pH-Responsive Supramolecular Self-Assembly of Well-Defined ZwitterionicABC Miktoarm Star Terpolymers

摘要

We report the first example of the synthesis and pH-responsive supramolecular self-assembly of doublehydrophilic ABC miktoarm star terpolymers. Well-defined ABC miktoarm star terpolymers consisting ofpoly(ethylene glycol), poly(tert-butyl methacrylate), and poly(2-(diethylamino)ethyl methacrylate) arms [PEG(-b-PtBMA)-b-PDEA] were synthesized via the combination of consecutive click reactions and atom transferradical polymerization (ATRP), starting from a trifunctional core molecule, 1-azido-3-chloro-2-propanol(ACP). The click reaction of monoalkynyl-terminated PEG with an excess of ACP afforded difunctional PEGbearing a chlorine and a secondary hydroxyl moiety at the chain end, PEG_(113)(-Cl)-OH (1). After azidation withNaN_3, PEG-based macroinitiator PEG_(113)(-N_3)-Br (3) was prepared by the esterification of 113)(-OH 2)with 2-bromoisobutyryl bromide and then employed in the ATRP of tert-butyl methacrylate (tBMA). Theobtained PEG(-N_3)-b-PtBMA copolymers (4) possessed an azido moiety at the diblock junction point. Thepreparation of PEG(-b-PtBMA)-b-PDEA miktoarm star terpolymers was then achieved via the click reaction of4 with an excess of monoalkynyl-terminated PDEA. The obtained miktoarm star terpolymers were successfullyconverted into PEG(-b-PMAA)-b-PDEA, where PMAA is poly(methacrylic acid). In aqueous solution, PEG(-b-PMAA)-b-PDEA zwitterionic ABC miktoarm star terpolymers can self-assemble into three types of micellaraggregates by simply adjusting solution pH at room temperature. Above pH 8, PDEA-core micelles stabilized byPEG/ionized PMAA hybrid coronas were formed due to the insolubility of PDEA block. In the range of pH 5-7,micelles possessing polyion complex cores formed as a result of charge compensation between partially ionizedPMAA and partially protonated PDEA sequences. At pH < 4, hydrogen bonding interactions between fullyprotonated PMAA and PEG led to the formation of another type of micellar aggregates possessing hydrogen-bonded complex cores stabilized by protonated PDEA coronas. The fully reversible pH-responsive formation ofthree types of aggregates were characterized by ~1H NMR, dynamic and static laser light scattering (LLS), andtransmission electron microscopy (TEM).