Preparation,Shape Memory And Tribological Properties Of Biphenyl Epoxy Resins

Shape memory materials(SMPs)is a kind of shape memory materials based on the conformational transformation of polymer segments.It can memorize the initial shape,fix the temporary shape and restore the initial shape through the movement and freezing of segments under external stimulation(heat,light,electricity,magnetism,solution,etc.).Due to the characteristics of high shape recovery rate,significant shape memory effect,fast stimulus response,corrosion resistance and easy processing,shape memory polymers can be widely used in biomedical,aerospace and other fields.As a traditional engineering material,epoxy resin(EPS)has good mechanical properties,chemical stability,electrical insulation properties and excellent adhesion with other materials,which can be widely used in coatings,adhesives,electronic appliances and other fields.Using the glass transition temperature of EP as the transition temperature and the crosslinking structure as the stationary phase,the SMP material can be designed and prepared.Traditional epoxy resin has high strength and poor toughness,so its application in many fields is limited.In order to prepare multifunctional and high toughness shape memory epoxy resin,the following work was carried out in this paper:(1)A series of shape memory biphenyl epoxy resins(BPEP)were prepared by UV curing method with diglycidyl biphenyl ether(DGEBP)as epoxy monomer and m-xylylene diamine(MXDA)as curing agent.The crosslinking density,transition temperature,microstructure and mechanical properties of BPEP can be controlled by adjusting the epoxy/amine molar ratio and post-treatment temperature.BPEP has good shape memory,and its shape fixation rate is more than 99%and shape recovery rate is more than 97%.Its wide transition temperature(T_r)can give it triple shape memory effect.It was found for the first time that the material post-treatment temperature had a significant effect on T_r.This is mainly due to the free movement of polymer segments at high temperature and the benzene ring structure between the segments?-?,as a new physical crosslinking point,the layered structure is formed by self-assembly,which can improve the crosslinking density.The structure and performance of BPEP can be easily adjusted by this performance.(2)Based on the experimental results in Chapter 2,it can be found that when the BPEP is deformed by thermal stimulation,the speed of shape recovery is relatively slow,which is not conducive to the recovery of local shape.Moreover,the addition content of photoinitiator(3wt%)is higher than that of peer research.Therefore,in order to reduce the content of photoinitiator and improve the shape recovery rate and response mode of the materials,a dual photoinitiator system was used to reduce the content of the main initiator.Iodonium salt cationic photoinitiator(IOD)was used as the main initiator,and aromatic ferrocene(FC)was used as the photosensitizer.Near-infrared(NIR)responsive biphenyl epoxy resin/graphene composites(BPEP/GR)were prepared by adding different amounts of graphene.BPEP/GR has a good shape memory property,with a shape fixation rate of over 99%and a shape recovery rate of96%.Because graphene has good photothermal conversion performance,the material has faster near-infrared photo-response than pure thermal response.The near-infrared light reprogramming of biphenyl can be realized by using the activation and reorganization of biphenyl crystal phase at high temperature.(3)Based on the results of the previous two chapters,the movement of BPEP segment at high temperature will make the biphenyl structure unit due to the change of temperature?-?,as a new physical cross-linking point,the layer structure formed by self-assembly can improve the cross-linking density and mechanical properties of BPEP,which is helpful to improve the tribological properties of BPEP.The tribological properties of BPEP were investigated,and the effects of different crosslinking density and different test temperature on the tribological properties were investigated.Because the biphenyl structural units will be aligned along the friction direction under the action of high temperature and external force,the friction coefficient will be kept low.At high temperature,the self-reinforcing effect of the material makes the BPEP segments more closely arranged and not easy to wear.The friction coefficient and wear rate of BPEP are lower than those of common polymer based lubricating materials during the transition from glassy state to rubberized state.This work provides a simple method for the preparation of BPEP self-lubricating film.The excellent tribological properties also broaden the application scope of BPEP,and promote the further development of shape memory polymer in the field of tribology.