Synthesis of crosslinkable fluorinated linear-hyperbranched copolyimides for optical waveguide devices



A series of novel crosslinkable fluorinated linear-hyperbranched copolyimides (co-FHBPIs) were prepared by condensation of 1,3,5-tris(2-trifluoromethy-4-aminopheoxy) benzene (TFAPOB), 1,4-bis(4-amino-2-trifluoromethylphenoxy) benzene (6FAPB), and 4,4′-(2-(3′,5′-ditrifluoromethylphenyl)-1,4-phenylenedioxy)-diphthalic anhydride (6FPDA) with different feed ratio, which followed by reaction with 3-ethynylaniline. Under this circumstance, as the TFAPOB/6FAPB ratio increases, the Tg of the polymers decreases gradually from 218 to 199°C, and the Young's moduli decreases from 2.14 to 1.64 GPa. Although, the refractive indices are adjustable in the ranges of 1.5755–1.5631, and the polymer birefringences decrease from 0.0122 to 0.0012 at wave length 650 nm. The polymer films were fabricated by spin-coating and crosslinked by thermal curing. The cured films have good resistance to common organic solvents such as acetone, tetrahydrofuran, N, N-dimethylformamide, dimethyl sulfoxide, and chloroform. The glass transition temperature of E-coFHBPI 50 (the TFAPOB/(6FAPB+ TFAPOB) ratio is 50%)changes from 200 to 243°C after curing, which shows higher thermal stability up to 582°C (5% weight loss). Rib-type optical waveguide device is fabricated by E-coFHBPI 50, which demonstrates an obvious near-field mode pattern of the waveguide. All the results indicated that the polymers are promising candidates for optical waveguide materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013