Star Block Copolymers and Hexafullerene Stars via Derivatization of Star-Shaped Polystyrenes

The end-functionalization of hexaarm star-shaped polystyrene (PS), prepared via "living" cationic polymerization, by organosilicon compounds was investigated. The presence of a sec-chlorine atom at each branch end was first confirmed by ¹H NMR. After activation of these chain ends by TiCl₄, both allylic and azido groups were introduced through the use of their trimethylsilyl derivatives (allyltrimethylsilane and trimethylsilyl azide, respectively), particularly taking advantage of the high affinity of silicon compounds toward electrophilic reagents. These end-standing allyl and azide functions on the hexaarm PS stars were then transformed into hydroxyl and amino groups with use of classical organic chemistry reactions. PS stars carrying six fullerenes on their periphery were also generated from hexaazido star samples. The presence of these six C₆₀ entities was confirmed by miscellaneous characterization methods, including ¹H NMR, size-exclusion chromatography, thermal gravimetry, and cyclic voltammetry. Besides the synthesis of these ω-functionalized stars, PS₆-b-PEO₆ star block copolymers were also prepared with use of the hexahydroxy samples as macroinitiators of ethylene oxide polymerization.