Poly(arylene ether)s with low refractive indices: poly(biphenylene oxide)s with trifluoromethyl pendant groups via a meta-activated nitro displacement reaction

Abstract

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 meta-activated nitro displacement reaction. The displacement of nitro leaving group activated by the two trifluoromethyl groups at the meta-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 meta-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, p-PBPO and m-PBPO, 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 (T 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.