Preparation And Properties Of Self-healing Poly (Urethane-Urea) Elastomer Based On Dynamic Disulfide Bonds

The polyurethane elastomers with designable structure and adjustable properties contain many polar groups such as hydroxyl,amino,ester,urethane and urea groups,which makes the polyurethane elastomers have a large number of hydrogen bonds.Therefore,polyurethane elastomers are very suitable for the field of self-healing polymer materials.In many intrinsic self-healing polyurethane elastomers,researchers have paid more and more attention to the method of introducing dynamic disulfide bonds because of the mild exchange reaction conditions and the ability to respond to multiple stimuli.Although self-healing polyurethane elastomers based on aromatic disulfide bonds can rapidly self-healing at room temperature,the introduction of aromatic groups usually leads to yellowing,poor transparency and low mechanical strength of polyurethane elastomers.Therefore,self-healing polyurethane elastomers based on aliphatic disulfide bonds are expected to be the solution to the problem that polyurethane elastomers have good mechanical properties and high self-healing efficiency.At present,most of the literatures about self-healing polyurethane elastomers based on aliphatic disulfide bonds are directly used with 2-hydroxyethyl disulfide(HEDS)or cystamine(CY)as chain extender.Although these related researches have achieved good results,HEDS or CY as raw materials containing disulfide bonds also have the problems of high price and difficulty to batch prepare self-healing polyurethane elastomers.Based on this,in this paper,cystine dimethyl ester(CDE)was prepared by esterification reaction from cystine,which was widely used and cheap.Then,aliphatic CDE was used as chain extender to prepare self-healing poly(urethane-urea)(PUU)elastomers based on dynamic disulfide bonds.Then,PCL,PTMG and PPG were used as soft segments to prepare various self-healing PUU elastomers.The effects of various factors on the mechanical properties and self-healing properties of PUU elastomer were studied from the perspective of structure.The optimum formula of PUU elastomer with high mechanical properties and high self-healing efficiency was explored,and the regulatory relationship between the structure and properties of PUU elastomer was obtained.The main conclusions are as follows:(1)Synthesis of CDE and study on self-healing PUU elastomer with high performances:CDE was synthesized from cystine by esterification.PCL-based self-healing PUU elastomer with high performance showed excellent mechanical properties and self-healing properties:the tensile strength and elongation at break of the original samples reached 27.1 MPa and397.7%respectively;after being healed at 60?for 24 hour,?_?and?_?reached 95.3%and93.5%respectively,which was due to synergistic effect of dynamic disulfide bonds exchange reaction and reversible hydrogen bonds.Due to its high degree of microphase separation,PTMG-based self-healing PUU elastomer with high-performances exhibited good mechanical properties,with tensile strength and elongation at break of 13.6 MPa and 531.3%,respectively;after being healed at 80?for 24 hour,?_?and?_?are 97.1%and 90.3%,respectively.The PPG-based self-healing PUU elastomer with high-performances was amorphous structure with a low degree of microphase separation.The tensile strength and elongation at break were 3.64 MPa and 416.7%,respectively;after being healed at 60?for24 hours,?_?and?_?are 89.8%and 89.3%.(2)Study on PCL-based self-healing PUU elastomer system:(1)In the PCL1k-IPDI system,the tensile strengths of OPU,APU,CPU and SPU were successively 1.92 MPa,46.3MPa,41.6 MPa and 27.1 MPa,which was due to the different degrees of microphase separation(OPU<SPU<CPU<APU).The self-healing ability of the four elastomers was:OPU?SPU>CPU>APU.The stress relaxation activation energies of OPU and SPU were 97.5k J/mol and 191.9 k J/mol,respectively.(2)In the PCL1k-CDE system,the degree of microphaseseparationofthefourelastomerswas:CL-H-SPU>CL-HM-SPU>CL-IP-SPU>CL-M-SPU;after being healed at 60?for 24 hours.Theself-healingefficienciesofthefourelastomerswas:CL-IP-SPU>CL-HM-SPU>CL-M-SPU>CL-H-SPU.(3)In the PCL-IPDI-CDE system,when the hard segment content exceeded 35%,the sample had an amorphous structure;the strength and toughness of PCL3k-3 were well balanced:tensile strength and elongation at break reached 41.5 MPa and 472.9%,respectively.After being healed at 60?for 24h,when the soft segment was PCL1k or PCL3k,the self-healing efficiency of PUU with low hard segment content was the highest.(4)Increasing the temperature and extending the healing time both can promote the improvement of self-healing efficiency,and the former had a more obvious effect on the improvement of self-healing efficiency than the latter.(3)Study on PTMG-based self-healing PUU elastomer system:(1)In the PTMG1k-IPDI system,the tensile strengths of OPU,APU,CPU,and SPU were successively0.71 MPa,50.2 MPa,44.6 MPa and 13.6 MPa,which were due to the different degrees of microphase separation(OPU<SPU<CPU?APU).The self-healing ability of the four elastomers was:APU<CPU<OPU<SPU,and the stress relaxation activation energies of OPU and SPU were 134.3 k J/mol and 104.8k J/mol,respectively.(2)In the PTMG1k-CDE system,the degree of microphase separation of the four elastomers was:T-HM-SPU>T-IP-SPU>TM-SPU>TH-SPU.After being healed at 80?for 24 hours,the self-healingefficiencyofthefourelastomerswas:T-IP-SPU>T-HM-SPU>T-M-SPU?T-H-SPU.(3)In the system of PTMG-IPDI-CDE,when the molecular weight of PTMG was 1000,the tensile strength and modulus of the elastomer increased with the increase of the hard segment content,and the elongation at break declined with the increase of the hard segment content.When the molecular weight of PTMG was2000 or 3000,the sample was too soft to complete the mechanical test.After being healed at60°C for 24 hours,the?_?and?_?of PTMG1k-1 reached the maximum values(80.2%and89.4%).(4)Study on PPG-based self-healing PUU elastomer system:(1)In the PPG1k-IPDI system,the tensile strength of APU,CPU and SPU were 32.9 MPa,14.7 MPa and 3.64 MPa,respectively,which was attributed to the different degree of microphase separation(SPU<CPU?APU).The self-healing ability of the three elastomers was:APU<CPU<SPU,and the stress relaxation activation energy of SPU was 109.9 k J/mol.(2)In the PPG1k-CDE system,the degree of microphase separation of the four elastomers was:P-H-SPU>P-HM-SPU>P-IP-SPU>P-M-SPU.After being healed at 60?for 24 hours,the self-healingefficiencyofthefourelastomerswas:P-IP-SPU>P-M-SPU>P-HM-SPU?P-H-SPU.(3)In the PPG-IPDI-CDE system,when the PPG had the same molecular weight,the tensile strength and modulus of the elastomer increased with the increase of the hard segment content.The tensile strength of the three elastomers corresponding to the soft segment of PPG2k were all above 10 MPa,and the elongation at break were all exceeding 500%.The PUU prepared with PPG3k as the soft segment was too soft to test the mechanical properties at room temperature.The self-healing efficiencies of the three elastomers corresponding to PPG1k all decreased with the increase of the hard segment content.The values of?_?of the three elastomers corresponding to PPG2k were about 50%,while the values of?_?all exceeded 85%.