Abstract
Cationic ring-opening polymerization (CROP) of 2-oxazolines is initiated with acylation, alkylation, and silylation on the 2-oxazoline nitrogen. A mild acid initiator for CROP of 2-oxazoline has never been reported. Here we demonstrated that a mild Bronsted acid, diphenyl phosphate (DPP), initiated controlled CROP of 2-ethyl-oxazoline (EtOx) towards PEtOx and its diblock copolymers. PEtOx, with M-w ranging from 3000 to 15 000 g mol(-1), and narrow dispersities (D <= 1.13), was successfully produced by feed molar ratios. The kinetics plot showed that the polymerization was in a two stage mode with a marked acceleration in rate at the early stage. Moreover, the propagation during the late stage proceeded quickly (3.73 x 10(-4) L mol(-1) s(-1)). NMR investigations supported a cationic nature of the initiation with DPP. Novel double-hydrophilic poly(2-ethyl-2-oxazoline)-block-poly(sarcosine) diblock copolymers were synthesized via a one-pot two-step approach.