Study On The Preparation And Performance Of Polyimides With Solubility And High Optical Transparency

In recent years, PI has been concerned widely for its excellent thermal stability, significant mechanical strength, prominent insulation performance, outstanding dimensional stability and so on. So it has been used widely such as microelectronics, photoelectron, car, aeronautics, gas separation and composite materials. But, this kind of polymer has very strong rigidity usually, and it often does not dissolve in the conventional reagents. Besides, it is hard to process because of its high melting point. Moreover, most reported PIs show dark yellow or brown color, which all limit its application.To improve the disadvantages, scientists had made lots of attempts, such as the introduction of the flexible groups, bulky groups, pendant loop groups, suspension loop structure, non-coplanar and unsymmetrical structures into the polymer backbones. In the subject research, it mainly introduces the bulky substituents, unsymmetrical structures and fluoride group to the polymer molecular chain to improve its solubility and optical performance. This topic mainly from the following several parts:(1) Through molecular design, two kinds of new diamine monomer(3,3’-ditertbutyl-4,4’-diaminodiphenyl-4’’-tertbutylphenylmethane and 3,3’ –ditertbutyl-4,4’-diaminodiphenyl-4’’-naphthylmethane) were obtained. Then reacted with five commercial aromatic dianhydride to get a series non-coplanar polyimide of large side-isopropyl, large ring-side. Then, the structure and properties of the polymer were studied. The results showed that the solubility and optical performance of the PIs improved significantly, and maintained its good mechanical properties and low dielectric constant.(2) 2-Isopropylaniline reacted separately with 3,4-difluorobenzaldehyde and 4-(trifluoromethyl)benzaldehyde to get 2 diamine monomer(3,3′-diisopropyl-4,4′-diaminodiphenyl-3′′,4′′-difluorotoluene and 3,3′-diisopropyl-4,4′-diaminodiphenyl-4′′-trifluoromethyltoluene), then used IR, NMR to measure the structure of monomers. A series of PIs were obtained by condensation polymerization with the four aromatic dianhydride via one-step method. The results indicated that the solubility and optianl transparency of PI were improved obviously.(3) 4-phenylbenzaldehyde and 2-isopropylaniline were used to get a new diamine monomer 3,3′-diisopropyl-4,4′-diaminodiphenyl-4′′-phenyltoluene. Then, with m-Cresol as solvent, reacted with 5 commercialization dianhydrides to obtain various PIs which have large rings, bulky substituents and non-coplanar. In the last, the results of test indicated these polymers showed excellent solubility in common solvents, and even dissolve in low boiling point, such as CH2Cl2 and acetone at room temperature, and the cutoff wavelength in the rage of 305-365 nm, which showed good optical performance.