Novel, Metal-Free, Superacid-Catalyzed “Click” Reactions of Isatins with Linear, Nonactivated, Multiring Aromatic Hydrocarbons

A novel series of linear, high-molecular-weight polymers was synthesized by one-pot, metal-free superacid-catalyzed reaction of isatins (1a−d) with linear, nonactivated, multiring aromatic hydrocarbons: biphenyl (A), p-terphenyl (B), p-quaterphenyl (C), 2-(4-biphenylyl)-6-phenylbenzoxazole (D), 9H-fluorene (E), 9,9-dimethyl-9H-fluorene (F), 2,2′-[2,5-bis(trifluoromethyl)-1,4-phenylene]bis(9,9-dimethyl-9H-fluorene) (G), oligo-9,9-bis(2,6-ethylhexyl)-9H-fluorene (H), biphenol (I), and bi-2-napththol (J). The reactions were performed at room temperature in the Brønsted superacid trifluoromethanesulfonic acid (CF3SO3H, TFSA) and in a mixture of TFSA with methylene chloride or TFA tolerant of hydroxyl, carboxy, and cyano groups. The polymers obtained were soluble in most common organic solvents, and flexible transparent films could be cast from the solutions. 1H and 13C NMR analyses of the polymers synthesized revealed their linear structure with para-substitution in the phenylene fragments of the main chain. The molecular weights M w and M n of the polymers ranged from 54200 to 742000 and from 40140 to 438500 g/mol, respectively. Most of the polymers also possess narrow polydispersity (1.15−1.50). The oxindole groups of the polymers react smoothly with alkyl bromides under basic conditions in N-methylpyrrolidinone (NMP). The amount of “click”able allyl- and propargyl- functionalities is readily controlled by adjusting the reaction ratio of polymer to alkyl bromides. The demonstrated efficiency and orthogonality of isatin-based polymer chemistry shows it to be an essential addition to the family of polymer “click” reactions.