Synthesis of aromatic polyketones by nonstoichiometric Friedel-Crafts polycondensation using AlCl3

Aromatic polyketones without ether linkages in the main chains were successfully synthesized. Polycondensations were performed between aromatic dicarboxylic acid chlorides and 2,2'-dimethoxybiphenyl (DMB) based on Friedel-Crafts acylation using 5 equivalents of AlCl3 relative to the total amount of monomers. High-molecular-weight polymers were obtained under both stoichiometric and DMB-excess nonstoichiometric conditions. It was found that the equimolar reaction between DMB and benzoyl chloride, using excess AlCl3, selectively yielded a diacylated compound, indicating that the second acylation was much faster than the first. The detailed NMR analysis of DMB and a monoacylated compound revealed that AlCl3 coordinated to the methoxy groups of DMB, and the monoacylated compound with AlCl3 formed a mixture of the compound with AlCl3-coordinated and uncoordinated methoxy groups. The second acylation was determined to be more rapid because the AlCl3-uncoordinated monoacylated compound showed higher reactivity than the AlCl3-coordinated DMB. The change in reactivity before and after the first acylation involved the coordination and dissociation of AlCl3, which plays a key role in the nonstoichiometric polycondensations. The polycondensations presented in this paper are advantageous because high-molecular-weight, rigid, thermally stable, and soluble aromatic polyketones can be obtained without the precise feed control of moisture sensitive dicarboxylic acid chlorides or the use of toxic and expensive superacids.