New organo-soluble polyimides for optical, microelectronic and fiber applications

A novel class of organo-soluble polyimides has been developed based on monomers containing twisted-biphenyl structures. Thus, 2,2'-disubstituted-4,4'-diaminobiphenyls and 2,2'-disubstituted-4,4',5,5'-biphenyltetracarboxylic dianhydrides have been prepared and polymerized in refluxing phenolic solvents. The polyimides, some of which are soluble in ketone and ether solvents, can be readily solution cast into colorless thin films. The rigid polymer chains align parallel to the substrate surface (in-plane orientation) during the casting process, which results in anisotropy in the film properties. The anisotropy in the refractive index has been used in the development of compensation layers for liquid crystal displays. The polymers have also been dry jet-wet spun from phenolic solutions to afford fibers that display tensile strengths of 3.5 GPa and moduli of 130 GPa.