Controlled Synthesis of an ABC Miktoarm Star-Shaped Copolymer by Sequential Ring-Opening Polymerization of Ethylene Oxide, Benzyl β-Malolactonate, and ε-Caprolactone

This paper reports on the synthesis of an amphiphilic miktoarm ABC star-shaped copolymer, s[(PEO)(PMLABz)(PCL)], consisting of biocompatible/bioresorbable arms. Indeed, PEO is a hydrophilic biocompatible poly(ethylene oxide) arm, PMLABz is a poly(benzyl β-malolactonate) arm precursor of a pH-sensitive bioresorbable poly(β-malic acid) block, and PCL is a hydrophobic bioresorbable poly(ε-caprolactone) arm. Each constitutive arm was prepared by ring-opening polymerization. A double-headed PEO macroinitiator [PEO-(OH)-COO - K + ] was first prepared by selective hydrolysis of the α-lactone (2-oxepanone) end group of PEO chains end-capped by a ω-methoxy group. The anionic polymerization of benzyl β-malolactonate (MLABz) was selectively initiated by the α-potassium carboxylate end group of PEO in the presence of 18-crown-6 ether. The polymerization of ε-caprolactone (ε-CL) was initiated by the hydroxyl group left at the junction of the two blocks of the as-prepared PEO- b -PMLABz diblock copolymer, in the presence of tin(II) bis(2-ethylhexanoate) (Sn(Oct) 2 ). The macroinitiator, the intermediate diblock, and the final miktoarm star-shaped copolymer were analyzed by 1 H NMR spectroscopy and size exclusion chromatography.