Characterization of oligomeric polypropyleneglycol acrylate by GC, SFC and MALDI-TOF-MS.

Polypropyleneglycol acrylate (PGA), one of the typical acrylic oligomers manufactured industrially, was comprehensively characterized by gas chromatography (GC), supercritical fluid chromatography (SFC) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The homologous series of polypropyleneglycol diacrylate (DA), polypropyleneglycol monoacrylate (MA), and unreacted polypropyleneglycol (PG) were observed as Na adducts in the MALDI-MS spectra of the PGA samples. The relative intensities of these peaks reflect the distributions of the homologues, although their accurate quantification was generally difficult because of change in the ionization efficiency depending on the chemical structure and the molecular weight of the species. On the other hand, the DA and the MA homologues were observed in the chromatograms obtained by SFC in a temperature-programming mode, while the PG homologues were not detected under the given SFC conditions using UV detection. Here, the determination of the degree of polymerization of each component in the chromatograms was accomplished through SFC fractionation for the corresponding peaks, followed again by MALDI-TOF-MS measurement. Furthermore, most of the components in the PGA samples were almost completely separated in the resulting gas chromatograms, and their unequivocal assignments were made also using the retention data on the gas chromatograms of the SFC fractions. As for the quantitative analysis, the relative abundances among DA, MA and PG for lower degrees of polymerization can be easily calculated based on the observed gas chromatograms, whereas the distribution of DA and MA can be estimated from the observed SFC data even for the relatively higher molecular weight fractions, which are generally difficult to determine accurately by GC because of their lower volatility. These results demonstrated that even the complex PGA samples were able to be characterized in detail by using GC, SFC and MALDI-TOF-MS complementarily.