The diamine monomers 4

4′-diamino-3

3′-dimethyldiphenylmethane (DMMDA) and 4-diphenyl 3

5-diaminobenzoate (DABBE) were successfully synthesized.Polyimides containing asymmetric units in the main chain and biphenyl pendant groups were synthesized with the copolymerization of DMMDA

DABBE and aromatic dianhydride 4

4′-oxydiphthalic anhydride (ODPA) by chemical imidization.The structures and properties of the resulting co-condensation type polyimides were characterized by IR

GPC

UV-Vis and DSC etc.The polyimides as alignment layers of liquid crystal molecules in liquid crystal display (LCD) were also examined.The polyimides obtained were readily soluble in polar solvents

such as N-methylpyrrolidone (NMP) and N

N-dimethyl form a mide (DMF)etc.The number-average molecular weights of the soluble copolyimides were influenced by the mole ratio of the diamine monomers.It can be observed under POM that the liquid crystals could achieve uniform alignment and a pretilt angle of about 1.8° can be obtained when PI was used as the liquid crystal alignment layer.Moreover

the transmittances of the PIs are more than 80%，and their glass transition temperatures are above 220℃.