Polymer with an Amplified Strength–Toughness Combination

“…However, these reversible non‐covalent bonds could be easily deconstructed and reconstructed in soft polymer materials, in which polymer chain segments are easy to move from one conformation to another, but difficult to move in a rigid polymer system, resulting in difficulty in dissipating energy in rigid high‐performance polymers. According to our previous work,13 single Cu 2+ ‐coordination crosslinks greatly contribute to enhancing the strength of high‐performance polymers, but are less effective at improving extensibility (still brittle fracture, ε < 9%) caused by weak segment mobility and poor energy dissipation across rigid polymers 14. It is difficult to build tough, rigid, high‐performance polymers using supramolecular chemistry.…”

“…The precursors (i and ii) and PAEK copolymers with different molar fractions of BTA and PBI units were synthesized using a previously published procedure;13a see the Supporting Information for details. The characterization of the precursors and polymers is detailed in the Supporting Information, and the results agreed with the proposed structures (Figures S3–S11, Supporting Information).…”

“…Cu 2+ ‐coordination bonds formed between Cu 2+ and ligands (BTA and PBI), as confirmed by the UV–vis spectra and 3D fluorescence spectra. An obvious redshift of the UV–vis absorption spectrum was induced by Cu 2+ in BP‐40‐20‐25 films due to the formation of the Cu 2+ ‐coordination bond (Figure 3c) 13. Moreover, the decreased fluorescence intensity of BTA (Figure 3d, E x : 530 nm, E m : 460 nm) and PBI (Figure 3e, E x : 579 nm, E m : 380 nm) with titration reflected that the formation of Cu 2+ ‐coordination bonds (Figure 3d,e) 13,17e…”