Cyclic and multiblock polystyrene-block-polyisoprene copolymers by combining anionic polymerization and azide/alkyne "click" chemistry

An α,ω-heterotelechelic block copolymer of polystyrene (PS) and polyisoprene (PI), α-acetylene-ω-azido-PS-b-PI, with M_n = 18 900 and PDI = 1.05, was synthesized by (a) sequential anionic polymerization of styrene and isoprene with 5-triethylsilyl-4-pentynyllithium (TESPLi) as initiator to afford α-(TES-acetylene)-ω-lithium-PS-b-PI, (b) reaction of the living heterofunctionalized copolymer with 1,4-dibromobutane and sodium azide to give α-(TES-acetylene)-ω- azido-PS-b-PI, and (c) deprotection of the acetylene group to afford the final product α-acetylene-ω-azido-PS-b-PI. This α,ω- heterotelechelic block copolymer with "clickable" groups, in the presence of CuBr and N,N,N′,N′′,N′′- pentamethyldiethylenetriamine, led to cyclic block copolymer in dilute solution (lower than the equilibrium concentration <6 × 10^-5 g/mL), whereas in concentrated solutions (5.3 × 10^-2 g/mL) gave multiblock copolymers.