Shape Memory Behavior Of Nylon 1212 Thermoplastic Polyamide Elastomer

Shape memory polymer(SMP)is a type of material that recovers from a programmed temporary shape to its original shape under the action of external stimuli(such as light,heat,magnetism,and electricity).As a class of stimuli-responsive polymers,SMP can sense the surrounding environment and produce a direct response.Shape memory behavior has been found in various polymers,including amorphous polymers,semi-crystalline polymers,and liquid crystal elastomers.SMP shape memory behavior is achieved by designing materials with two or more stages,one of which is responsible for fixing the original shape,and the other stage can model the desired temporary shape.Thermoplastic polyamide elastomer(TPAE)is an(AB)n-type block copolymer formed by condensation polymerization of polyamide hard segment and polyester or polyether soft segment.It has many excellent characteristics,such as the structure can be designed,can be formed into microphase separation structure,good thermal stability,flexibility and elasticity.Therefore,different soft and hard segment materials in TPAE can be designed in order to obtain shape memory thermoplastic polyamide elastomer with excellent performance.Compared with other shape memory materials,thermoplastic elastomers have a wider shape memory recovery temperature range,better biocompatibility and better processing ability.In recent years,domestic and foreign research scholars have developed a strong interest in it.In this paper,PA1212 prepolymers with different molecular weights are synthesized by two-step melt polymerization with dodecanedioic acid as the end capping agent.Two types of thermoplastic polyamide elastomers are synthesized through PA1212 prepolymer and soft segments of different types and molecular weights.One type is a series of thermoplastic polyamide elastomers(poly(ether glycol-b-amide),PEGBA)synthesized by the polyesterification reaction with polyether glycol,and the other type is a series of thermoplastic polyamide elastomers(poly(ether amine-b-amide),PEABA)synthesized by the polyamide reaction with polyether diamine.The main conclusions of the work can be summarized as:(1)The structure of the copolymer is characterized by FT-IR and ~1H-NMR,indicating the successful synthesis of the copolymer.The DSC test results show that the melting and crystallization peaks of PEGBA and PEABA appear in the soft and hard segments in the heating and cooling curves,and the melting point and crystallization temperature of the copolymer are affected by the soft and hard segments.As the molecular weight of the hard segment increases,the melting point and crystallization temperature of the hard segment rise.When the molecular weight of the soft segment increases,the melting point and crystallization temperature of the soft segment increase.(2)XRD test results show that the copolymers all exhibit a triclinic?crystal phase similar to the hard segment PA1212.The greater the molecular weight of the hard segment,the more perfect the crystallization.When the chain length of the soft segment increases,the crystallization of the hard segment is restricted.The variable temperature XRD test shows that the Brill transition temperature of PEGBA increases with the increase of the molecular weight of the hard segment.The temperature-variable FTIR test shows that the molecular chain of the copolymer mainly forms intermolecular hydrogen bonds inside.(3)The AFM test shows that the copolymer exhibits a two-phase structure with microphase separation.TG test shows that the initial decomposition temperature of the copolymer is around 370?,and the maximum decomposition temperature is around430?.The results show that the synthesized thermoplastic polyamide elastomer has good thermal stability.It can meet the general processing requirements of polymers and will not be degraded under mild conditions.(4)The DMA results shows that PEGBA-11,PEGBA-12,PEGBA-21 and PEGBA-22 have shape memory behavior in the PEGBA copolymers.Among them,the PEGBA-12 sample showed excellent shape memory behavior at 20-50?,the shape memory fixation rate can reach 92%,and the recovery rate can reach 98%.In the PEABA series copolymer,PEABA-11,PEABA-12,and PEABA-22 have shape memory behavior.PEABA-11 sample shows shape memory behavior at 80?.PEABA-12 sample shows excellent shape memory performance at 40-70?,the shape memory fixation rate can reach 96%,and the recovery rate can reach 100%.PEABA-22 sample shows excellent shape memory performance at 50-70?,the shape memory fixation rate can reach 88%,and the recovery rate can reach 89%.