Synthesis of 3‐Arm Star Block Copolymers by Combination of “Core‐First” and “Coupling‐Onto” Methods Using ATRP and Click Reactions

Abstract Three‐arm star block copolymers were successfully synthesized by combination of “core‐first” and “coupling‐onto” strategies. First, polystyrene 3‐arm star polymers (PS‐Br) 3 with high bromine chain‐end functionality were synthesized by atom transfer radical polymerization (ATRP) using the core‐first method. After complete transformation of the bromo groups to azido groups by nucleophilic substitution with sodium azide, the product (PS‐N 3 ) 3 was used for click reactions with alkyne‐terminated poly(ethylene oxide) chains (PEO‐alkyne) and produced 3‐arm star block copolymers (PS‐ b ‐PEO) 3 via the coupling‐onto method. The efficiency of the coupling reaction was influenced by the preservation of chain‐end functionalities in both (PS‐N 3 ) 3 and PEO‐alkyne precursors. The azido functionality in the (PS‐N 3 ) 3 star precursors was determined as high as 97% by gradient polymer elution chromatography (GPEC) analysis of the coupling product between (PS‐N 3 ) 3 and propargyl alcohol. During the coupling reactions between (PS‐N 3 ) 3 and PEO‐alkyne, the functionality of PEO‐alkyne was ca. 100%. In the final coupling product, the molar fraction of the targeted (PS‐ b ‐PEO) 3 star block polymers containing three block arms was ca. 85% and the fraction of the star polymers with two block arms and one homopolymer arm, (PS)‐(PS‐ b ‐PEO) 2 , was ca. 11%. magnified image