CYCLIC OLIGOMER CONSIDERATIONS IN THE SIZE-EXCLUSION CHROMATOGRAPHY OF POLY(ETHYLENE-TEREPHTHALATE)

Room temperature Size Exclusion Chromatography (SEC) for poly(ethylene terephthalate) (PET) was developed using a mobile phase mixture of 5% hexafluoroisopropanol (HFIP) in methylene chloride (MeCl(2)). Calibration was carried out with three different approaches, each time with and without considering the presence of cyclic oligomer in PET samples and standards. At typical concentrations of cyclic oligomer a calibration curve generated from a chromatogram truncated to eliminate the oligomer peak had its slope distorted such that it gave molecular weight average values inaccurate by up to 8%, whereas correcting for the oligomer explicitly resulted in average errors of about 1%. Although the effect of this small peak may be negligible for typical SEC applications involving repeated analysis of similar samples, it may alter the calibration curve significantly if not corrected.