A Highly Stretchable And Self-healing Elastomer Based On A Dual Crosslinking Of Polyrotaxanes And Hydrogen Bond

Highly stretchable elastomer materials are widely used in the field of flexible electronics.The rapid development of stretchable electronics has been putting forward requirements for polymers with higher mechanical properties.Meanwhile,the stretchable electronics are likely to crack or even break when used frequently.Hence,it is also important to render materials self-healing properties.However,high-strength elastomers crosslinked with covalent bonds like commercial Sylgard 184 can hardly autonomously self-heal and usually possess low stretchability.For some elastomers based on dynamic non-covalent bonds(such as hydrogen bonds,coordination bonds,etc.),they can achieve higher elongation at break and higher self-healing efficiency,but their strain at break is often lower.Therefore,it still remains challenging to prepare highly stretchable elastomers with good mechanical property(elongation at break and strain at break)and self-healing ability at the same time.In this paper,a dual crosslinked elastomer based on polyrotaxanes and hydrogen bonds was synthesized.The elastomer can achieve good mechanical property and self-healing property.Our main work is shown as follows:(1)Firstly,two cyclodextrin-based polyrotaxanes were synthesized.PEG and PDMS were used as guest macromolecules,and a-cyclodextrin and y-cyclodextrin were used as cyclic host molecules.Then,the average number of cyclodextrins on each polymer chain was calculated by 1H NMR,GPC and TGA.Besides,the two polyrotaxanes were acetylated subsequently in order to improve the solubility in most solvents,and the acetylated polyrotaxanes were soluble in common organic solvents,which provided a basis for the preparation of subsequent functional materials.(2)PEG polyrotaxanes was introduced into PDMS polyurea elastomer to enable the materials cross-linked by hydrogen bonds and polyrotaxanes.Among the samples,PR-PDMS-2 possesses excellent mechanical properties.The elongation at break can reach 2800%while the fracture stress can reach 1.05 MPa(20 mm/min),and the material also possesses good resilience and high toughness(19.4 J/m3).By synthesizing a variety of contrast elastomers,we can conclude that a large number of hydrogen bonds in the system endowed the material with a certain mechanical strength,and the introduction of polyrotaxanes could make the material dissipate energy synergistically with hydrogen bonds under external force,thereby increasing the stretchability of the material.In terms of self-healing property,the effects of temperature and healing time on the self-healing efficiency of PR-PDMS-2 were studied respectively.Finally,it was concluded that the material could achieve high self-healing e fficiency(93%)after 48 hours at 55 °C'(3)Various methods were systematically adopted to prove the sliding effect of polyrotaxanes.The differences between AP-PDMS-2 and PR-PDMS-2 were compared by conducting tensile tests under higher temperatures,step extension and in-situ SAXS experiments,which further provided a strong theoretical basis for explaining the excellent mechanical properties of PR-PDMS-2.(4)Finally,a stretchable conductor was prepared based on the above highly stretchable self-healable elastomer and the conductor was further used to fabricate a strain sensor.The GF(gauge factor)of the sensor can reach 1488 at the strain of 77%.Besides,the sensor can also be applied to detect human movements such as fingerbending,arm muscles and wrist muscles.