Phenylethynyl-terminated Fluorinated Polyimides For Optical Waveguide Device

In recent years, as one of the three pillars of modern communication network, optical fiber communication have been rapid growth.Many countries devoted a large number of manpower and resources to the seminars.As one of the basic components in optical fiber communication, optical waveguide devices have received increasing attention. Polymer materials were introduced to optical waveguide devices under development for its excellent workability, facile construction technology, strong chemical stability and low cost.The polymer optical materials should satisfy several requirements. First, it should have a low optical transmission loss especially at the telecommunication wavelength region of 1310 and 1550 nm.Second, in order to ensure that the small radius of curvature of polymer waveguide, it should have tunable refractive index (RI). Third, it should have the low birefringence to avoid polarization dispersion. Last, in order to adapt to the different devices use environment, materials should have excellent thermal stability, chemical stability and low water absorption. Fluorinated polyimide materials with its excellent thermal stability, good solubility, light transmittance and low moisture absorption rate have received the people's attention. As the waveguide material to its corresponding wide range of studies carried out up.A great deal of effort has been concentrated on the preparation of polyimides containing crosslinkable moieties.For the fabrication of awaveguide device, a crosslinked polymer system has several advantages such as increased thermal and thermo-stability, chemical resistance, gap filling ability, and improved adhesion properties at the substrate. Containing phenylethynyl moieties polymers are good candidates for crosslinked optical waveguide materials due to easy synthesis, absence of an aliphatic C–H bond leading to significant optical absorption loss, greater process control over the ethynyl group due to its wider processing window,and absence of catalyst and evolution of any volatile during the curing reaction. The incorporation of phenylethynyl moieties into polymers has been studied extensively. The most common approach has been to introduce the phenylethynyl groups as end caps on oligomers which can then be molded into the final shape and subsequently crosslinked by heating.In the first part, we designed and synthesized a series of phenylethynyl terminated fluorinated polyimide oligomers using [1,4-(4-amino-2- trifluoromethyl-phenoxy)-2-(3'- trifluoromethylphenyl)benzene] as a diamine, 4,4'-(Hexafluoroisopyrilidene) diphthalic anhydride (6FDA) and 4,4'-Oxydiphthalic anhydride (ODPA) as dianhydrides and 4-(1-phenylethynyl)- 1,8-naphthalic anhydride (PENA) as an endcapping reagent. The oligomers were thermally crosslinked at 370°C for 2 h and showed high thermal stability. The temperatures at 5% weight loss were up to 540°C under nitrogen atmosphere. These PETI oligomers exhibited very good solubility behavior at room temperature both in strong aprotic solvents and in common organic solvents. After crosslinking, they have good chemical resistance, so it will not cause intermixing by solvents between layers by spin-coating. Also, they have low inherent optical absorption at the near-infrared region for polymeric optical waveguide materials. The refractive indexs of their films were controlled in the range of 1.5515–1.5976 at 1550 nm.In the second part, the fluorinated triamine monomer and commercially available dianhydride monomers were condensed to afford a series of anhydride-terminated poly(amic acid)precursors, then the precursors were end-capped by 3-trifluoromethyl-4-(phenylethynyl) aniline (3FPA) and chemically imidized to yield a series of phenylethynyl -terminated hyperbranched polyimides (HBPIs). These HBPIs were readily soluble in a variety of organic solvents such as NMP, DMF, THF, and cyclohexanone. The good solubility of these polymers in common organic solvents is profitable for the fabrication of the films for waveguide optical devices. We can see that the introduction of phenylethynyl crosslinkable groups at the end of the polymer is helpful for the fabrication of multilayered optical waveguides. We test the near-infrared absorption of our polymers.At the key telecommunication wavelengths of 1310 and 1550 nm, both polymer films show low light absorption. Such types of fluorinated hyperbranched polyimides are potentially useful for optical waveguide applications.