Determination of ω-end functionalities in tailored poly(2-alkyl-2-oxazoline)s by liquid chromatography and mass spectrometry

Abstract

The in-depth analytical characterization of polymers, in particular regarding intended biomedical applications, is becoming increasingly important to elucidate their structure–property relationships. Specifically, end group analysis of e.g. polymers featuring a ‘stealth effect’ towards the immune system is of particular importance because of their use in coupling reactions to bioactive compounds. Herein, we established a liquid chromatography (LC) protocol to analyse bicyclo[6.1.0]nonyne-functionalized poly(2-alkyl-2–oxazoline)s (POx)s as promising functional polymers that can be applied in strain-promoted click reactions. This work involved the synthesis of poly(2-methyl-2-oxazoline) (PMeOx) and poly(2-ethyl-2-oxazoline) (PEtOx) by living cationic ring-opening polymerization (CROP) with different molar masses ranging from 2 up to 17.5 kDa and, to our knowledge, the first liquid chromatographic analysis of PMeOx. The developed analytical protocol enables the quantitative determination of post-polymerization reaction sequences with respect to the conversion of the ω-end groups. All synthesized polymers were straightforwardly analysed on a C18-derivatized silica monolithic column under reversed-phase chromatographic conditions with a binary mobile phase gradient comprising a mixture of acetonitrile and water. Subsequent mass spectrometry of collected elution fractions enabled the confirmation of the desired ω-end group functionalities and the identification of synthetic by-products.

Keywords

• cationic ring-opening polymerization (CROP)
• liquid chromatography
• poly(2-oxazoline)s (POx)
• matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)
• electrospray ionization mass spectrometry (ESI MS)