Controlled synthesis of an ABC miktoarm star-shaped copolymer by sequential ring-opening polymerization of ethylene oxide, benzyl b-malolactonate and e-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 ß-malolactonate) arm precursor of a pH-sensitive bioresorbable poly(ß-malic acid) block, and PCL is a hydrophobic bioresorbable poly(e-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 a-lactone (2-oxepanone) end group of PEO chains end-capped by a ?-methoxy group. The anionic polymerization of benzyl ß-malolactonate (MLABz) was selectively initiated by the a-potassium carboxylate end group of PEO in the presence of 18-crown-6 ether. The polymerization of e-caprolactone (e-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 1H NMR spectroscopy and size exclusion chromatography.