Synthesis of macrocyclic molecular brushes with amphiphilic block copolymers as side chains

Macrocyclic molecular brushes c‐PHEMA‐g‐(PS‐b‐PEO) consisting of macrocyclic poly(2‐hydroxylethyl methacrylate) (c‐PHEMA) as backbone and polystyrene‐b‐poly(ethylene oxide) (PS‐b‐PEO) amphiphilic block copolymers as side chains were synthesized by the combination of atom transfer radical polymerization (ATRP), click chemistry, and single‐electron transfer nitroxide radical coupling (SET‐NRC). First, a linear α‐alkyne‐ω‐azido heterodifunctional PHEMA (l‐HC?C‐PHEMA‐N₃) was prepared by ATRP of HEMA using 3‐(trimethylsilyl)propargyl 2‐bromoisobutyrate as initiator, and then chlorine end groups were transformed to ? N₃ group by nucleophilic substitution reaction in DMF in the presence of an excess of NaN₃. The 3‐trimethylsilyl groups could be removed in the presence of tetrabutylammonium fluoride, and the product was cyclized by “click” chemistry in high dilution conditions. The hydroxyl groups on c‐PHEMA were transferred into bromine groups by esterification with 2‐bromoisobutyryl bromide and then initiate the ATRP of styrene. The formed macrocyclic molecular brushes c‐PHEMA‐g‐PS were coupled with the TEMPO‐PEO to afford the target macrocyclic molecular brushes c‐PHEMA‐g‐(PS‐b‐PEO) by SET‐NRC, and the efficiency is as high as 80～85%. All of the intermediates and final product were characterized with ¹H NMR, Fourier transform infrared (FTIR), and gel permeation chromatography in details © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011