Fluorinated polymaleimides with high thermal stability and low optical absorption loss in the optical communication wavelength of $1.55{mu}m$ were investigated for application in low-loss waveguide materials. The fluorinated polymaleimides were prepared from two monomers phenylmaleimide (H-PMI) and pentafluorophenylmaleimide (F-PMI). All synthesized copolymers had high thermal stability (decomposition temperature $(T_d)=380-430^{circ}C$). The refractive index of the copolymers could be tuned from 1.4969 to 1.5950 in the TE mode and from 1.4993 to 1.5932 for the TM mode at 632.8 nm by copolymerizing different weight ratios of H-PMI and F-PMI. The refractive index of the copolymers decreased with increasing F-PMI content. In addition, when the amount of F-PMI was increased, optical loss and absorption loss at 632.8 nm and 1550 nm, respectively, decreased.