Synthesis and characterization of hyperbranched aromatic poly(ether ketone)s functionalized with carboxylic acid terminal groups

A new type of hyperbranched aromatic poly(ether ketone) terminated with carboxylic acid groups (P2) was synthesized via a one-step polycondensation of a symmetric AB₂ monomer, 4,4′-(m-phenylenedioxy)-bis(benzenecarboxylic acid), using phosphorous pentoxide-methanesulfonic acid (PPMA) as a condensing agent and solvent. Subsequently, the terminal carboxylic acid functional group of P2 was converted to an ethyl ester functional group by treatment with thionyl chloride followed by ethanol in the presence of triethylamine. The weight-average molecular weight (M_w) of the ethyl ester-terminated hyperbranched poly(ether ketone) (P3) was measured by gel permeation chromatography. By changing the reaction time and the amount of PPMA, M_w can be controlled in the range of 4.2×10⁴ to 1.6×10⁵. P2 was soluble in polar solvents, and P3 was soluble in less-polar solvents. The thermal stabilities of the poly(ether ketone)s were investigated using thermogravimetric analysis, which indicated that the decompositions of P2 and P3 start at around 150 and 200 °C, respectively. The inherent viscosities of P2 were in the range of 0.101-0.171, while those of P3 ranged from 0.067 to 0.112. The ion exchange capacities calculated by titration were in the range of 2.2-2.8 mol kg^-1 according to the difference in molecular weights. P2 was tested as a weak-acid catalyst and exhibited a certain catalytic activity for the hydrolysis of cellulose to glucose.