Studies on nucleophilic aromatic substitution polymerization for advanced poly(biphenylene oxide)s containing ortho-bis(trifluoromethyl) groups

Abstract

Poly(biphenylene oxide)s (PBPOs) containing two pendent trifluoromethyl groups were synthesized from AB-type monomers, 4’-hydroxy-4-fluoro-3,5-bis(trifluoromethyl)biphenyl and its 3’-hydroxyl isomer. The displacement reaction of fluorine leaving group activated by the two trifluoromethyl groups at the ortho-positions produced high-molecular-weight polymers with $M_n$ up to 101,000 g/mol, indicating the nucleophilic aromatic substitution reaction proceeded effectively. PBPOs with para-, meta-, and mixed ether linkages were obtained and well characterized by FTIR and $^1H/^{19}F$ NMR spectroscopies. All PBPOs were amorphous and soluble in a wide range of organic solvents, and exhibited even more enhanced thermal stability than the previously reported two meta-trifluoromethyl substituted analogues. Increasing the para-linkage fraction in the polymer generally improved solubility and increased $T_g$ in contrast to the meta-trifluoromethyl case, where para-linked polymer was poorly soluble and semicrystalline. This suggests that the ortho-trifluoromethyl substituents are more effective for the synthesis of para-linked PBPOs. They also showed low refractive indices and birefringence values.