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

摘要

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-N_3) 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