2D-LC/SEC-(MALDI-TOF)-MS Characterization of Symmetric and Nonsymmetric Biocompatible PEO_<i>m</i>–PIB–PEO_<i>n</i> Block Copolymers

Abstract

Complex copolymer mixtures can be directly analyzed via multidimensional chromatographic techniques after successful synthesis. High-performance liquid chromatography coupled to size exclusion chromatography (LC/SEC) revealed detailed information on the chemical composition, polymeric structure, and molar mass distribution of copolymer mixtures, in particular of symmetric and nonsymmetric α-TEO-ω-PEO telechelic PIB copolymers. A series of azide/alkyne “click” reactions after living polymerization reactions were used to prepare the either symmetric or nonsymmetric PIB–PEO-based triblock copolymers of the general structure (PEOn–PIB–PEOm BCPs (with n = 3; m = 3, 12, or 17)). In order to demonstrate the efficiency of the “click” reaction and thus the purity of the final triblock copolymers, the critical conditions of the PIB-homopolymers (Mn = 3–30 kg mol–1) in the isocratic elution mode (LCCC) were investigated. Thus, it was possible to separate the final polymers from their intermediates using a reversed-phase Atlantis-RP C18 column as stationary phase and a mixture of methyl-tert-butyl ether/methanol (85.34/14.66 (w/w)) as mobile phase. On the basis of the PEO segment length and overall hydrophobicity of the BCPs, we observed a complete separation of the stepwise “click” products. Finally, direct coupling of the 2D-LC/SEC to (MALDI-TOF) mass spectrometric techniques allowed a clear identification of all reaction steps proving the structure of the final symmetric and nonsymmetric triblock copolymers.