Anionic polymerization of activated oxetane and its copolymerization with ethylene oxide for the synthesis of amphiphilic block copolymers

The synthesis of polyoxetane (POx) and amphiphilic block copolymers composed of poly(ethylene oxide) (PEO) and polyoxetane was achieved by anionic ring-opening polymerization and monomer activation. First the anionic polymerization of oxetane was conducted using an initiating system based on tetraoctylammonium bromide associated with a simple trialkylaluminum, NOct₄Br/i-Bu₃Al (1/>1). This methodology allowed the controlled synthesis of polyoxetanes with molar masses up to 10 000 g mol⁻¹ and a narrow molar mass distribution (Đ < 1.2). The synthesis of diblock copolymers was achieved starting from a mixture of ethylene oxide and oxetane, thanks to their difference in reactivity. The micellization of PEO-b-POx in water was studied as a function of temperature with a shrinking phenomenon appearing at around 33 °C. Finally, a two-step procedure is also discussed for the synthesis of polyoxetane-b-poly(ethylene oxide)-b-polyoxetane triblock copolymer.