Synthesis of arborescent polystyrene by “click” grafting

Abstract

ABSTRACTA method was developed for the synthesis of arborescent polystyrene by “click” coupling. Acetylene functionalities were introduced on linear polystyrene (Mn = 5300 g/mol, Mw/Mn = 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 (Mn = 5200 g/mol, Mw/Mn = 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 (Mw/Mn ≤ 1.1) polymers of generations G1 and G2 in 84% and 60% yield, respectively, with Mn and branching functionalities reaching 2.8 × 106 g/mol and 460, respectively, for the G2 polymer. Coupling longer (Mn = 45,000 g/mol) side chains with acetylene‐functionalized substrates was also examined. For a linear substrate, a G0 polymer with Mn = 4.6 × 105 g/mol and Mw/Mn = 1.10 was obtained in 87% yield; coupling with the G0 (Mn = 52,000 g/mol) substrate produced a G1 polymer (Mn = 1.4×106 g/mol, Mw/Mn = 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. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1730–1740