Well-defined, linear, wholly aromatic polymers with controlled content and position of pyridine moieties in macromolecules from one-pot, room temperature, metal-free step-polymerizations

Synthesis of processable, aromatic pyridine-containing polymers has always been a great challenge. Here, we report for the first time a robust, low-cost synthesis of well defined, high molecular weight, linear, wholly aromatic polymers with rigid ether-bond-free aryl backbones, where the proportion and position of pyridine moieties and spacer lengths between them in the macromolecules are fully controlled. The polymers in nearly quantitative yields, were obtained by one-pot, room temperature, metal-free, non-stoichiometric superacid catalyzed step-polymerization of 4-acetylpyridine (and its mixtures with 2,2,2-trifluoroacetophenone) with multiring aromatic hydrocarbons: biphenyl, meta- and para-terphenyl, para-quaterphenyl, in the mixture of trifluoromethanesulfonic acid with methylene chloride and trifluoroacetic acid. The polymers are highly soluble in most common solvents and form flexible and tough films with tensile strength in the range of 72 - 92 MPa. 1H and 13C NMR analyses of the synthesized polymers revealed high regio-selectivity of the polymer forming reaction affording linear structures with para-substitution in the phenylene fragments of the main chains. The molecular weights of the polymers ranged from 20 000 to 100 000 g/mol, whereas the polydispersity is generally well below 2. The polymers exhibited also high thermostability with Tg ˃ 400 °C, weight loss temperatures (N2, onset) c.a. 485 °C, char yields of 70-75 at 800 °C and high chemical stability. Room temperature reactions of the polymers with methyl(trifluoromethylsulfonate) afford the N-methylated cationic polymers. Certain physical properties and gas separations studies of the polymers are highlighted.