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

Abstract

During the last decades, poly(2‐oxazoline)s (POx) have gained increased interest due to their versatility. In particular, cationic ring‐opening polymerization (CROP) enables the synthesis of well‐defined polymers bearing quantitative α‐ and ω‐functionalities. In contrast to small initiating groups, the introduction of more sophisticated, respectively demanding groups remains challenging. To fulfill this challenge, the initiator should comply with one major requirement in order to yield well‐defined polymers: a fast and complete initiation. The straight forward two‐step synthesis of a novel initiator containing a 4‐(trifluoromethyl)benzenesulfonate (fluorylate, TosCF3) counter‐ion is herein presented to accomplish the introduction of a sophisticated functional 3‐(2‐(2‐ethoxy)ethoxy)ethoxy)prop‐1‐ene (TEG) initiating group. Kinetic studies are conducted in acetonitrile and chlorobenzene using the hydrophilic 2‐ethyl‐2‐oxazoline (EtOx) as well as the hydrophobic 2‐octyl‐2‐oxazoline (OctOx) as monomers to examine the influences of the solvent as well as the different monomers. In particular, the initiator efficiency is determined by 1H and 19F nuclear magnetic resonance spectroscopy and compared to the corresponding tosylate (TEGTos) and triflate (TEGTf). It is shown that the fluorylate combines the stability of the tosylate and an enhanced propagation rate comparable to the triflate.

Protected amine-functional initiators for the synthesis of α-amine homo- and heterotelechelic poly(2-ethyl-2-oxazoline)s

“…The M n,th was calculated by multiplication of monomer conversion and the theoretical [M]/[I] ratio assuming a quantitative initiation. When the initiator consumption was taken into consideration, 65 the M n , exp values were notably higher at every time point compared to M n,th . This might also explain the higher M n,SEC for the phthalimide-NH 2 -C3-Tos initiated polymerization (Fig.…”

“…1b), possibly underpinning variable concentration of propagating species throughout a significant part of the polymerization. 65,66 All the initiators showed relatively broad molar mass distributions with the molecular weight dispersity (Đ) ranging from 1.25 to 1.46 (Fig. 1c).…”

Quasiliving cationic ring-opening polymerization of 2-ethyl-2-oxazoline in benzotrifluoride, as an alternative reaction medium

“…In general, the equilibrium between the cationic and covalent species is shifted toward the propagating oxazolinium ion with increasing solvent polarity, which leads to higher polymerization rates [4]. So far, several solvents, such as acetonitrile [9][10][11][12][13][14][15][16][17][18][19][20][21][22], butyronitrile [13,23], chlorobenzene [10,14,21], chloroform [24], dichloromethane [25], dimethylacetamide [8,10,[26][27][28], ionic liquid [29], nitrobenzene [18], nitromethane [30], and sulfolane [10,31,32] have been reported as polymerization media for the CROP of 2-oxazolines. Up to now, acetonitrile is far the most common solvent used for oxazoline polymerization.…”