Cross-linkable highly halogenated poly(arylene ether ketone/sulfone)s with tunable refractive index: Synthesis, characterization and optical properties

A series of novel cross-linkable, highly halogenated poly(arylene ether ketone)s (HPAEKs) and poly(arylene ether sulfone)s (HPAESs) with different bromine contents have been designed and prepared by polycondensation reactions for use as optical waveguide materials. The method used for their preparation involved reacting decafluorodiphenyl ketone/sulfone (DFPK/DFPS) with a mixture of 4,4′-isopropylidene bis(2,6-dibromophenol) (4Br-BPA), 4,4′-(hexafluoroisopropylidene)diphenol (6F-BPA), and 1,1-bis(4-hydroxyphenyl)ethyl-1-phenyl-2,3,5,6-tetrafluorostyrol ether (BHPFS). The feed ratio of 4Br-BPA to the total bisphenols varied from 0 to 80 mol.%, while that of BHPFS remained at 20% for all polymers. The resulting polymers have excellent solubility in most common organic solvents such as tetrahydrofuran, cyclohexanone and N,N-dimethylacetamide (DMAc) and can be easily cast into optical-quality thin films. A high glass transition temperature in the range of 164-206 °C was found for these polymers, which could be further increased by about 20 °C upon thermal or photochemical cross-linking. Slab and channel waveguides have been prepared from these polymers. All of them exhibited low optical loss (0.4-0.6 dB/cm) at the telecommunication wavelength of 1550 nm. Due to the relatively higher polarizability of the C-Br bond than that of the C-H bond, an increase in the refractive index was observed as the bromine content in the polymers increased. Consequently, the refractive index of HPAEKs and HPAESs can be readily adjusted within a wide range from 1.51 to 1.57 by simply changing the ratio of the bromine-containing bisphenol in the feed. This variability, along with the excellent cross-linking capability, allows these polymers to be used as both the core and the cladding materials for the waveguide device fabrication and provides a greater flexibility in the design of device structures.