The Design And Research Of An Intermolecular Mechanochemical Reaction Cascade For Polymer Crosslinking

A major aspiration of contemporary polymer mechanochemistry is to reproduce aspects of the sophisticated response of living tissue to mechanical load in synthetic materials.Both types of materials degrade under mechanical load,but only the living tissue can sense and signal this damage,and trigger its repairs.Damage-signaling in synthetic materials is generally achieved by exploiting mechanochromism,or mechanically-triggered changes in the absorption or emission properties of a material.Here we demonstrate an intermolecular reaction cascade to control the force which triggers crosslinking,a cascade consisting of three reactions:reversible ring opening of spirothiopyran,anthracene-maleimide cleavage,and the addition reaction between spirothiopyran and maleimide.The main idea of this project is to control the crosslinking process between a high-threshold-force mechanophore and the cross-linker by the cleavage process of low-threshold-force mechanophore.The masking of maleimide is achieved by the anthracene-maleimide mechanophore,and then the maleimide cross-linker is released.At the same time,the spirothiopyran polymer transforms to merocyanine by force and it undergoes an addition reaction with maleimide to form a crosslinking system.In addition to the functions of colour change,force-induced luminescence and forceinduced crosslinking,the crosslinking system increases the threshold force.And the degree of crosslinking can be controlled by the anthracene-maleimide cleavage process.As a result,this intermolecular cascade provides a means of limiting the occurrence of irreversible crosslinking to overstressed volumes of the loaded material that are at the highest risk of failure.