Synthesis,Film Fabrication And Optoelectric Properties Of Sulfoxide Polyimides

Transparent polyimides,as a kind of heat-resistant speciality polymer,possess high application value in flexible display and biological medical fields.Typical aromatic transparent polyimides,which contain conjugate biphenyl structure unit,possess high heat resistance properties.However,strong charge transfer complex(CTC)always exists in intra/intermolecular chains,which brings strong visible light absorption and high yellow index(YI).Besides,it suffers from high birefringence and phase retardation caused by larger molecular orientation degree.As a result,the optical properties cannot meet the harsh requirements of flexible display applications.It is urgent to design transparent polyimide molecules with high rigidity,low molecular orientation and weak intermolecular charge transfer.For this purpose,this thesis have designed and synthesized a new type of rigid sulfoxide diamine monomer,which were copolymerized with aromatic dianhydride monomer to prepare halogen-free sulfoxide transparent polyimide,fluorate sulfoxide transparent polyimide and sulfoxide macrocyclic trimer.Optical properties,thermal properties,structure-function relationship and the engineering application of the novel polyimide were researched in detail.The rigidity,steric hindrance and electron-pull effect of sulphoxide structural unit were applied to ensure high heat resistance,and effectively improve the optical transmittance,as well as to reduce the yellow index,birefringence and phase retardation.This research provided a new strategy for the design of high-performance transparent polyimides and macrocyclic PI.The main research contents were as follows:(1)Based on sulfoxide bridges group,a series of halogen-free aromatic transparent polyimides(PI)with high optical and thermal properties and low dielectric properties were designed and synthesized,of which the UV cutoff wavelength?₀ was 360?386 nm,the transmittance(T%)was 87.0?87.3%,and the yellow index(YI)was 9.94?17.9,glass transition temperature(T_g)ranged from 293°C to 352°C,dielectric constant was2.05?2.41(1 MHz?1 GHz)and dielectric loss was 0.001?0.01(1 MHz?1 GHz).The results showed that the rigid and twisted sulfoxide unit effectively limited the intramolecular/intermolecular CTC interactions and induced the formation of ordered molecular packing,which further limited the intermolecular CTC interactions and significantly improved the optical properties.(2)Based on the sulfoxide bridging group,a series of fluorine-containing transparent PIs were designed and synthesized.Compared with the typical fluorine-containing transparent PIs,it was found that the fluorine-containing transparent PIs owned better optical and thermal properties.The?₀,T%,YI value,R_th of 6FDA type sulfoxide transparent PI were 327 nm,89%,3.1,and 84.5 nm,respectively.The soluble BPDA type sulfoxide possed a T%of 88.5%,a YIvalue of 3.2,a T_g value of 325°C and a thermal expansion coefficient(CTE)of 24 ppm/K(50?300°C).It was proved that the rigid and twisted sulfoxide group could not only effectively inhibit the intramolecular and intermolecular CTC,but also effectively reduce the molecular molar refractive index and stress-optical coefficient,as well as significantly improve the processing property.(3)Based on performance improvement of fluoride sulfoxide transparent PI,sulfoxide groups was further employed into the multivariate copolymerization system on the engineering research platform to study the relationship between the PAA solution viscosity and diamine content,solid content and polymerization temperature.Besides,a series of fluoride sulfoxide transparent PI film were prepared with the properties of?₀to353?386 nm,T%of 87.1?88.6%,YI value of 3.1?5.6,T_g value of 335?355°C,CTE value of 9?30 ppm/K(50?300°C),showing the application prospect of mass production.(4)A macrocyclic sulfoxide polyimide trimer was designed and synthesized with a specific surface area of 122.4 m²/g and pore sizes of 0.8 nm/0.4 nm.It possessed an ordered molecular stowing structure and molecular recognition function for tetrahydrofuran,which belonged to a new type of molecular cage supramolecular material.