MALDI‐TOF MS investigation of the unconventional termination of living polyoxazoline with ammonia

ABSTRACT Poly(2‐oxazoline) (POx) based materials have experienced renewed interest, due to their biocompatibility and broad functional diversity. Although research pertaining to cationic ring opening polymerization (CROP) of 2‐oxazoline derivatives spans upwards of 5 decades, modern characterization techniques, specifically Matrix Assisted Laser‐Desorption Ionization—Time of Flight Mass Spectrometry (MALDI‐TOF MS), were not available during early studies to aid in identifying polymer end‐groups. Through careful synthesis and analytical characterization, evidence supports an alternative mode of nucleophilic attack during ammonia termination, with nucleophilic attack occurring at a different site on the terminal oxazolinium than where polymer propagation occurs. Furthermore, investigations employing targeted end‐group modification, in conjunction with MALDI and NMR analysis, determined the structure of the resultant terminal group was a hydroxyethylamino end group. Based on the observed data, a mechanistic explanation for the observed 2‐oxazoline ring‐opening termination is proposed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1303–1312 Well‐defined amine terminated poly(2‐oxazoline) is a material of potential utility, and its synthesis was attempted by quenching the living cationic ring opening polymerization of 2‐ethyl‐2‐oxazoline with ammonia. MALDI‐TOF MS analysis provides evidence that is further supported by NMR and titration experiments for an alternative termination phenomenon yielding a hydroxyethylamino terminal group. Based on the observed data, a mechanistic explanation for the observed 2‐oxazoline ring‐opening termination is proposed.