Despite that the cationic polymerization of 2-oxazolines is commonly denoted to be living, a clear high molar mass fraction appears in the size exclusion chromatography traces, especially when performing the polymerization at higher temperatures. This formation of the higher molecular weight fraction still remains a puzzle, albeit it has recently been proposed to be due to a combination of intrinsic chain transfer based on the β-elimination1 and oxazolinium chain end-tautomerisation.2 But, the high molecular weight formation during the polymerization of 2-phenyl-2-oxazoline (PhOx) remains unanswered. In the quest to understand the puzzle we investigated the effect of the polymerization time (at 140 °C) of various 2-oxazoline monomers on the high molecular weight formation. We observed gradual increased in intensity of the high molecular weight fraction in the SEC traces with prolonged time. Here we propose another possible mechanism for chain coupling: the attack of the active chain ends onto already formed polymer amide nitrogen atoms, which becomes sterically hindered with the increased polymerization and becomes reactive as observed in case of sterically hindered amides.3

What is the shoulder? Understanding the appearance of the higher molecular weight fraction in the size exclusion chromatography from the synthesis of poly(2-alkyl-2-oxazoline)s

2019 Spring National Meeting

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