Preparation And Functionalization Of Polyimide With Low Thermal Expansion Coefficient

At present,the commercialized low thermal expansion coefficient polyimide materials are generally rigid and difficult to process,and are limited in the application of packaging materials,composite materials and microelectronic films for weapons.The main purpose of this paper was to ensure the low thermal expansion coefficient of biphenyl polyimide and simultaneously improve its processability,thermal stability and flexibility.Thus,the synthesis and functionalization of low thermal expansion coefficient polyimides from the point of molecular design have been studied on this thesis,and the physical and chemical properties of copolyimides prepared by copolymerization,siloxane modification and hyperbranched modification have been also discussed.Moreover,the functionalization of low thermal expansion coefficient polyimides by ZnO-Fe2O3-NiO and ZnO-Fe2O3-CeO2 has been performed through ion exchange method.It was expected that the polyimide composites could acted as photocatalyst,photothermalcatalyst and microwave induced catalyst to degra de pollution in waste liquid.In chapter 1,a series of copolyimides were prepared by copolymerization from 3,3’,4,4’-biphenyltetracarboxylic dianhydride(s-BPDA),2,3’,3,4’-biphenyltetracarboxylic dianhydride(a-BPDA),pyromellitic dianhydride(PMDA),p-phenylenediamine(PDA)and 4,4’-oxydialinine(4,4’-ODA).The crystallization characteristics,thermal properties,mechanical properties and surface morphology of the obtained polymers were discussed.The several properties of obtained polymers confirmed that the copolymerization of s-BPDA/PDA with a small number of 4,4’-ODA,a-BPDA and PMDA could enhance the film flexibility of s-BPDA/PDA without sacrificing its intrinsic ultra-low CTE characteristics.Two kinds of copolyimides with low thermal expansion coefficient were obtained.One of the copolyimides had low CTE(13 ppm.K-1),excellent tensile strength(182MPa),great elongation at break(22.8%),and high thermal stability(T5=602℃,T10=627℃).Another of the copolyimides had also low CTE(11 ppm·K-1),good tensile strength(142MPa),great elongation at break(26.2%),and high thermal stability(T5=583℃,T10=611℃).In chapter 2,to resolve the problem of difficult machining caused by poor solubility of polyimide in the first part,two kinds of diamine monomers containing borosiloxane have been prepared to increase solubility and hydrophobicity of copolyimide.Subsequently,the diamines have been reacted with s-BPDA,a-BPDA,PDA and ODA to synthesize borosiloxane-containing copolyimides with borosiloxane in the main chain and in the side chain.The relevant structure characteristics,molecular weight,melting properties,thermal properties,mechanical properties,surface morphology and hydrophobic properties have been investigated.It has been discovered that,the synthesized borosiloxane-containing copolyimides exhibited better solubility than borosiloxane-free copolyimides,and showed high glass transition temperatures(320-360℃),excellent thermal stability(570-620℃ for T10),great elongation at break(10%-14%)and low coefficient of thermal expansion(14-24 ppm·K-1).And the contact angles of copolyimides increased from 72° for neat copolyimide,to 96° for 5%of borosiloxane in the main chain of copolymer up to 107° for 10%of borosiloxane in the side chain of copolymer.In chapter 3,to ensure the high molecular weight copolyimides having low viscosity and excellent performance,a triamine has been prepared to be favor to hyperbranched copolymerization.Subsequently,the triamine has been reacted with s-BPDA,a-BPDA,PDA and ODA to synthesize a series of hyperbranched copolyimides.The relevant structure characteristics,molecular weight,melting properties,thermal properties,mechanical properties,surface morphology and hydrophobic properties have been investigated.It has been discovered that,the synthesized hyperbranched copolyimides exhibited excellent solubility and low viscosity.And their thermal stability,glass transition temperature and mechanical properties were not significantly reduced.The thermal expansion coefficient of the obtained polymer was 19-26 ppm·K-1,Tg was 311-324℃,T5 was 527-583℃,T10 was 553-602℃,the maximum elongation at break was 9.6-10.8%,and tensile strength was 148-157Mpa.And the contact angles of copolyimides increased from 72° for linear copolyimide,to76° for3%hyperbranched segments in the main chain of copolymer up to 85° for5%of hyperbranched segments in the main chain of copolymer.In chapter 4,a series of NiO-Fe2O3-ZnO layers on double surfaces of polyimide(PI)film have been fabricated by alkaline-induced chemical modification and ion-exchange reaction.The XRD,XPS and FT-IR analyses confirmed the successful formation of the heterostructured NiO-Fe2O3-ZnO layers on PI surfaces.The SEM and AFM showed that the NiO-Fe2O3-ZnO nanoparticles were dispersed uniformly on the PI surface and exhibited interesting mesh-shaped morphology.The UV-vis absorption results demonstrated that the PI/heterostructured NiO-Fe2O3-ZnO nanocomposite exhibited wide visible-light photo absorption in 400-740nm range.Moreover,the PI/heterostructured NiO-Fe2O3-ZnO nanocomposite films possessed excellent mechanical properties and acceptable adhesion,and they exhibited superior photocatalytic activity compared with PI/ZnO nanocomposite film toward the degradation of dyes under solar irradiation.The degradation rate of methyl orange over PZNF-3 after 240 min simulated solar light irradiation reached optimum value 96.2%.The improved photocatalytic activity of the PI/heterostructured NiO-Fe2O3-ZnO could be mainly attributed to the efficient separation of photoinduced electrons and holes of the photocatalysts,caused by the vectorial transfer of electrons and holes among ZnO,NiO and Fe2O3.In chapter 5,a series of CeO2-Fe2O3-ZnO mixed oxides layers on double surfaces of polyimide film have been fabricated by direct ion exchange technique.The obtained products were thoroughly characterized by various techniques including XRD,XPS,FT-IR,SEM,UV-VIS absorption spectra and TG.The results confirmed that the CeO2-Fe2O3-ZnO mixed oxides were successful formed and dispersed uniformly on surfaces of polyimide film.The PI/CeO2-Fe2O3-ZnO films displayed a wide visible-light absorption in the range of 400-710 nm.The initial decomposition temperatures of PI/CeO2-Fe2O3-ZnO films were all larger than 550℃.Moreover,the PI/CeO2-Fe2O3-ZnO films possessed outstanding photothermocatalytic and microwave catalytic activity compared with PI/FZnO nanocomposite film.The removal efficiency of methyl orange with the PIZNNIFE-3 film under UV-VIS-80℃-H2O2condition and microwave(MW)-H2O2 condition in 12.0 min reached respectively up to 92.7%and 98.7%.In conclusion,a series of low thermal expansion coefficient polyimides have been successfully designed and synthesized in this thesis.The polymers not only kept the excellent physical and chemical properties of the polyimides,but also had the unique properties of polyimide with low thermal expansion coefficient through reasonable structure design,which provided a new type of polyimide with low thermal expansion coefficient.Moreover,the catalytic nanocomposites with good overall performance were introduced based on low CTE polyimides through their functionalization.