Synthesis And Properties Of Fluorine-containing Poly(arylether)s For Optical Waveguide Devices

The continual trend toward high transmission speed,data capability and datadensity in integrated circuits demands a solution to the bottleneck resulting fromthe limited data rate of electrical interconnects. One approach to this problem isthe use of optical interconnection operating with polymer waveguides. Polymermaterials are more and more concerned because of their excellent mechanicalproperties,high thermal optical and electric optical effect,easier processability andlow cost.For the sake of the polymer optical waveguide devices with good properties, theoptical materials have to satisfy several requests as follow: as the products of theoptical communication, the optical polymers should have low loss at two maincommunication windows(1.3 and 1.55μm); High thermal stability ensures thedevices to afford the melting temperature; According to the application ofpolarization-independent wavelength division multiplexes (WDM) devices such asBragg grating filter or arrayed-waveguide gratings (AWG), low birefringence inoptical materials is an important issue which can reduce the polarization dependentloss (PDL); Furthermore, considering the sandwich structure of the waveguidedevices, there must be some difference of refractive index between core andcladding layer to ensure the optical complete reflection, so the refractive indices ofthe polymers must be controlled exactly.Fluorinated poly(aryl ether)s have been emphasized during the last decade becauseof their excellent optical properties such as good optical transparency, highmechanical strength, low moisture absorption, and viable processability, which areessential for polymeric waveguide fabrication. Being an aromatic polymer,however, compared with other amorphous polymers such as poly(methylmethacrylate) (PMMA) or polycarbonate (PC) , they have high birefringencebecause of the rigid nature of the aromatic polymer chains. In term of the design ofmolecule, a serious of crosslinkable fluorinated poly(ether sulfone)s (PESs) basedon (3-trifluoromethyl) phenyl hydroquinone (3F-PH), (3,5-ditrifluoromethyl)phenyl hydroquinone (6F-PH) are prepared via a nucleophilic aromaticsubstitution polycondensation with bis(4-chlorophenyl)sulfone, and the morefluorine-containing crosslinkable poly(aryl ether) (2CF3-PAE-PEP) aresynthesized by 6F-PHand decafluorobiphenyl. All the resulting polymers havehigh molecular weight and thermal stability, that is, the temperature of 5% weightloss are more than 500℃. The reduction of the refractive indices of the polymerscan attribute to the increasing of the fluorine and accretion of the free volume, so itcan control the refractive indices of the polymers in the range of 1.5347-1.578 and1550nm wavelength by means of adjusting the feed mole ration of 3F-PH/6F-PH.Because the introduction of the bulky side group reduces the close packing of themolecular chains which leads to the lower birefringence, all the birefringence ofthe polymers is less than 0.0035. The polymers have low loss at thecommunication wavelength (1.3 and 1.55μm). Especially when the fluorinecontent was increased, the communication regions can also be broadenedcorrespondingly. For example, 2CF3-PAE-PEP only has an absorption peak at1383nm. Meanwhile, most optical-electric devices are as a form of films, so thepolymers must have good solubility. The introduction of the asymmetrical bulkysubstituents results in the good solubility of the polymers, which can dissolve insome common organic solvents, such as N,N-Dimethylacetamide (DMAc) ,N-Methyl-2-Ketopyrrolidine (NMP),Cyclohexanone,Chloroform et al. On theother hand, the polymers show the solvent resistance after crosslinking, whichsatisfies the need of the interbedded technology of the devices. The inner andsurface properties of the films before/after crosslinking are measured by WAXDand atomic force microscopy (AFM). It is found that the polymers have theamorphous structure and lower roughness degree no matter before and aftercrosslinking. Finally a kind of the optical waveguide device---arrayed--waveguidegratings(AWG) is produced using the fluorinated poly(ether sulfone). The AWGmultiplexer exhibits a wavelength channel spacing of 1.60 nm and a centerwavelength of 1550.15 nm, and observes the near-field spot through the infraredcamera, which proves that the synthetic polymers can be used as the materials foroptical waveguide devices.In order to obtain the compact and smooth films after crosslinking, this crosslinkbehavior is studied by way of the isothermal and dynamic thermal kinetics. At lastthe optimum curing condition is determined : 370℃(1h), 380℃(0.5h), 390℃(10min)。That the polymers have the high curing temperature can be explainedby the apparent activation energies, which was obtained by Kissinger and Ozawaequations, namely, 163.63 and 165.96kJ/mol. In addition, the effect ofheat-treatment atmosphere on the near-infrared absorption of the fluorinated poly(aryl ether) is tested by the X-ray photoeletron spectroscopy (XPS) spectrum. Themeasurements show that some of the C-O bonds in the molecule structure will bebroke if the films are crosslinking in the air, which are able to form some newC=O bonds with the oxygen in the air. However the ratios of the groups in themolecule remain the same in the protection of the nitrogen. It is the forth harmonicof the stretching vibration of C=O bond that arouses the absorption loss in the1382nm wavelength.Aimed to reduce the curing temperature ulteriorly, the high fluorinated poly(arylether) terminated with 2,3,4,5,6-Phetafluorostyrene is synthesized. To avoid thebranches and crosslinking in the process of the reaction, a milder reactivecondition---decreasing the reaction temperature and shortening the reaction timeinstead of the traditional method. The resulting polymer has narrowpolydispersities(PI=1.23)and the high thermal stability, whose temperature of the...