Isolation and identification of cyclic oligomers of the poly(ethylene terephthalate)-poly(ethylene isophthalate) copolymer

New cyclic oligomers of the copolymer of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI) were isolated and identified. A condensation polymerization was carried out at a high temperature, and the solid‐state polymerization that followed yielded the high molecular weight polymer. The oligomers were extracted from the high molecular weight PET–PEI copolymer and separated with preparative high performance liquid chromatography techniques. Their chemical structures and properties were analyzed and determined by 1H NMR, differential scanning calorimetry, and mass spectroscopy. The oligomers observed at early retention times were a cyclic dimer and cyclic trimers and consisted of [GT]3, [GI]2, [GI]3, [GT]2[GI]1, and [GT]1[GI]2. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 881–889, 2003 The cyclic oligomers of poly(ethylene terephthalate) (PET), poly(ethylene isophthalate) (PEI), and the PET–PEI copolymer that formed during the polymerization of isophthalic acid and/or terephthalic acid with ethylene glycol were analyzed, and their properties and contents were determined. A condensation polymerization was carried out at a high temperature, and the solid‐state polymerization that followed yielded the high molecular weight polymer. The oligomers were extracted from the high molecular weight PET–PEI copolymer and separated with preparative high performance liquid chromatography techniques. Their chemical structures and properties were analyzed and determined by 1H NMR, differential scanning calorimetry, and mass spectroscopy. The oligomers observed at early retention times were a cyclic dimer and cyclic trimers and consisted of [GT]3, [GI]2, [GI]3, [GT]2[GI]1, and [GT]1[GI]2.