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

Abstract

Polymers bearing amine moieties are highly valuable for their ability to conjugate and/or complex a variety of molecules. However, their incorporation into synthetic macromolecules remains challenging. Poly(2-oxazolines) (POx) are a highly functional class of polymers, which through the choice of polymerization components or post-polymerization modifications, can be furnished with a large range of functional groups. Here, we explored their potential for the preparation of α-amine telechelic macromolecules through a comprehensive comparison of different amine-containing cationic ring-opening polymerization (CROP) initiators comprised of the amine protecting groups tert-butyloxycarbonyl (BOC) and phthalimide and the counterions tosylate (Tos) and bromide (Br). Polymerization kinetics of 2-ethyl-2-oxazoline (EtOx) and stability tests revealed the commercially available phthalimide-NH₂-C3-Br as the most suitable initiator for achieving the highest degree of control over the polymerization. The polymerization initiated by this new initiator at 140 °C under microwave irradiation was characterized by a stable protected amine group, and fast initiation, and delivered well-defined poly(2-ethyl-2-oxazoline)s (PEtOx). α-Amine telechelic PEtOx were subsequently synthesized using different terminating agents, enabling the future preparation of tailored aminated POx-based architectures.