Malleable, Recyclable, and Robust Poly(amide–imine) Vitrimers Prepared through a Green Polymerization Process

Abstract

The introduction of dynamic covalent bonds into chemically cross-linked networks is an effective strategy to solve intrinsic problems of inability to be reprocessed or recycled for thermosetting polymers. Imine bonds (also known as Schiff bases) are promising candidates for constructing covalent adaptable networks (CANs) because of their easily triggered exchange reactions. However, it remains a challenge for polyimine vitrimers to improve the creep resistance and thermal stability due to their unstable imine-based networks. In this work, we report a green strategy to prepare a series of partially bio-based, malleable, recyclable, and robust poly­(amide–imine) vitrimers by bulk polymerization for the first time. The amide bonds are introduced into polyimine vitrimers for the improvement of mechanical property, thermal stability, and creep resistance. A series of H2N-terminated prepolymers with tunable structures were first synthesized, which combined the amide and imine groups together. Then, a bio-based trimethyl citrate was selected as the curing agent to react with H2N-terminated prepolymers for the construction of CANs with amide bonds as cross-linking points. The imine groups accompanied by a dynamic exchange nature endowed the poly­(amide–imine) vitrimers with reprocessability, self-healing property, and degradability. Meanwhile, the amide groups with inherent intermolecular hydrogen bonding enhanced the mechanical properties, thermal stability, and creep resistance of poly­(amide–imine) thermosets.

Rapid Stress Relaxation, Multistimuli-Responsive Elastomer Based on Dual-Dynamic Covalent Bonds and Aniline Trimer

“…When the relaxation times were applied in an Arrhenius plot, a linear relationship was observed as shown in Figure d, and the activation energy was calculated to be around 36 ± 1 kJ mol –1 . Interestingly, the calculated activation energy was lower than the reported activation energies of either solely used boronic esters − or imine bonds (38–157 kJ mol –1 ) − as the dynamic cross-links. It could be deduced that this combination of two DCBs (boronic esters, imine bonds) was much more efficient than the sole one in term of stress relaxation.…”

Biobased, High-Performance Covalent Adaptable Networks from Levulinic Acid and Amino Acids

“…Under acid catalysis, Schiff base-based thermosets can be hydrolyzed to generate oligomers with amino and aldehyde groups. 56,57 It was established that LAE-GLU and LAE-LYS could be degraded in mild acidic environments without the need of an organic solvent, which was in keeping with sustainable development principles. The structure of the amino acids also had an impact on the rate of degradation.…”

Thermal Reprocessing and Closed‐Loop Chemical Recycling of Styrene‐Butadiene Rubber Enabled by Exchangeable and Cleavable Acetal Linkages

“…Hence, these thermosetting materials can achieve malleability and reprocessability like thermoplastics. Until now, various kinds of dynamic covalent bonds, such as 𝛽-hydroxy ester, [9,11,12] disulfide, [13] imine, [14][15][16] boroxine ester, [17][18][19] silyl ether, [20][21][22] acetals, [23][24][25] vinylogous urethanes, [26][27][28] hindered urea, [29][30][31] diketoenamine, [32,33] and 1,2,3-triazolium, [34][35][36] etc. have been utilized to develop CANs or vitrimers.…”