Synthesis And Properties Of Cardo Semi-Aromatic Transparent Polyimide

Due to the excellent thermal stability,good mechanical properties and low dielectric constant,polyimide is a high-performance polymer materials,which mainly used in the defense industry,aerospace and microelectronics industries.In the field of optoelectronics,transparent polyimide films can be used as solar cell substrate materials,flexible transparent conductive film substrate materials,etc.However,due to the presence of a highly conjugated structure in the molecular chain of the polyimide,a charge transfer complex having strong absorption of light in the visible light region can be easily formed between the inter-and intra-molecule,leading to the polyimide film exhibit yellow and limit its application in the optical field.In this paper,to improve the transparency of polyimide,the cardo structure is combined with the alicyclic structure,and the effect of the structure of the polymer on its transparency,thermal properties,and solubility is also studied.Works have been mainly conducted as follows:(1)Starting from phenolphthalein,the ester bond in phenolphthalein was replaced with amide bond to synthesize bisphenol monomer,while trans-1,4-cyclohexanediamine was reacted with 4-fluorophthalic anhydride to synthesize 1,4-bis(4-fluorophthalimide)cyclohexane.The bisphenol monomer and the 1,4-bis(4-fluorophthalimide)cyclohexane are polymerized into a series of polyimides by nucleophilic substitution reaction.The series of polyimides can be dissolved in most common organic solvents at room temperature,and can be partially dissolved in tetrahydrofuran,which is a low-boiling solvent,their glass transition temperature exceeds 270 ~oC and can reach up to 316 ~oC,and the temperature at which decomposition occurs at 5%is above 400 ~oC(in nitrogen atmosphere),and the transmittance of the films are almost all above 80%(at 450 nm),which have good transparency.(2)A series of polyimides were synthesized from the cardo fluorene-substituted bisphenol containingpendantmethylgroupsasrawmaterialsandthe1,4-bis(4-fluorophthalimide)cyclohexane monomers with 1,4-cyclohexane by nucleophilic substitution.The influence of fluorene structure and the different trans-/cis-ratios of 1,4-cyclohexane were studied.The series of polymers have good solubility at room temperature,the glass transition temperature is higher than 400 ~oC and can even reach up to 352 400 ~oC,and the temperature when decomposed at5%is higher than 400 ~oC(in nitrogen atmosphere).The transmittances of the polyimide films at400 nm are almost above 80%,and can reach more than 85%at 450 nm,which have excellent transparency.