Macropropagation Rate Coefficients and Branching Levels in Cationic Ring-Opening Polymerization of 2-Ethyl-2-oxazoline through Prediction of Size Exclusion Chromatography Data

Abstract

A systematic kinetic study of the isothermal cationic ring-opening polymerization of 2-ethyl-2-oxazoline (EtOx) in acetonitrile initiated by methyl tosylate under microwave irradiation (353-413 K) for a target degree of polymerization of 100 is reported as a basis for kinetic Monte Carlo simulations with parameters tuned based on monomer conversion and chain length data. It is highlighted that the size-exclusion chromatography (SEC) trace is needed to properly tune the less known macropropagation rate coefficient, which is related to the incorporation of enamine-terminated polymer chains resulting from chain transfer to monomer and which determines the contribution of linear and branched chains. A model-based design is applied to identify the reaction temperatures that lead to an optimum between the reaction time and control over molecular properties. A linear relationship is derived, which can be used to reliably assess the mass fraction of branched chains at sufficiently high monomer conversions based on the measurement of the location of the inflection point for the high molar mass part of the SEC trace.