Oligomer separations by gradient elution high-performance liquid chromatography

Summary Gradient elution high-performance liquid chromatography (HPLC) on chemically modified silica is very suitable for both the qualitative and quantitative analysis of oligomeric mixture, as has been demonstrated for low-molecular-weight resins, pre-polymers and extracts obtained from high polymers and in studying the kinetics of the early stages of polymerization and polycondensation reactions. Examples are given of oligomer separations with epoxy resins, novolak resins, poly-(2,6-diphenyl- p -phenylene oxide). (Tenax), poly(ethylene terephthalate) and poly(ethylene oxide) derivatives. All of these separations easily permit quantification, as has been demonstrated for ethoxylated octylphenol, provided that strict standardization is maintained throughout the analysis. Coefficients of variation of the peak-area measurements of the 19 oligomers observed in this sample were low (1–4%); the coefficients of variation of the retention times ranged from 0.01 to 0.3%. Using commercially available chemically modified column packing materials, the resolution in the gradient elution HPLC of oligomers is adversely affected by size exclusion and sample solubility.