| Because of its excellent mechanical properties,high and low temperature resistance,chemical stability and processing properties,polyurethane is widely used in the fields of binder materials,packaging materials,sealing materials and so on.However,in some specific occasions,such as as packaging materials for photovoltaic modules,due to longterm exposure to the outside,in the process of transportation,storage and use,it is easy to produce microcracks,these microcracks are difficult to naked eye detection and manual repair,which will reduce the use of polyurethane function and easy to cause safety problems.In recent years,the newly developed self-healing polymer material,as a new type of intelligent material,can repair the micro-cracks independently under certain conditions,thus improving the safety and prolonging the service life.Therefore,the research on the self-healing function of polyurethane while keeping the original excellent properties of polyurethane as much as possible has become a research hotspot in the fields of chemistry and materials.This paper designed and synthesized a series of dynamic disulfide bond containing polyurethane-amide polymers,widely studied hard segment structure is asymmetric alicyclic structure of isophorone diisocyanate(IPDI),six methylene linear aliphatic diisocyanate(HDI),asymmetric aromatic ring structure of toluene diisocyanate(TDI),symmetric structure of aromatic ring of diphenyl methane diisocyanate(MDI),containing disulfide bond structure of chain extender on the polymer mechanics performance,thermal performance,the influence law of self-healing performance,fixing temperature were also discussed,the relationship between the repair time and the repair efficiency.The main research contents and results are as follows:(1)Four polyurethane-amides containing dynamic disulfide bonds were synthesized using IPDI,HDI,TDI and MDI as hard segments,polyadipate-1,4-butanediol ester diol PBA as soft segments,3,3’-dithiodipropionic acid DPA as chain extender,respectively.The results showed that the polyurethane-amides synthesized by isoporone diisocyanate with asymmetric adipocyclic structure had the best self-healing properties,and the polyurethane-amides synthesized by aromatic structure TDI and MDI had the best tensile strength.The self-healing efficiency of PU1 synthesized by IPDI,PBA and DPA can reach90.29% under 75 ℃ for 4 hours,and its initial strength can reach 8.380 MPa.The tensile strength of PU2 synthesized by TDI,PBA and DPA is up to 26.174 MPa,and the tensile strength of PU2 is more than 3 times that of PU1.The self-healing efficiency of PU2 can reach 46.62% when it is repaired at 75 ℃ for 4 hours.The tensile strength of PU3 synthesized by HDI,PBA and DPA is 8.323 MPa,and the self-healing efficiency of PU3 can reach 65.99% when repaired at 75 ℃ for 4 hours.The tensile strength of PU4 synthesized by MDI,PBA and DPA is 25.498 MPa,and the self-healing efficiency of PU4 can reach 34.16% after being repaired at 75 °C for 4 hours.(2)Four polyurethane-amides containing dynamic disulfide bonds were synthesized using 2,2’-dithiobenzoic acid(DBA)as chain extender under the condition of the structure of soft and isocyanate unchanged.The results showed that the structure of chain extender had influence on the tensile strength and the self-healing efficiency of the polyurethane-amide,in particular,the effect on self-repair efficiency is particularly significant.The tensile strength of PU5 synthesized by IPDI,PBA and DBA is 11.053 MPa,which is 2.673 MPa higher than PU1.The self-healing efficiency of PU5 can reach63.33% under 75 ℃ for 4 hours,and is 26.96% lower than that of PU1.The tensile strength of PU7 synthesized by IPDI,PBA and DBA is 5.494 MPa,which is 2.829 MPa lower than that of PU3.The self-healing efficiency of PU7 can reach 14.18% and 51.81%lower than that of PU3 when it is repaired at 75 ℃ for 4 hours.(3)The relationship between repair process and repair efficiency was discussed by changing repair temperature and repair time.The results show that the self-healing efficiency of the tensile strength of polyurethane-amide is directly proportional to the healing temperature and the healing time.When PU1 was repaired at 25 °C,50 °C and75 °C for 4 hours,the self-healing efficiency of tensile strength was 26.33%,82.00% and92.29%,respectively.The self-healing efficiency of tensile strength of PU1 was 19.09%,45.22%,71.63%,90.29%,90.96% and 91.02% under 75 ℃ for 1,2,3,4,5 and 6 h,respectively.(4)A polyurethane-amide composite structure was synthesized by using the mixture of IPDI and TDI as the hard segment.The results show that the initial tensile strength of PU1 is 16.115 MPa,which is nearly one time higher than that of PU1.At the same time,the self-repairing efficiency is obviously improved.The self-repairing efficiency of tensile strength can reach 97.75% under 75 °C for 4 hours. |
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