Preparation Of Semi-alicyclic Polyimides And Research On Their Alignment Behaviors For Liquid Crystal Molecules

As one of the most important components for thin film transistor driven liquid crystal display device(TFT-LCD),the performance of the aligment layers for liquid crystal(LC)molecules has great influence on the display quality of the devices.The main types of TFT-LCDs based on the current polyimide(PI)aligment layers,including the twisted nematic(TN-LCD)and in-plane switching(IPS-LCD)devices,have still many defects in optoelectronic features,such as low voltage retention ratio(VHR)and high residual direct current voltage(RDC).Thus,it is urgent to develop new types of PI alignment layers for advanced TFT-LCD applications.In the current work,two isomeric alicyclic dianhydride monomers,including 3,3′,-4,4′-dicyclohexyltetracarboxylic dianhydride(HBPDA)and 3,4-dicarboxyl-1,2,3,4,5,6,7,8-perhydronaphthalene-1-butane dianhydride(HTDA)were first designed and synthsized.The purpose of the molecular design is to improve the solubility of PI resins in organic solvents through the introduction of alicyclic units and to improve the VHR properties of derived PI alignment layers by reducing the charge transfer behaviors of the polymers.Secondly,two types of organo-soluble PI(SPI)resins,HBPDA-PI and HTDA-PIwere prepared by the polymerization of the newly developed alicyclic dianhydrides and commercially available aromatic diamine,respectively.Effects of the introduction of alicyclic structure on the molecular weights and solubility of the two SPI resins were investigated.Then,LC cells were fabricated using the developed SPIs as the alignment layers.Effects of the SPI alignment layers on the optoelectronic properties of liquid crystal cells,including VHR,RDC and pretilt angles(θ_p)of the LC molecules,were systematically investigated.The results indicated that both of the SPI aligment layers could endow the LC cells with good optoelectronic properties.The LC cells based on the HBPDA-PI showed VHR values higher than 96%,RDC values as low as 605 mV,andθp values below 2~o,and optical transmttance high than 97%,which possessing the basic conditions to meet the IPS-LCD requirements.On the other hand,The LC cells based on the HTDA-PI showed VHR values higher than97%,RDC values as low as 880 mV,andθ_p values high than 2~o,and optical transmttance high than 97%,which possessing the basic conditions to meet the TN-LCD requirements.At last,the newly developed HBPDA-PI and HTDA-PI resin were mixed with the polyamic acid(PAA)resin previously developed by our group to afford the mixed"SPI+PAA"alignment layers,MPI-IPS(for HBPDA-PI)and MPI-TN(HTDA-PI),respectively.The fabricated LC cells with the mixed alignment layers exhibited excellent optoelectronic properties,in which the LC cells based on the MPI-IPS showed VHR of 98.05%and the RDC of 170.2 mV;while the ones based on MPI-TN aligment layer had the VHR of 98.33%and the RDC of 292.3 mV.These values all met the practical application requirements of the advanced TFT-LCDs.