Synthesis of high regular poly(ethylene succinate) by adding oxalic acid in poly-condensation system: Suppressing etherification side reaction

Poly(ethylene succinate) (PES) with high chain regularity was synthesized by adding oxalic acid in the melt poly-condensation system. The molar ratios of diethylene glycol succinate (DEGS) units in the polymer chains were diminished from 3.8% to 0.6% when 17 mol% oxalic acid was added. Oxalic acid underwent esterification with ethylene glycol and decarboxylation , producing ethylene glycol monoformate and formate end-capped PES oligomers . The formate endcapping supressed the etherification side reactions. Ethylene glycol formate with a lower boiling point was more easily released by-production than ethylene glycol during the transesterification stage, resulting in a faster transesterification rate. Meanwhile, the molecular weights significantly increased. The high chain regularity endowed the PES with higher melting temperatures of 105 °C and remarkably increased crystallization rates. The mechanical properties , including tensile strength at break, were simultaneously improved for a high-molecular-weight PES sample ( M w  = 100 kg/mol).