Cyclic and Multiblock Polystyrene-block-polyisoprene Copolymers by Combining Anionic Polymerization and Azide/Alkyne "Click" Chemistry

An alpha,omega-heterotelechelic block copolymer of polystyrene (PS) and polyisoprene (P1), alpha-acetylene-omega-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 S-triethylsilyI-4-pentynyllithium (TESPLi) as initiator to afford alpha-(TES-acetylene)-omega-lithium-PS-b-PI, (b) reaction of the living heterofunctionalized copolymer with 1,4-dibromobutane and sodium azide to give alpha-(TES-acetylene)-omega-azido-PS-b-PI, and (c) deprotection of the acetylene group to afford the final product alpha-acetylene-omega-azido-PS-b-PI. This alpha,omega-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 x 10(-5) g/ml,), whereas in concentrated solutions (5.3 x 10(-2) g/mL) gave multiblock copolymers.