Preparation And Performance Study Of Shape Memory Polymer Based On Different Crosslinking Ways

Shape memory polymers are smart materials that will become the mainstay of smart materials in the future.However,they often face difficulties in industrialisation,poor mechanical properties,single temporary shape,the need for external forces and non-recyclability.By designing the crosslinking of polymers,such as covalent,ionic,and dynamic covalent bonding,the crosslinking network will enable the polymer to perform different functions and solve these challenges.Therefore,this study focuses on the crosslinking of shape memory polymers.Three different crosslinking methods were prepared and tested for crosslinking density,crystallinity,phase structure and shape memory properties to investigate the influence of the crosslinking methods on the macroscopic properties.Detail studies have included:(1)Triple shape memory polymer based on covalent cross-linked trans-polyisoprene/poly(ethylene-co-vinyl acetate)(TPI/EVA)polymer composites.Due to the large number of double bonds in TPI and the active hydrogen in the ester group of the EVA,diisopropyl peroxide(DCP)is used to initiate the reaction,resulting in the formation of TPI-g-EVA at the phase interface.With the different crystalline properties of TPI and EVA and the grafting reaction initiated by DCP,The TPI/EVA polymer composites were prepared by mechanical compounding and vulcanization at high temperature and pressure.The effects of the TPI/EVA ratio and DCP contents on the vulcanization parameters,crystallization properties,mechanical properties and triple shape memory properties of the polymers were investigated in detail.The results showed that the triple shape memory behaviour of the TPI/EVA polymer composites was verified by DMA,with the first temporary shape fixation increasing with an increasing EVA mass ratio and the second temporary shape fixation rate being the lowest at 97.1%,showing a good triple shape memory function.The phase interface of TPI/EVA polymer composites was verified using SEM,As the EVA mass ratio increased,the two-phase interface changed from smooth to rough,and when the EVA mass ratio exceeded 40%,the tendency for separation of the two phases increased and the tensile strength decreased to 14.4 MPa.By using DCP as a compatibilizer,the graft copolymer TPI-g-EVA was found to be formed by DCP-induced free radical reaction.The polymers exhibited a smooth structure at high DCP content.The Tc and Tm of the TPI/EVA polymer composites gradually decreased as the DCP content increased.(2)Triple shape memory polymer based on covalent and ionic cross-linking of trans-polyisoprene/paraffin(TPI/P)polymer composites.To utilize the difference in crystallization properties between TPI and P,zinc methacrylate(ZDMA)was used as a cross-linking agent to achieve ionic cross-linking,which in turn increased the crystallization difference and gave the polymer composites the triple shape memory function,and DCP was introduced as a covalent cross-link agent,so that the polymer composites possessed a dual cross-linked network of ionic and covalent cross-linking.The TPI/P polymer composites were characterised using vulcanization characteristic curves,a universal testing machine,XRD,DSC and DMA to investigate the relationship between the crosslinking network and macroscopic properties of the polymer composites with ZDMA as a variable.The results showed that the TPI/P polymer composites were ionic crosslinked by the introduction of ZDMA,the addition of ZDMA increased the overall crosslinking density,the ionic crosslinking disrupted the crystallinity of TPI phase.The crystallinity of the TPI phase in the polymer composites were increased when the ZDMA contents was at 2 parts,this ensured that the difference between the melting temperatures of TPI and paraffin was around 10℃,thus making the TPI/P composites had triple shape memory function.By varying the variables of ZDMA and determining the sample mechanics,shape memory recovery rate,and other comprehensive properties for each gradient experiment,it was determined that when ZDMA was added at 2 phr,it neither over-cross-linked nor destroyed the crystalline region of the dulcimer,but also improved sufficient elastic recovery for the triple shape memory polymer and achieved a reinforcing effect on the TPI/P polymer composites.(3)Two-way shape memory polyurethane based on dynamic covalent and hydrogen bonding crosslinked.A series of two-way shape memory polyurethanes(DPU)were designed and synthesised due to the repetitive processing and shape reconfiguration characteristics of dynamic thiocarbamates and quadruple hydrogen bonds.The polymers(DH-PU)cross-linked by dynamic thiocarbamate and quadruple hydrogen bonding were obtained by introducing different levels of UPy into the DBU.The effects of the two cross-linking methods on their macroscopic properties were investigated by controlling the R-value and UPy content.It was found that adjusting the R value resulted in a modulation of the crystalline properties and the switching temperature.When the R value was increased from 1.05 to 1.65,the crystallisation temperature decreased from-10.0℃ to-13.3℃and the melting temperature decreased from 34.1℃ to 31.2℃.Due to the introduction of dynamic covalent bonding,the material showed only a 6%decrease in tensile strength and 332.4%elongation at break after three repetitions of processing.The DMA tested showed a maximum reversible strain of 8.94%at 37℃ recovery.The successful synthesis of UPy was demonstrated by NMR,13C NMR and FT-IR.The DMA results showed that the average reversible strain of the sample decreased from 16.3%to 3.3%when the UPy content was increased from 0%to 6%;furthermore,by controlling the programming step of DH-PU,the DMA results demonstrated the presence of a quadruple hydrogen bonding network in the sample,while verified that the addition of UPy gave DH-PU a special triple shape memory behaviour.