Molar mass, chemical-composition, and functionality-type distributions of poly(2-oxazoline)s revealed by a variety of separation techniques

Detailed characterization of synthetic polymers often required multiple advanced separation technologies since the various molecular distributions present, e.g. polymer molar mass, chemical composition, functionality distributions, etc. are generally mutually dependent. The complexity of polymeric materials necessitates the use of a variety of analytical methods, either in conjunction or in integrated (“hyphenated”) systems. Poly(2-oxazoline) homo- and copolymers with two different side groups rendering the systems hydrophobic, i.e. phenyl and dec-9-enyl substituents, synthesized by living cationic ring-opening polymerization, were investigated. The average chemical composition obtained by pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS) corresponded well with the theoretical composition. The chemical-composition distribution was studied with gradient elution liquid chromatography (GELC) using water and tetrahydrofuran as mobile-phase components. Statistical copolymer samples – in contrast to their block copolymer analogues – revealed two well-separated peaks in GELC. By combining GELC with size-exclusion chromatography (SEC) it was confirmed that the GELC separation was not based on differences in the molar mass. A more likely explanation of the GELC results is the presence of an ionic fraction in the samples of statistical copolymers resulting from either chain-transfer reactions or termination by addition of water. This hypothesis was confirmed with capillary electrophoresis.