Direct UV-written highly fluorinated aromatic-aliphatic copolyethers for optical waveguides

A bisphenol monomer (4-methoxy) phenylhydroquinone (Me-HQ) was prepared and further polymerized with 2,2,3,3,4,4,5,5,6,6,7,7-dodeca-fluoro-1,8-octanediol (12F-diol) and decafluorobiphenyl (DFBP) to obtain highly fluorinated aromatic-aliphatic copolyethers containing methoxy groups. After demethylation and the reaction with epoxy chloropropane, a series of novel highly fluorinated aromatic-aliphatic copolyethers bearing epoxy groups (FA-APE EP) at different feed ratios of (Me-HQ)/(12F-diol) were obtained. The chemical structures of all the copolymers were analyzed by 1H NMR, 13C NMR and 19F NMR spectra. A series of highly fluorinated photoresists were prepared by composing of fluorinated copolyethers, diphenyliodonium salt as a photoacid generator (PAG) and solvent. After UV-curing, the cross-linked films exhibited excellent chemical resistance and high thermal stability (Td ranged from 230 to 278 °C). The refractive indices of the films could be controlled between 1.5127 and 1.4749 at 1550 nm by varying the feed ratio of comonomers. A clear negative pattern was obtained through direct UV exposure and chemical development. For waveguides without upper cladding, the propagation loss of the channel waveguides was measured to be 0.18 dB/cm at 1550 nm.