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] /[I] ) of 25, while the resolution is insufficient at [M] /[I] of 10. Slightly slow initiation is revealed at [M] /[I] = 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.

Poly(2‐ethyl‐2‐oxazoline) Featuring a Central Amino Moiety

“…Any detected minor m/z species did not result from the post polymerization modification reactions at the new central unit but were rather caused by commonly observed CROP side reactions such as proton initiation through chain‐transfer as evident already in P1 . [ 26 ] Additional tandem MS investigations clearly confirmed that (see the Supporting Information).…”

“…Although benzyl bromides are applicable in the CROP of 2‐oxazolines, these attempts resulted in broad molar mass distributions, most likely due to a slow initiation, as has previously been observed for similar initiators. [ 25,26 ]…”

Fundamental Studies on Poly(2-oxazoline) Side Chain Isomers Using Tandem Mass Spectrometry and Ion Mobility-Mass Spectrometry

“…This behavior has its origins in the ejection dynamics which depend on the 3D structure. As already discussed in literature, when the 3D structure changes, the ejection dynamics change [48] (DP [22][23][24][25][26][27][28][29][30][31][32], leading to the correlation between the observed MS/ MS and IM-MS behaviors.…”

“…The increasing compositional and architectural complexity of PAOx and other synthetic polymers developed for advanced applications is giving rise to analytical challenges as the conventional techniques fall short of providing a complete description of the polymer structure (e.g., co-monomer sequence, polymer topologies and branching, isomer identification). PAOx have been the subject of a number of in-depth analytical studies involving mass spectrometry, shedding light on fragmentation pathways [23][24][25], polymerization mechanism [26,27], and unveiling chain transfer reactions [28,29] or the mechanisms associated with polymer degradation [30].…”

Utilization of 4‐(trifluoromethyl)benzenesulfonates as Counter Ions Tunes the Initiator Efficiency of Sophisticated Initiators for the Preparation of Well‐Defined poly(2‐oxazoline)s

“…MALDI ToF MS of the TEGTos‐initiated PEtOx (Figures S28 and S29, Supporting Information) revealed various polymer species: The desired polymer species albeit proton‐initiated species and their resulting species due to the α‐elimination of the proton . The POctOx was not measurable by MALDI ToF MS due to the high molar mass of 11 600 g mol −1 .…”