Direct polyesterification of pyridine-2,6-dicarboxylic acid and poly(ethylene glycol) using picryl chloride as condensing agent

High molecular weight polyesters derived from pyridine-2,6-dicarboxylic acid and poly( ethylene glycol) have been synthesized under mild conditions ( room temperature, atmospheric pressure) in the presence of picryl chloride and pyridine. Reaction conditions including solvent, trap agent, reaction time and amount of reagents were investigated using poly( ethylene glycol) 400 as dialcohol comonomer. Detailed analysis of the MALDI-TOF mass spectra of the obtained polyesters has revealed a predominant fraction of macrocycles for a picryl chloride/acid functions molar ratio lower than 1.5. The reaction yielded the most favourable results using 1.5 equivalents of picryl chloride with respect to the acid functions and 4-(N,N-dimethylamino) pyridine as HCl scavenger. The molecular weights of the polyesters at the peak maximum of the SEC trace are in the range of 4 800-80 000 depending on the nature of the comonomer poly( ethylene glycol). Syntheses of an aliphatic and aromatic polyester were also examined.