Synthesis of hyperbranched fluorinated polymers with controllable refractive indices

Abstract

INTRODUCTIONPolymers containing fluorine atoms (fluorinated polymers) exhibit increased thermal stability, hydrophobicity, improved chemical resistance and decreased intermolecular attractive forces in comparison with their hydrocarbon analogs. These properties are derived from the fundamental atomic properties of fluorine, such as high ionization potential, low polarizability and high electronegativity. 1 The high ionization potential, combined with the low polarizability, leads to weak intermolecular interactions, which in turn leads to low-surface energy and low refractive indices of fluorinated polymers. Recently, fluoropolymers have received considerable attention as high-performance materials for applications in optoelectronic fields. Specifically, the refractive index is a very important property of polymers for photonic applications, for which highly fluorinated polymers such as Teflon (DuPont, Wilmington, DE, USA) and CYTOP (ASAHI GLASS CO., LTD., Tokyo, Japan) are well known and widely used in optical communication networks. Current optical communication networks are based on silica optical fiber and devices. To integrate with these devices and materials, and to reduce the optical loss, polymer materials with refractive index values close to that of the silica materials (1.46) are desired. 2 Therefore, materials with a controllable refractive index are required for the successful design and fabrication of photonic devices. For example, the widely used fluorinated polyimides usually have relatively low refractive indices 3 and this value can be easily manipulated by introducing polar groups and copolymerizing with comonomers containing heavier atoms, such as bromine to give high refractive indices. However, it appears difficult to lower the refractive index. We have modified fluoropolymers with the simple polyaddition of bis(epoxide)s with dicarboxylic acids and diols in the presence of quaternary onium salts and they exhibited a linear relationship between refractive indices and fluorine contents of the polymer. 4,5 Similar investigations have been conducted with fluorinated aromatic-aliphatic copolyethers, 6 fluorinated poly (phthalazinone ether)s 7 and hyperbranched fluorinated polyimides. 8 The relationship between the refractive index (n D ), density (r g cm À3 ), molecular weight (M g mol À1 ) and molecular refraction (R cm 3 mol À1 ) of a polymer is described by the Lorentz-Lorenz equation (Equation 1). 9According to the Lorentz-Lorenz equation, the polymers with low r give low n D . That is, hyperbranched polymers (HBPs) are good candidates for the production of low-density polymers because of their three dimensional globular architecture with higher branched structure. 10 Recent study has indicated that hyperbranched structures have an increasingly important role in reducing crystallinity, to avoid significant optical loss. For example, we have observed and reported that the HBPs show no birefringence due to their highly branched globular structure, preventing their polymer orientation. 11 On t...

Anti-Reflection Coatings on 3D-Printed Components

“…The reduced refractive index of VC supports the presence of fluorination and is consistent with the shift to shorter wavelengths seen in Figure 2. In addition to polymerisation rates, it is well-known that the index will decrease with increasing fluorine content because of fluorine's large electronegativity [19]-the large drop we measure suggests the concentration [F] is in excess of 20 wt.%.…”

“…Coatings 2021, 11, x FOR PEER REVIEW 5 of 10 increasing fluorine content because of fluorine's large electronegativity [19]-the large drop we measure suggests the concentration [F] is in excess of 20 wt.%.…”

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“…[2] An interesting feature of this motif is the presence of alarge number of fluorine atoms, which renders them as promising contrast agents for 19 FMRI. [4] Theh exafluoroisopropanol group can also be found in ligand design, either by merit of its inductive electron-withdrawing properties or as abulky substituent. [3a] Furthermore,a ryl a,a-bis(trifluoromethyl)carbinol-containing polymers display excellent material properties,a swell as high thermal stability and flame resistance.…”

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