Study On The Preparation And The Self-healing Properties Of The Cross-linked Polyurethane Based On Diels-alder Reaction

In the natural world, most creatures can repair and heal independently after local injury, but synthetic polymer material does not have this "self-healing" ability. Those polymer materials are vulnerable to the effects of mechanical, ultraviolet radiation and chemical substances in the process of using or processing, resulting in the appearance of the micro-cracks in the surface and interior of those materials. Those micro-cracks on the surface of the material are easy to be repaired, but those internal micro-cracks are hard to detect and let alone to repair. The existences of these micro-cracks lower the material performance and service life and even make them complete loss. Early in the 21 st century, simulating biological self-healing mechanism, the foreign researchers prepared the smart materials with the ability of self-diagnosis and self-healing by introducing self-healing mechanism into the polymer. The mechanical performance and service life of this smart material have been better improved. Self-healing technology has a good prospect in microelectronic polymers, medical biomimetic materials, military materials, construction materials and other aspects, and become one of the most popular research topic in the preparing of intelligent polymer materials. There are so many methods to prepare the self-healing materials, but one of the most effective methods is to introduce the reversible covalent bond into the polymer materials. As the first choice of the reversible covalent reaction to prepare the self-healing material, Diels-Alder(DA) reaction has many advantages, such as, mild reaction conditions, temperature reversible, the promotion of an aqueous solution and no catalyst is needed. The polymer materials, which were implant Diels-Alder covalent bonding in the molecular chains, can exhibit a good self-healing performance in the polymer‘s damage place via retro Diels-Alder reaction(retro-DA) and Diels-Alder reaction. The self-healing polymer material containing DA bond has a higher self-healing efficiency and the self-healing system can perform self-healing several times in the same damaged position.In this paper, we firstly prepared the polyurethane prepolymer end-capped with furan rings(TNDF) by designing the molecular chains. Then we synthesized the polyurethane MPA by using the furan ring and maleimide as the DA reaction group. The linear polyurethane was tested by FT-IR, GPC, DSC, DMA, POM and tensile test method. The DSC and DMA test results show that the DA reation and r-DA reaction of MPA polyurethane occured at 65℃~87℃ and 107.9℃~138.3℃ separately, and the glass transition temperature of the MPA polyurethane is-42.6 ℃. GPC test showed that the number average molecular weight of MPA was 35512 and PD was 1.147. We also used the POM to observe the self-healing process of the MPA polyurethane, and the result showed that the cracks of MPA polyurethane could be filled completely after 3hours‘ self-healing at 90℃.The self-healing efficiency of MPA polyurethane, which was tested by the tensile test could reach to 73%.We also prepared the cross-linked polyurethane materials HTK-PU by designing the molecular chain structure with DA group as the crosslinking point of these polyurethane materials. The cross-linked polyurethane was tested by FT-IR, DSC, DMA, POM, tensile test and swelling property test method. The DSC and DMA test results showed that the DA reation and r-DA reaction of HTK-PU polyurethane occured at 57.08 ℃~ 87.10 ℃ and 87.10 ℃~ 110 ℃ separately, and the glass transition temperature of the HTK-PU polyurethane was 54.86 ℃. The swelling experiment showed that the HTK-PU polyurethane was swelling and insoluble in DMF at 70℃, but it could completely dissolve in DMF at 90℃. The self-healing process of the HTK-PU polyurethane was also observed by the POM, and the result showed that the cracks of HTK-PU polyurethane could be filled completely after 12 hours‘ self-healing at 95℃. The self-healing efficiency of HTK-PU polyurethane, which was tested by the tensile test could reach to 67.56%. However, the hardness of this material is very high(shore D80), and the toughness is poor. In order to improve corresponding mechanical properties, we firstly prepared the TA resin and polyurethane prepolymer end-capped with furan rings(IDI-TA) by re-designing the molecular chains. And then we got the cross-linked polyurethane materials ITB-PU(The soft segment content was 11.5%) with good mechanical properties by the reaction of N,N’-(4,4’-methylenediphenyl) dimaleimide(BMI) and IDI-TA. We studied on the thermoreversibility of the cross-linked polyurethane ITB-PU by FT-IR, DSC, DMA, swelling experiments and other analytical testing methods, and we observed the self-healing process of ITB-PU by using POM at 80℃. The DSC and DMA test results showed that the DA reation and r-DA reaction of ITB-PU polyurethane occured at 50.33℃ and 69.55℃ separately, and the glass transition temperature of the ITB-PU polyurethane was-14.7 ℃.The swelling experiment showed that the ITB-PU polyurethane was swelling and insoluble in DMF at 50℃ and 60℃, but it could completely dissolve in DMF at 70 ℃. The self-healing process of the ITB-PU polyurethane was also observed by the POM, and the result showed that the cracks of ITB-PU polyurethane could be filled completely after 6 hours‘ self-healing at 80℃. The self-healing efficiency of the repaired specimens after 12 hours,self-healing could reach to 80.02%.