Bifunctional Initiators as Tools to Track Chain Transfer during the CROP of 2-Oxazolines

Abstract

Detailed kinetic studies during the cationic ring-opening polymerization (CROP) of 2-ethyl-2-oxazoline (EtOx) are conducted using four bifunctional bromo-type initiators in N,N-dimethylformamide (DMF) at 140 °C. Serving as models to quantify chain transfer to monomer occurring during the CROP initiated by monofunctional initiators, size exclusion chromatography (SEC) resolves a second molar mass distribution with lower molar mass at initial [monomer] to [initiation site] ratios ([M]₀ /[I]₀ ) of 25, while the resolution is insufficient at [M]₀ /[I]₀ of 10. Slightly slow initiation is revealed at [M]₀ /[I]₀ = 25, which prohibits the derivation of chain transfer rates by fitting of the size exclusion chromatography (SEC) data. Although conventional kinetic plots give no indication of significant amounts of chain transfer, the molar mass distributions resolved by SEC can unambiguously be identified as such by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) in both the high as well as the low m/z regions of the mass spectra.

Keywords: bifunctional initiators; cationic ring-opening polymerization; chain transfer; matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS); poly(2-ethyl-2-oxazoline).