Poly(arylene ether)s with Low Refractive Indices: Poly(biphenylene oxide)s with Trifluoromethyl Pendant Groups via a Meta-Activated Nitro Displacement Reaction

High-molecular-weight poly­(biphenylene oxide)­s (PBPO) were prepared from AB-type monomers, 4′(3′)-hydroxy-4-nitro-2,6-bis­(trifluoromethyl)­biphenyl, through a <i>meta</i>-activated nitro displacement reaction. The displacement of nitro leaving group activated by the two trifluoromethyl groups at the <i>meta</i>-position produced high-molecular-weight polymers, which implies that nucleophilic aromatic substitution reaction of the nitro leaving group proceeded very effectively with two activating groups at the <i>meta</i>-position. The obtained polymers have weight-average molecular weight of 20 800–143 300 g/mol and molecular weight distribution of 1.68–2.85. While two homopolymers of 4′- or 3′-hydroxy-4-nitro-2,6-bis­(trifluoromethyl)­biphenyl, <i><b>p</b></i><b>-PBPO</b> and <i><b>m</b></i><b>-PBPO</b>, showed a semicrystalline morphology, copolymers of the two monomers were amorphous and dissolved in a wide range of organic solvents. The PBPOs possessed a high glass transition temperature (<i>T</i>_g) in the range of 169 to 208 °C depending on their structure and high thermal stability with 10% weight loss temperatures from 486 to 542 °C in nitrogen and from 465 to 516 °C in air. Moreover, PBPOs containing two trifluoromethyl groups showed low refractive indices in the range of 1.4979–1.5052 as well as low birefringence values of 0.0095–0.0148