Synthesis And Properties Studies On Polyimide Containing Natural Asymmetric Structure And Trifluoromethyl And Pyridine Ring Structure

Polyimides were synthesized by conventional aromatic diamines and aromatic dianhydrides,which are widely used in the field of manned spacecraft,automotive microelectronics,crude oil chemical mining and other fields,because these polyimides not only have excellent heat resistance and corrosion resistance,but also have good mechanical properties.However,in the wake of the rapid development of China's science and technology,during in the field of modern high-tech information science and technology,the polyimide prepared from the original aromatic to semi-aromatic,semi-aliphatic group and aliphatic group,through the improvement of preparation methods and the diversification of raw materials,these develop make imide products tends to be functionally diverse.The flexible screens mainly refer to flexible OLEDs,the success of flexible panels shoud contribution to the rapid development of high-end smartphones.Due to the low power consumption of flexible screens,good flexibility and foldability,which is important for the development of future wearable portable devices.PCB boards working in the high-frequency,high-radiation environments,may lead to many problems,such as lack of signal transmission and dielectric loss heating,which have plagued us and the slow spread of flexible portable wearable devices,so the development of high-performance functionalized polyimide materials such as low dielectric constant,low dielectric loss,high transparency and colorlessness is particularly important.Polyimide is a widely used material in microelectronics,therefore,scientists all over the world are working hard to research and develop new polyimide materials with low dielectric constant,low dielectric loss and high transparency.Therefore,in order to obtain a highly transparent colorless and low dielectric loss,low dielectric constant polyimide material,it is necessary to reduce the CTC charge transfer effect.To this end,we have designed a benzyl group containing an asymmetric structure from the natural product vanillin,and introduced a trifluoromethyl,pyridine ring structure into the polyimide to optimize the performance of the polyimide,mainly from the following two aspects to conduct research:First,using vanillin as the initial starting material,a novel new diamine,containning an asymmetric benzyl structure was successfully synthesised by reduction with potassium borohydride,nucleophilic substitution,and reduction of palladium on carbon and hydrazine hydrate,2-methoxy-1-(4?-aminophenoxy)-4-((4?-aminophenoxy)methyl)benzene(MAAMB)monomer.Through the preparation of the novel diamine MAAMB,a commercial asymmetric diamine 1,4,4?-APB was chosen to comparatively study the structure-properties relationship of MAAMB-derived polyimides which were condensed with the four wholly aromatic dianhydrides,6FDA,ODPA,BTDA,BPDA to prepare two kinds of polyimide films with natural asymmetry and structural symmetry,and named the asymmetric API1-API4 and the symmetrical SPI1-SPI4,repectively.Then,we measured systematic surface properties,mechanical properties,optical properties,and thermodynamic performance tests on the two symmetric and asymmetric series of polyimides.In the analysis of the thermal properties and mechanical properties of the polyimide film,we measured the glass transition temperature Tgs of the symmetric structure API series and the symmetrical structure SPI series in the rage of 241-262 ? and 245-308 ?,respectively.The tensile strengths are 82.2-92.7 MPa and 88.1-101.5 MPa,and the elongationat break is 4.8%-7.3% and 6.1%-10.1%,respectively.The 5% thermal weightloss temperature Td5 of the polyimide film in a nitrogen atmosphere was 448-478 ? and 507-521 ?,respectively;the 10% thermogravimetric temperature Td10 was 487-532 ? and 535-560 ?,respectively.This shows that the introduction of the benzyl into main chain would add the irregularity to the backbone structure and effectively improve the resulting PI's processability like solubility,optical performance while retaining thermal stability and mechanical properties,and the hydrophobicity is also improved.Second,using the terephthalic acid as raw material,terephthalaldehyde and trifluoromethyltrimethylsilane are reacted in DMF,potassium carbonate as a catalyst and DMF as a reaction solvent to synthesis p-(trifluoromethyltrimethylsilyloxy)diphenylmethane(PTTDM),followed by acidification with hydrochloric acid to remove TMS to prepare p-phenylene(trifluoro)methylbenzyl alcohol)(PTTBA),and then using the prepared diol to react with pchloronitrobenzene to prepare,p-bis(1-(5-nitrate)bis-2-pyridyloxy)-1-trifluoromethyl(PNPyTB),finally reduced with palladium on carbon and hydrazine hydrate to prepare p-bis(1-(5-amino-2)-pyridyloxy)-1-trifluoromethyl)benzene(PAPyTB).PAPyTB is carried at a molar ratio of 0%,20%,30%,40%,50%,60% with 4,4'-diaminodiphenyl ether(ODA),and then used the mixed diamines were copolymerization with 4,4-hexafluoroisopropyl phthalic anhydride(6FDA),4,4'-oxydiphthalic anhydride(ODPA),3,3',4,4'-benzophenone tetraacid Anhydride(BTDA),3,3'4,4'-biphenyltetracarboxylic dianhydride(BPDA)to prepare polyimide film,respectively.The performance of the synthesised polyimide films were characterized by us.The results revealed that the solubility of the prepared polyimide film were obviously improved with the increase of the molar ratio of PAPyTB,even in some low boiling solvents,for example,tetrahydrofuran(THF),chloroform(CHCl3)also has a good solubility;in some high boiling polar protic solvents such as N,N-dimethylformamide(DMF),N,Ndimethylacetamide(DMAc),N-Methylpyrrolidone(NMP)is dissolve completely.For the OPI-x series,the UV cutoff wavelength of the thin films were in the range of 331-388 nm,and the T550 transmittance is within the range of 59.3-84.8%.We used the wideangle diffraction XRD to test the molecular chain spacing ? in the range of 4.54-5.46.It was calculated by the Bragg equation that as the PAPyTB ratio increased,the molecular chain spacing increased and the solubility improve.Because the mixture of two diamines and one kind of dianhydride could cause cross-linking occurs between the molecular chains,therefore,when PAPyTB is doped with co-mixed diamine and dianhydride,PI performance may have fluctuate slightly,but it still maintains its thermodynamics and improves comprehensive performance of materials.