Synthesis And Dielectric Properties Of Metathesis Polymers With Azobenzene Pendants

High-performance dielectric materials have played great roles in the modern electronics and electrical power systems,such as polymer film capacitors and hybrid electric vehicles.Polymer dielectric materials are more suitable for these applications because they are inexpensive,possesing high dielectric strength,high energy density,and low dielectric loss.However,the low dielectric constant（2-6）of polymer dielectric materials limits its application in the field of energy storage.It is necessary to further increase the dielectric constant of polymer dielectric materials.In this thesis,by introducing strong push-pull azobenzene chromophores and triphenylamine group into the polymer side chain,all-polymer dielctric materials with high dielectric constant and high energy density were obtained.The main content was as follows:Homopolymer poly[N-4-（nitroazophenyl）-norbornene-pyrrolidine]（PFANP）and the block copolymer poly[N-4-（trifluoromethylazophenyl）-norbornene-pyrrolidine]-b-poly（N-4-（nitroazophenyl）-norbornene-pyrrolidine）]（PFANP-b-PNANP）were synthesized by ring-opening metathesis polymerization（ROMP）using the third Grubbs’catalyst（Ru-III）.The self-assembly behavior and morphology of the block copolymer were investigated by DLS and TEM,respectively.Due to the difference in solubility of the diblocks in THF,the copolymer could self-assemble into a core-shell nanostructure.The block copolymer PFANP₂₀₀-b-PNANP₁₀₀00 exhibited the dielectric constant of 19.1,the dielectric loss of 0.01-0.02,and the energy density of 5.54 J cm^-3at electric field of 240 MV m^-1.Additionally,the effect of photo-isomerization of azobenzene group on the dielectric properties of polymers was investigated,and the dielectric constant could be tuned by the trans-cis transition of azobenzene group.MonotriphenylaminenorbornenepyrrolidinemonomerTANPand di（triphenylamine）norbornenepyrrolidine monomer BTANP containing the polar substituents of both azobenzene and triphenylamine pendants were designed and prepared.The corresponding homopolymers PTANP and PBTANP were obtained by ROMP.The dielectric constant of PTANP was about 13.5,because the polymer side chain contains strong polar groups（azobenzene,ester group,and triphenylamine containing a strong electron withdrawing substituent）.The dielectric constant of PBTANP was further improved to 15.7,due to the presence of a di（triphenylamine）substituent.Besides,the dielectric loss of the polymer is relatively low（0.01-0.02）,and the storage density of PBTANP can reach 5.09 J cm^-3 at electric strength of 270MV m^-1.