ROMP-Derived Pyridylborate Block Copolymers: Self-Assembly, pH-Responsive Properties, and Metal-Containing Nanostructures

Abstract

The functionalization of organic polymers with polydentate ligands offers opportunities in areas ranging from supported catalysts to materials with desirable magnetic, redox-active, stimuli-responsive, and self-healing properties. Herein, we present the synthesis and self-assembly of tris­(2-pyridyl)­borate (Tpyb)-functionalized homo and block copolymers, prepared via ring-opening metathesis polymerization (ROMP) of (bicyclo[2.2.1]­hept-5-en-2-yl)-4-phenyl) (pyridin-1-ium-2-yl)­di­(pyridin-2-yl)­borate (M1) and dimethyl-7-oxabicyclo[2.2.1]­hept-5-ene-exo,exo-2,3-dicarboxylate (M2) using Grubbs third-generation catalyst. Controlled polymerization was confirmed by gel permeation chromatography (GPC; also referred to as size exclusion chromatography, SEC) and multinuclear NMR spectroscopy. The solution self-assembly in block-selective solvents (MeOH, THF) was investigated by dynamic light scattering (DLS), scanning electron microscopy (SEM), scanning tunneling electron microscopy (STEM), and transmission electron microscopy (TEM), and the microphase separation in a thin film was imaged by atomic force microscopy (AFM). Hydrolysis of the ester-substituted oxanorbornene block with NaOH led to a new copolymer with carboxylate functionalities that can be dispersed in water. The latter displays multiresponsive properties as each of the individual blocks can be reversibly switched between hydrophobic and hydrophilic states by simple adjustment of pH. Cross-linking of the block copolymer aggregates via metal ion complexation was accomplished, and the feasibility of metal ion exchange was demonstrated by energy-dispersive X-ray spectroscopy (EDX).

Synthesis and Characterization of Phosphorus- and Carborane-Containing Polyoxanorbornene Block Copolymers

“…Exploiting the precise control over the polymer chains, as offered by ROMP, the obtained block copolymers can undergo self-assembly via switching capabilities between hydrophobic and hydrophilic states [11,18,19,20,21,22]. For example, multiresponsive pH-dependent self-assembly and further metal ion complexation was explored via the exchange of Cu(II) with Fe(II) ions in the polymer networks [23].…”

One‐Step Ring Opening Metathesis Block‐Like Copolymers and their Compositional Analysis by a Novel Retardation Technique

“…Grubbs first (G1, dichloro(benzylidene)bis(tricyclohexylphosphine) ruthenium(II)) and third (G3, dichloro[1,3bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene](benzylidene)bis(3-bromopyridine) ruthenium(II)) generation metathesis catalysts are most frequently employed in polymer synthesis due to their high initiation to propagation rate ratios which ensure narrow molecular weight dispersities. [29,30] There are numerous reports of ROMP-based block copolymer syntheses by sequential monomer addition using ruthenium- [31][32][33] and molybdenum-based metathesis catalysts. [34][35][36][37][38] However, reports on one-step block-like copolymer syntheses by ROMP are scarce.…”

Controlling the aggregation and assembly of boron‐containing molecular and polymeric materials

“…[108] Jäkle and co-workers have developed a wide range of block copolymers containing pendant boron moieties through controlled free-radical polymerization, and investigated their nanostructures. [22,[109][110][111][112][113][114] Among them are amphiphilic block copolymers PB10 with well-defined chain architectures that consist of luminescent triarylborane Lewis acidfunctionalized styrene and N-isopropylacrylamide (NIPAM) (Figure 4B). [115] In a mixture of DMF/THF = 99/1, these strongly blue fluorescent block copolymers formed micellar aggregates as confirmed by dynamic light scattering measurements and transmission electron microscopy.…”