Macrocycles. 15. The Role of Cyclization in Kinetically Controlled Polycondensations. 1. Polyester Syntheses

Various diols were polycondensed with dicarboxylic dichlorides in the presence of pyridine or γ-picoline. Aliphatic dicarboxylic acid dichlorides were reacted with 1,4-butanediol, catechol resorcinol, methylhydroquinone or bisphenol A. Isophthaloyl chloride was polycondensed with α,ω-dihydroxyalkanes, methylresorcinol, or 4-methylcatechol. The resulting polyesters were characterized by 1 H NMR spectroscopy and SEC measurements. When the reaction products were analyzed by MALDI−TOF mass spectrometry, cyclic oligo- or polyesters were found to be the main products in all cases. The cycles were the only detectable products, when the reaction conditions were optimized for complete conversion and highest molecular weights. These results together with previously published results definitely prove in agreement with theoretical considerations that cyclizations are an inherent and necessary component in step-growth polymerizations conducted under ideal conditions (no side reaction and equilibrations, perfect stoichiometry, and homogeneous phase). Furthermore, cyclizations are a decisive limitation of the chain growth even under ideal conditions. Therefore, these results also indicate that the “Carothers equation” represents in two points a misleading description of step-growth polymerizations.