A novel diamine monomer, containing fluorine and phosphine oxide, bis(3-aminophenyl)-3,5-bis(trifluoromethyl) phosphine oxide (mDA6FPPO), was prepared via Grignard reaction from diphenylphosphonic chloride and 3,5-bis( trifluoromethyl)bromobenzene. First, 3,5bis(trifluoromethyl)phenyl diphenyl phosphine oxide (6FPPO) was prepared and subjected to nitration and reduction to obtain mDA6FPPO. The monomers were characterized by FT-IR, H-1-NMR, P-31-NMR, F-19-NMR, titrator and elemental analyzer (EA). The monomer was then utilized to prepare polyimides with dianhydrides such as 6FDA, BTDA, ODPA or PMDA by the conventional two-step method; preparation of poly(amic acid), followed by solution imidization. The polyimides were characterized by FT-IR, NMR, DSC and DMA, with intrinsic viscosity, refractive index and adhesive properties also being evaluated. A phosphine oxide containing monomer, bis(3-aminophenyl) phenyl phosphine oxide (mDAPPO) and a commercial 3,3'-diaminodiphenylsulfone (mDDS) were also used for comparison. The polyimides with mDA6FPPO exhibited high T-g (228-281 degreesC). good thermal stability, very low birefringence (0.001) and good adhesive properties.