Synthesis and characterization of novel resorcinarene- centered amphiphilic star-block copolymers consisting of eight ABA triblock arms by combination of ROP, ATRP, and click chemistry

Novel amphiphilic eight-arm star triblock copolymers, star poly(ε-capro- lactone)-block-poly(acrylic acid)-block-poly(ε- caprolactone)s (SPCL-PAA-PCL) with resorcinarene as core moiety were prepared by combination of ROP, ATRP, and "click" reaction strategy. First, the hydroxyl end groups of the predefined eight-arm SPCLs synthesized by ROP were converted to 2-bromoesters which permitted ATRP of tert-butyl acrylate (tBA) to form star diblock copolymers: SPCL-PtBA. Next, the bromide end groups of SPCL-PtBA were quantitatively converted to terminal azides by NaN₃, which were combined with presynthesized alkyne-terminated poly(ε-capro- lactone) (A-PCL) in the presence of Cu(I)/N,N,N′,N″,N″- pentamethyldiethylenetri- amine in DMF to give the star triblock copolymers: SPCL-PtBA-PCL. ¹H NMR, FTIR, and SEC analyses confirmed the expected star triblock architecture. The hydrolysis of tert-butyl ester groups of the poly(tert-butyl acrylate) blocks gave the amphiphilic star triblock copolymers: SPCL-PAA-PCL. These amphiphilic star tri-block copolymers could self-assemble into spherical micelles in aqueous solution with the particle size ranging from 20 to 60 nm. Their micellization behaviors were characterized by dynamic light scattering and transmission electron microscopy.