Study On Synthesis And Properties Of DETDA Polyimide Containing Heterogeneous Mixture Diamine

Polyimide(PI)is a kind of material with excellent comprehensive properties.It is widely used in engineering plastics,electronic devices and so on.How to solve the problem of PI processing is always the focus of PI research.Diethyltoluidine(DETDA)is an isomeric mixture diamine monomer,which was born in the 1980s and is an important chemical additive.Because the monomer is a 5-substituted monocyclic aromatic diamine,the amino group is encapsulated by the surrounding methyl ethyl group,resulting in a large steric hindrance effect and a small diamine reaction activity.The PI molecular weight synthesized from DETDA as diamine monomer is small and difficult to form film.So far only used as polyurethane chain extender and other additives,the output is very large,but the use is relatively single.In this paper,the method and conditions for the synthesis of PI with DETDA as the diamine monomer are studied.Using melt polymerization method,using benzoic acid as solvent,and dianhydride monomer 4,4'-oxydiphthalic anhydride(ODPA),3,3',4,4'-biphenyl tetracarboxylic dianhydride(BPDA),3,3',4,4'-benzophenone tetracarboxylic dianhydride(BTDA),2,3',3,4'-biphenyl tetracarboxylic dianhydride(?-BPDA),and4,4'-(4,4'-isopropylidene-diphenoxy)-bis-(phthalic anhydride)(BPADA)are reacted to produce a series of PI molding powder.The reaction temperature was 155?and the reaction time was 2 h.The results show that,the dissolving property of the molding powder is better,PI films can be obtained by dissolving and reprocessing into films.But PI film has a general film formation,the mechanical properties are poor.Afterwards,through the method of copolymerization modification and orthogonal experiment,two kinds of ternary copolymerized PI,ether-ketone anhydride type PI and ether-biphenyl type PI were synthesized by orthogonal experiment,and the best solubility performance and reaction conditions was obtained.The two series of PI molding powders have better film-forming properties and better thermal properties.The mechanical properties of the prepared PI film have been enhanced and the performance is better.At the same time,it was discovered that aftermixingDETDAwiththeflexiblediaminemonomer1,3-bis-(4'-aminophenoxy)-benzene(BAPB),it can be prepared with ODPA at room temperature by solution polymerization to prepare a PAA solution.The PI film can be obtained by thermal imine.The glass transition temperature of the PI film is about 230?,the optical transmittance is good,the transmittance at 500 nm wavelength is greater than80%,and the mechanical properties are average.For further improvement of mechanical properties of PI films,Preparation of PI/nano Si O₂composite films,Thermal and mechanical properties have been improved.The prepared polymers were characterized by Fourier transform infrared spectrometer(FT-IR),thermogravimetric analyzer,UV-Vis spectrophotometer and other testing instruments,and the following conclusions were obtained:(1)Preparation conditions of ether-ketone anhydride type PI molding powder with optimum solubility are as follows:The reaction temperature was 155?,the amount of benzoic acid in solvent was 12.2121 g(1:50),the reaction time was 2.5 h,and the ratio of dianhydride was 8:2(ODPA:BTDA);The preparation conditions of ether-diphenyl anhydride type PI molding powder with optimum solubility are as follows:The reaction temperature was 150?,the amount of benzoic acid in solvent was 12.2121 g(1:50),the reaction time was 1.5 h,and the ratio of dianhydride was 8:2(ODPA:BPDA);Ether-ether anhydride type PI film with optimum thermal expansion coefficient is prepared at room temperature,magnetic stirring,the solid content is 15%,reaction time is 12 h,the ratio of DETDA to BAPB is 2:8.(2)The PI synthesized with DETDA as diamine monomer has excellent thermal properties in a nitrogen atmosphere,the initial decomposition temperature is more than500?,the maximum decomposition rate is 511?574.7?,and the residual rate of 800 is50%and 60%respectively.(3)The optical transmittance of PI films synthesized from DETDA as diamine monomer is better,with a maximum transmittance of 90%and a transmittance of 82.49%at500 nm.(4)The fluorescence performance of PI synthesized with DETDA as diamine monomer is almost the same.When the emission wavelength is 600 nm,multiple excitation peaks appear in the obtained excitation spectrum,among which the stronger ones are 480nm and 530 nm.When the emission wavelength is 480 nm,multiple emission peaks appear in the obtained emission spectrum,among which the stronger ones are 540 nm and 600 nm.(5)PI molding powder synthesized with DETDA as diamine monomer has good solubility,soluble in several common solvents,insoluble in acetone,and has good processing property.(6)In the PI/SiO₂ composite films prepared with DETDA as diamine monomer,the dispersion of in-situ dispersion method is better than that of mixed method,and the performance is improved significantly.