Regularly,Tunably Rigid-flexible Crosslinking Network And Shape Memory Properties

Along with science and technology advancement and economy progress,the material has been developing forward to high performance,environmental protection,and sustainable development.Among them,due to great shape memory properties and excellent mechanical and processing properties,the shape memory epoxy resin(shorted as SMEP)has become a hot research.First of all,high epoxy value of eugenol epoxy resin(shorted as EUEP)was synthesized by eugenoland catalyststhat is tetramethylammonium bromide(shorted as TMBA)/sodium hydroxide(NaOH).Then,the tunable rigid-flexible epoxy resins(shorted as TRFEPs)weresynthesized by ultraviolet(TV)light thiol-ene click chemistry.This UV light thiol-ene click chemistry possesses the features:simple,selective,efficient,and environmentallyfriendly.A series of regular epoxy resins with various chain lengths(DTAGEs)were also synthesized by ultraviolet(UV)light thiol-ene click chemistry using allyl glycidyl ether(AGE)as the raw material.The FTIR and ’H NMR spectraindicated that TRFEPs and DTAGEs succeed in being synthesized.Next,a series of regular and tunable rigid-flexible crosslinking networks,TRFEPs/4,4’-diaminodiphenylmethane(DDM),and an irregular crosslinking network,have been prepared by using DDM as curing agent to investigate the effects of regularity and flexiblity on shape memory properties.The thermal,dynamic thermo-mechanical properties were characterized by DSC,DMA.Mechanical properties were charactized by tensile test.Finally,shape memory properties of all regular crosslinking networks were tested by tensile mode of DMA.Conclusion are as follows.Firstly,with the flexibility of the crosslinking networksincreasing,glass-transition temperature(Ta),storage modulus(E’)at 25℃,and tensile stressdecrease and elongation at break increase;secondly,the tunable rigid-flexible crosslinking networks show a plastic materialfracture feature that is yielding phenomenon and had relatively high tensile strength(20-44 MPa);thirdly,the regular crosslinking networks exhibited excellent shape memory performance with high shape memory fixity(>97%)and shape memory recovery(>99%),while the irregular crosslinking network has relatively more degradation of shape memory properties;fourthly,the regularity of network was the primary effect factor on the shape recovery speed.Finally,another regular crosslinking networks DTAGEs/DDM and a corresponding irregular crosslinking network were prepared.Compared to the crosslinking network TRFEP/DDM,the rigidity of DTAGEs/DDM is decreased.The thermal,dynamic thermo-mechanical properties were characterized by DSC,DMA.Shape memory properties of all regular crosslinking networks were tested bytensile mode of DMA.Combined with the results of TRFEP/DDM shape memory properties,qualitative study is carried out by peak-differentiation-imitating method,which is used to investigate the effect of crosslinking network regularity and the effect of rigid segment,flexible segment on shape memory properties.Conclusions are as follows.Firstly,with the flexibility of the crosslinking networks increasing,Tg and E’(0℃)decrease.Secondly,the shape memory recovery is composed of the rigid segment recovery and the flexible segment recovery.Thirdly,crosslinking network regularity has a great influence onrigid segments recovery speed,while little influence on flexible segments recovery speed.For the two systems in thework,the effect of network regularity on therecovery speed is greater than thatof flexiblity.Fourthly,for the same system(TRFEP/DDM or DTAGE/DDM),the regularity of networkwas the primary effect factor and the flexibility was the subordinate effect factoron the shape recovery speed.For the regular crosslinking networks with similar flexible segments,the harder the crosslinking is,the faster the shape recovery speed is.