Structural Regulation And Performance Of Thermadapt Recyclable Shape Memory Polythiourethane

Reversible two-way shape memory polymers(2W-SMPs)can achieve reversible changes in different shapes without external stress,and have broad application prospects.However,most reversible 2W-SMPs are thermosetting polymers that cannot be reprocessed and recycled.In addition,it is difficult to obtain complex shapes due to the limitation of the molding and demolding process.The dynamic covalent bonds have been introduced into thermoset SMPs to construct dynamic covalent polymer network(DCPN),which are named as thermadapt SMPs.Thermadapt SMPs combine the reprocessability of thermoplastics with the mechanical strength and thermal stability of thermosets.However,there is currently a lack of systematic studies on the preparation and recycling properties of thermadapt reversible 2W-SMPs.In this paper,from the perspective of molecular structure design,biodegradable polycaprolactone diol(PCL diol),diisocyanate,and pentaerythritol tetrakis(3-mercaptopropionate)(PETMP)were used as raw materials to prepare a series of thermadapt recyclable shape memory polythiourethane cross-linked polymers.The solid-state plasticity,reconfigurability,reversible two-way shape memory effect(2W-SME),self-healing,and reprocessability of the material were explored.And a new method to achieve fully closed-loop recycling of thermoset polymers was discovered.The research contents and conclusions of this paper are as follows:(1)Preparation and performance of thermadapt polycaprolactone polythiourethaneA series of cross-linked polycaprolactone polythiurethane(PCLPTU)with multiple dynamic chemical bonds(ester bonds,urethane bonds and thiourethane bonds)was synthesized using PCL diol(M_n=2000 g/mol)as the soft segment and 4,4’-dicyclohexylmethane diisocyanate(HMDI)and PETMP as the hard segment.PCLPTU had a good thermal stability with an onset thermal decomposition temperature greater than 292.2°C,which could meet the temperature requirement for achieving solid-state plasticity.The presence of multiple dynamic chemical bonds gave PCLPTU solid-state plasticity and reprocessing properties.The internal stress generated by PCLPTU-20%at a fixed strain of 10%could be relaxed to zero at 170°C for 14.6 min.In addition,the tensile strength and elongation at break of the reprocessed samples were higher than those of the original samples.However,PCLPTU had poor crystalline properties and was not easy to achieve shape memory effect.(2)Preparation and performance of thermadapt reversible two-way shape memory polythiourethaneCross-linked polythiourethane(PTU)with good crystallization properties was prepared using PCL diol(M_n=4000 g/mol)as the soft segment and hexamethylene diisocyanate(HDI)and PETMP as the hard segment.Multiple dynamic covalent bonds(ester bonds,urethane bonds and thiourethane bonds)in the cross-linked network combined with self-nucleation crystallization(SNC)endowed the material with good solid-state plasticity,reconfigurability,and reversible 2W-SME.The reversible strain fraction of SNC-treated PTU-20%reached 22.4%.Based on the combination of solid-state plasticity and shape memory,a wide variety of complex 3D permanent shapes could be obtained for the sample without the use of complex molds.PTU/MXene composites prepared by solution dip coating method had excellent photothermal properties and could be prepared as remotely controllable photoresponsive actuators for early warning of abnormal infrared light or abnormal temperature.The PTU designed and prepared in this study had potential applications in complex shape smart actuators.(3)Recycling and closed-loop recovery of thermadapt polythiourethaneBy synthesizing cross-linked PTU with multiple dynamic chemical bonds(ester bonds,urethane bonds and thiourethane bonds),the self-healing,shape-memory assisted self-healing,and reprocessing properties of the materials were systematically investigated,and the feasibility of achieving fully closed-loop recycling was explored.The shape memory effect of the material could speed up the self-healing process.It took 30 min for direct self-healing of scratches on the surface of the material,and only10 min for shape-memory-assisted self-healing.After multiple reprocessing,the reprocessing efficiency of the material was still greater than 100%,showing excellent reprocessing performance.Importantly,the fully closed-loop recycling of the material could be achieved by cleverly leveraging the dynamic exchange of thiourethane bonds at the crosslinking point.Based on this,PTU/carbon nanotubes composites for wearable heaters were further prepared and the separation and recycling of matrix and carbon nanotubes in the composites was achieved.