Synthesis of arborescent polystyrene by click grafting

A method was developed for the synthesis of arborescent polystyrene by click coupling. Acetylene functionalities were introduced on linear polystyrene (M-n = 5300 g/mol, M-w/M-n = 1.05) by acetylation and reaction with potassium hydroxide, 18-crown-6 and propargyl bromide in toluene. Polymerization of styrene with 6-tert-butyldimethylsiloxyhexyllithium yielded polystyrene (M-n = 5200 g/mol, M-w/M-n = 1.09) with a protected hydroxyl chain end. Deprotection, followed by conversions to tosyl and azide functionalities, provided the side chain material. Coupling with CuBr and N,N,N ',N '',N ''-pentamethyldiethylenetriamine proceeded in up to 94% yield. Repetition of the grafting cycles led to well-defined (M-w/M-n <= 1.1) polymers of generations G1 and G2 in 84% and 60% yield, respectively, with M-n and branching functionalities reaching 2.8 x 10(6) g/mol and 460, respectively, for the G2 polymer. Coupling longer (M-n = 45,000 g/mol) side chains with acetylene-functionalized substrates was also examined. For a linear substrate, a G0 polymer with M-n = 4.6 x 10(5) g/mol and M-w/M-n = 1.10 was obtained in 87% yield; coupling with the G0 (M-n = 52,000 g/mol) substrate produced a G1 polymer (M-n = 1.4x10(6) g/mol, M-w/M-n = 1.38) in 28% yield. The complementary approach using azide-functionalized substrates and acetylene-terminated side chains was also investigated, but proceeded in lower yield. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019