Issue 5/2021 - Thermoset shape memory polyimide for closed-loop recycling

Recently, the research group of polymer self-lubricating composites of Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences successfully designed and synthesized thermosetting shape memory polyimide (PI) based on dynamic enamine bonds, realizing full closed-loop recycling
.

Shape memory polyimide has excellent shape memory properties, mechanical properties, thermal stability, chemical resistance, radiation resistance, high and low temperature resistance, etc.
, and has a wide range of application prospects
in flexible electronic devices, high temperature drivers and aerospace fields.
Compared to thermoplastic shape-memory polyimides, thermoset shape-memory polyimides offer superior dimensional stability and creep resistance
.
However, thermosetting polyimide is difficult to melt and dissolve due to the existence of chemical crosslinking network, cannot be reprocessed and recycled, and is difficult to quickly degrade and recover through green methods, resulting in serious waste of resources and environmental pollution
.

The researchers used amine-terminated polyimide oligomers and benzenetricarboxaldehyde polycondensation to form thermosetting polyimides
with reversible dynamic enamine bond crosslinks.
This thermosetting polyimide has a Young's modulus of 1.
8GPa, elongation at break of 10%, and tensile strength of 87MPa, which is comparable
to the high relative molecular weight polyimide of similar structures.
The introduction of dynamic enamine bonds did not reduce the thermal stability
of polyimide.
The thermosetting polyimide also exhibits a good shape memory effect, with a shape fixation rate of 96% and a shape recovery rate of 97%.

The researchers realized the rapid dissociation of thermosetting shape memory polyimide in acidic solution without any catalyst, and obtained thermosetting polyimide film by solvent volatilization, realizing the closed-loop recycling of thermosetting polyimide
.
The comprehensive performance of the remolded thermoset polyimide is comparable to the original, and the strength recovery rate can reach 97%.

Due to its high mechanical strength, thermal stability, shape memory and recyclability, this thermosetting polyimide is a promising multifunctional material
for sustainable recycling.