Study On The Preparation And Properties Of Self-healing Polyurethane Materials Based On Disulfide Bonds

Polymer materials are widely applied in the field of engineering.The damage and aging problems of materials are inevitable in the service process.The damaged sites of self-healing materials can be repaired by themselves,extending their service lives and reducing costs.It is of important significance to endow polymer materials with self-healing function.Polyurethane（PU）is a kind of polymer material with excellent properties.Self-healing PU based on disulfide bond has been widely focused for the relatively low temperature and high efficiency of self-healing process.For the traditional preparations of self-healing PU,the dinols containing disulfide bonds were used as chain extenders,in which disulfide bonds were introduced into the hard segment phases and their the dynamic exchange is hindered.In this work,the preparation method of self-healing PU was modified.2,2’-Dithiodiethanol（DTDE）was pre-fixed in two polyether glycol molecular chains,and the disulfide bonds were introduced into the soft segment phase.The self-healing efficiency of the self-healing PU is improved with the help of the strong movement ability of the soft segment chains.The self-healing PU system was systematacially and deeply studied.The main contents and results are as follows:（1）Polytetramethylene ether glycol1000（PTMG1000）and isophorone diisocyanate（IPDI）were used as the main raw materials,and a series of self-healing PUs were prepared.The effects of curing parameter,crosslink density,graphene content and hard segment content on the self-healing performance of PUs were further studied in this work.The results show that the introduction of crosslinking agent and graphene will reduce the self-healing efficiencies of PUs.When the curing parameter is 1.11,self-healing PU with hard segment content of 35%has the optimal performance.The tensile strength（σ）and the elongation at break（ε）at room temperature can reach 1.93 MPa and 1364%,respectively.After heated at 80℃ for 12hours,the self-healing efficiencies of its tensile strength（R_σ）and elongation at break（R_ε）can reach 90.85%and 59.87%,respectively.Dynamic thermomechanical analysis and Arrhenius equation analysis on the activation energy of polymer chain motion show that,the stronger mobility of polymer chains,the higher self-healing performance of PUs.（2）By introducing dimethoxydiphenylsilane（DMDPS）,PTMG2000 and IPDI were used as the main raw materials,and a series of self-healing PUs were prepared.Energy dispersive spectroscopy analysis show that the disulfide bonds and diphenyl silicon groups of PUs prepared by the modified method are mainly involved in their soft phases,while those of PU by the traditional method in the hard phase.Although the mechanical properties of PUs have been weakened by the disulfide bonds involved in soft phases,whose self-healing efficiencies are greatly improved by the synergistic effect of diphenyl silicon groups-increasing the distance between polymer chains,enhancing the mobility of polymer chains,and promoting the migration of sulfur-containing groups to the damaged sites.The analysis of activation energy for the movement of polymer chains based on dynamic mechanical thermal analysis and Arrhenius equation also shows that,the bigger contents of disulfide bonds and diphenyl silicon groups,the higher self-healing performance of PUs.When the molar ratio of DMDPS to DTDE is 1/2,the comprehensive performance of the prepared self-healing PU（S2）is the best.Theσand theεat room temperature can reach 3.29MPa and 779%,respectively.After heated at 80℃ for 12 hours,the R_σand R_εcan reach 97.53%and 81.54%,respectively.The healing process of self-healing PU is composed of the dynamic exchange of disulfide bonds and the interpenetration and intertwining of polymer chains,in which the former can be completed in a shorter time,while the latter at damaged sites in a longer time.This process is dynamic and has temperature and time dependencies.（3）By adopting the optimal preparing technology of S2,three types of self-healing PUs were respectively prepared based on polycaprolactone diol（PCL）,polypropylene glycol（PPG）and PTMG,named as S_PCL,S_PPGand S_PTMG.It shows that the mechanical properties of S_PCLare superior to S_PPGand S_PTMGdue to the strong crystallization of PCL segments.However,due to the limitation of cohesive energy,S_PCLhas poor molecular mobility,as well as self-healing performance.The tests suggest that S_PTMGand S_PPGboth have excellent comprehensive performance.The effects of curing parameter,polyol molecular weight and hard segment content on the self-healing performance of S_PTMGand S_PPGwere further studied.Dynamic thermomechanical analysis and Arrhenius equation analysis on the activation energy of polymer chain motion show that,the stronger mobility of polymer chains for S_PPG,the higher self-healing performance for it.When the curing parameter is 1.20 and polyol molecular weight is 2000,S_PTMGand S_PPGwith hard segment content of 35%both have excellent self-healing performance.After heated at 80℃ for 12 hours,the R_σof S_PTMGand S_PPGcan reach 97.97%and 98.63%,respectively.The R_εof S_PTMGand S_PPGcan reach 99.03%and 98.41%,respectively.