Synthesis of a sun-shaped amphiphilic copolymer consisting of a cyclic perfluorocyclobutyl aryl ether-based backbone and lateral PMAA side chains

A novel amphiphilic sun-shaped copolymer, c-PMBTFVB-g-PMAA (MBTFVB: 2-methyl-1,4-bistrifluorovinyloxybenzene, MAA: methacrylic acid) containing a cyclic perfluorocyclobutyl (PFCB) aryl ether-based backbone and PMAA lateral side chains with narrow molecular weight distribution (M-w/M-n <= 1.38), was synthesized via the site transformation strategy. First, a PMBTFVB linear precursor was prepared by thermal step-growth cycloaddition polymerization of MBTFVB trifluorovinyl monomer. After the end functionalization of the linear precursor with alkyne, Glaser coupling reaction was performed to produce c-PMBTFVB cyclic homopolymer. The pendant methyls on PFCB aryl ether-based backbone were then converted to Br-containing ATRP initiating groups by a mono-bromination reaction with N-bromosuccinimide (NBS) and benzoyl peroxide (BPO) to give c-PMBTFVB-Br cyclic macroinitiator without affecting the main chain, where the density of ATRP initiation groups could be tuned from 33% to 58% by varying the feeding ratio of NBS to the pendant methyl. Subsequently, c-PMBTFVB-g-PMAA sun-shaped amphiphilic copolymers with hydrophilic PMAA side chains were synthesized by ATRP of tert-butyl methacrylate (tBMA) initiated by c-PMBTFVB-Br, followed by the selective hydrolysis of hydrophobic PtBMA segment into hydrophilic PMAA segment using CF3COOH. The obtained c-PMBTFVB cyclic homopolymer and its precursor were well characterized by GPC, NMR, and DSC and all the observations indicated a high efficiency of the intra-macromolecular cyclization via Glaser coupling reaction. The critical micelle concentrations of the obtained amphiphilic copolymers were determined by fluorescence probe technique and the morphologies of the formed micelles were investigated by TEM.