Preparation And Characterization Of Polyimide Precursor Hydrogel

The development of wearable devices,soft robots,and electronic skin requires strain sensors that integrate multiple functionalities,such as being stretchable,self-healable,and biocompatible.For most of the current hydrogels,the problems such as the use of organic solvent preparation,poor mechanical properties,no self-repairing ability or self-repair requires severe conditions,we prepared a fully aromatic polyamic acid salt?PAAS?hydrogel using a novel and simple approach.This paper establishes an environmentally friendly green synthesis method for synthesizing PAAS hydrogel with high molecular weight and aromatic main structure in aqueous solution.P-phenylenediamine?PDA?and 3,3',4,4'-biphenyltetracarboxylic dianhydride?s-BPDA?were used to prepare a fully aromatic backbone hydrogel via gradual polymerization.To improve the mechanical properties of hydrogels and to increase the storage modulus?G??,we introduced trifunctional monomers as chemical cross-links and calcium ions(Ca²⁺)as physical cross-links.The prepared hydrogel was characterized using 1H nuclear magnetic resonance?1H NMR?and Fourier transform infrared?FTIR?spectroscopy,gel-permeation chromatograph?GPC?,dynamic rheometry?DHR?and universal tensile testing machine.The obtained PAAS hydrogel exhibits excellent stretch ability and has an elongation rate of about 1350%.It can also rapidly self-heal and return to the original mechanical strength without needing any external stimuli.In addition,the PAAS hydrogel has excellent temperature responsiveness.When used as a strain sensor,the PAAS hydrogel has a sensitive electrical resistance response even after 200 cycles and adhesiveness to various surfaces,especially human skin.To the best of our knowledge,this is the first time to prepare a high-performance polyimide?PI?precursor hydrogel that can be used as a raw material for PI aerogel.Because of its superb overall performance,low preparation cost,efficient preparation,and environmentally friendliness,the PAAS hydrogel is highly suitable for use as sensitive strain sensors for applications in motion detection.