Synthesis and Self-Assembly of Coil−Rod Double Hydrophilic Diblock Copolymer with Dually Responsive Asymmetric Centipede-Shaped Polymer Brush as the Rod Segment

Abstract

We report on the synthesis and self-assembly of well-defined coil−rod double hydrophilic diblock copolymer with pH- and thermo-responsive asymmetric centipede-shaped polymer brush as the rod segment via a combination of atom transfer radical polymerization (ATRP) and click chemistry (Schemes and ). At first, poly(ethylene oxide)-b-poly(glycidyl methacrylate), PEO-b-PGMA, was prepared by ATRP using PEO-based macroinitiator. The ring-opening of pendent epoxide moieties in PEO-b-PGMA with NaN3 followed by esterification with 2-bromoisobutyryl bromide afforded multifunctional PEO-b-[PGMA-(N 3)(Br)] bearing one azide and one bromine moieties on each monomer repeating unit of PGMA. The subsequent ATRP of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) using PEO-b-[PGMA-(N 3)(Br)] as the macroinitiator yielded PEO-b-[PGMA-g-(N 3)(PMEO2MA)] coil−brush diblock copolymer possessing one residual azide moiety at each grafting site. Finally, the target coil−rod diblock copolymer with asymmetric centipede-shaped polymer brush as the rod segment, PEO-b-[PGMA-g-(PDEA)(PMEO2MA)], was obtained via the click reaction of PEO-b-[PGMA-g-(N 3)(PMEO2MA)] with an excess of alkynyl-terminated poly(2-(diethylamino)ethyl methacrylate) (alkynyl-PDEA). All the intermediate and final products were characterized by 1H NMR, Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC). Atomic force microscopy (AFM) analysis revealed that PEO-b-[PGMA-g-(PDEA)(PMEO2MA)] coil−rod diblock unimer chains adopt a wormlike conformation in aqueous solution at pH 4 and room temperature. Possessing pH-responsive PDEA and thermo-responsive PMEO2MA grafts arranged in an asymmetric centipede manner within the rod segment, PEO-b-[PGMA-g-(PDEA)(PMEO2MA)] self-assembles into two types spherical aggregates in aqueous solution, depending on solution pH and temperatures. The multiresponsive switching between wormlike unimers and two types of micellar aggregates were characterized by temperature-dependent optical transmittance, dynamic laser light scattering (LLS), AFM, and transmission electron microscopy (TEM).

Synthesis and Self‐Assembly of New Double‐Crystalline Amphiphilic Polyethylene‐block‐Poly[oligo(ethylene glycol) Methyl Ether Methacrylate] Coil‐Brush Diblock Copolymer

“…Ambient temperature 1 H NMR (300 MHz) and 13 C NMR (75 MHz) spectra were recorded in CDCl 3 on a Varian Unity Inova 300 spectrometer and high temperature 13 C NMR (125 MHz) were performed on an INOVA 500 MHz spectrometer at 120 8C. Molecular weight and molecular weight distribution (M w =M n ) were determined by gel permeation chromatography (GPC) against narrow molecular weight distribution polystyrene standards on a Waters 2414 refractive index detector at ambient temperature with THF as solvent or a Water 150 8C at 135 8C with 1,2,4-trichlorobenzene as solvent.…”

“…[1][2][3][4][5][6][7][8][9] The coil-brush block copolymers in selective solvents can self-assemble into a variety of regular nanostructures, including spherical, [7,[10][11][12][13] hexagonal, [14] cylindrical, [15,16] vesicle, [17,18] and lamellar morphologies. [19] In order to investigate the self-assembly of coil-brush block copolymer, the preparation of a well-defined block copolymer is crucial.…”

“…[21] In another approach, the coil-brush block copolymers can be prepared via grafting-through, grafting-from, and grafting-onto techniques. Starting from macroinitiators with initiating sites distributed on each monomer repeating units, the recent boom of controlled polymerization techniques, such as ring-opening polymerization (ROP), [22] nitroxide-mediated polymerization (NMP), [23] atom transfer radical polymerization (ATRP), [13] reversible addition-fragmentation chain transfer (RAFT) polymerization, [24] and single-electron-transfer living radical polymerization (SET-LRP) [25] have rendered the graftingfrom approach more prevailing. Recently, click chemistry has been extensively used in polymer chemistry due to the high efficiency and technical simplicity of the reaction.…”

“…[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] Therefore, block copolymer brushes can also be synthesized by the click coupling reaction between block copolymer precursors, which possess clickable functionality on each monomer repeating units, and end-clickable-functionalized polymer chains. [13,42] On the other hand, one can prepare coil-brush block copolymers by coupling coil linear polymer chains and polymer brush chains end-terminated with suitable reactive groups. [43,44] To the best of our knowledge, the synthesis and selfassembly of coil-brush block copolymers with a linear crystalline polyethylene (PE) as one of the building block have not been reported.…”

Synthesis and self-assembly behavior of amphiphilic methyl α-D-glucopyranoside-centered copolymers

“…The grafting reactions via epoxy groups in the short PGMA segment in block copolymers were achieved with silanol functionality of silica nanoparticles [11], or aminosililated quartz wafer surfaces [12]. The macroinitiators based on PGMA after modifications contained one bromine and hydroxyl group [13,14] or an azide group [15] at every unit of the polymer, which were then selectively used in a polymerization or "click" reaction yielding the asymmetric centipede-like polymer brushes.…”