Preparation of poly(2-oxy-6-naphthoyl) and copolymers using reaction-induced phase separation during direct polymerization in the presence of boronic anhydride

Poly(2-oxy-6-naphthoyl) (PON) was obtained as precipitates by direct polymerization of 2-hydroxy-6-naphthoic acid (HNA) in the presence of boronic anhydrides such as 2,4,6-tris(3,4,5-trifluorophenyl)- 1,3,5,2,4,6- trioxatriborinane (TFBA) and 2,4,6-tri(biphenyl-4-yl)-1,3,5,2,4,6- trioxatriborinane (BPBA). The polymerizations were carried out in an aromatic solvent at 300°C for 24 h. Both morphology and molecular weight of the PON precipitates were considerably influenced by not only the structure of the boronic anhydride but also its concentration (c_B). Spheres with needles on their surface were formed in the polymerization with TFBA at c _B of 50-70 mol%, and those having smooth surface were obtained at c_B of 100 mol%. The M_n increased with the value of c _B in the range from 2.7 x 10³ to 9.0 x 10³. Aggregates of cone-like crystals were prepared in the polymerization with BPBA at c_B of 10-30 mol%, and spheres having rugged surface were formed at c_B of 50-100 mol%. The M_n also increased with the value of c_B in the range from 5.4 x 10³ to 12.9 x 10 ³. These PON precipitates possessed high crystallinity in spite of the morphology. The copolymerization of HNA and 4- hydroxybenzoic acid (HBA) was also examined in the presence of BPBA at c_B of 100 mol% with varying the content of HBA in feed (r_f). Copolymers were obtained as spheres of which the content of 4- oxybenzoyl moiety was lower than the value of r _f due to the difference in the solubility of the oligomers.