Synthesis of Well-Defined Silica and Pd/Silica Nanotubes through a Surface Sol−Gel Process on a Self-Assembled Chelate Block Copolymer

The synthesis of well-defined silica nanotubes and Pd nanoparticle-decorated silica nanotubes is reported. The synthesis of silica nanotubes involves (1) formation of a 1-D template of the core−corona threadlike micelles through self-assembly of poly(ethylene glycol)-block-poly(4-vinylpyridine) in water, (2) a directed surface sol−gel process of tetraethylorthosilicate (TEOS) on the template of the threadlike micelles, and (3) calcination to remove the template. Because of the inherently pendent catalyst sites of the poly(4-vinylpyridine) block on the threadlike micelles, the surface sol−gel process is directed onto the template, and therefore, formation of irregular silica aggregates is avoided. Following the proposed method, well-defined silica nanotubes with thicknesses ranging from 3 to 17 nm are produced by changing the weight ratio of TEOS/micelles. Also benefiting from the chelate poly(4-vinylpyridine) block, Pd nanoparticles are introduced into the cavum of silica nanotubes initially through coordination between the poly(4-vinylpyridine) block with the Pd precursor, followed by reduction with NaBH4 aqueous solution

Yolk−Shell Catalyst of Single Au Nanoparticle Encapsulated within Hollow Mesoporous Silica Microspheres

Synthesis and catalysis of yolk−shell microspheres containing a single Au nanoparticle core and a mesoporous shell of hollow mesoporous silica microspheres (HMSM) are reported. This synthesis employs polystyrene-co-poly(4-vinylpyridine) microspheres as both template to fabricate the HMSM shell through sol−gel process and scaffold to immobilize the Au nanoparticle. Since the single Au nanoparticle core is supernatant within the inert HMSM shell, the yolk−shell catalyst has minimum support effect and is a promising model to explore the origin of Au catalysis. Catalyzed reduction of 4-nitrophenol with NaBH4 demonstrates size-dependent induction or activation and size-dependent activity of the Au nanoparticle core of the yolk−shell catalyst

Concise Synthesis of Photoresponsive Polyureas Containing Bridged Azobenzenes as Visible-Light-Driven Actuators and Reversible Photopatterning

Linear photoresponsive polyurea of PbAzo containing bridged-azobenzene moieties in backbone was synthesized via polyaddition reaction between hexamethylene diisocyanate and <i>cis</i>-3,3′-diamino ethylene-bridged azobenzene. The bridged-azobenzene moieties endow the PbAzo polyurea advantages of visible-light-driven isomerization and fast and powerful photoresponse. Under irradiation with 405 nm blue light, stable <i>cis</i>-PbAzo converts into metastable <i>trans</i>-PbAzo accompanying the amorphous-to-crystalline transition and the yellow-to-red color change via <i>cis</i>-to-<i>trans</i> isomerization. With further illumination with 532 nm green light, <i>trans</i>-to-<i>cis</i> isomerization reversibly takes place. This photoresponsive polyurea is used in photopatterning, in which patterns can be reversibly written or erased alternatively by 405 nm blue light and 532 nm green light or heating. Besides, the polyurea film can act as qualified visible-light-driven actuators. Under irradiation with 405 nm blue light, it initially bends away the light source with the bending angle above 110 deg in several seconds, and then it recovers to its initial state with no attenuation under irradiation with 532 nm green light. Our photoresponsive polyurea is different from photoresponsive polymers including planar azobenzene moieties, and this polyurea is expected to be promising for smart materials

Pd-Catalyzed C−C Cross-Coupling Reactions within a Thermoresponsive and pH-Responsive and Chelating Polymeric Hydrogel

A porous, thermoresponsive and pH-responsive, and chelating hydrogel of poly(N-isopropylacrylamide)-co-poly[2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxypropyl ester] (PNIPAM-co-PMACHE) is proposed as both a reaction medium and the Pd catalyst support for organic synthesis. Organic synthesis within the PNIPAM-co-PMACHE hydrogel has three merits. First, organic reactions such as Suzuki and Heck reactions within the hydrogel can be accelerated due to the enriched Pd catalyst and reactants within the hydrogel by the reversible deswelling/swelling. Second, organic synthesis within the PNIPAM-co-PMACHE hydrogel, which holds about ∼300 times of water and is similar to the environmentally benign reaction medium of water, can be performed efficiently without surfactant or cosolvent being added. Third, the PNIPAM-co-PMACHE hydrogel itself and the therein-immobilized Pd catalyst can be easily recycled since the hydrogel/Pd composite can reversibly swell/deswell

Thermoresponsive Micellization of Poly(ethylene glycol)-<i>b</i>-poly(<i>N</i>-isopropylacrylamide) in Water

Thermoresponsive micellization of poly(ethylene glycol)-b-poly(N-isopropylacrylamide) (PEG110-b-PNIPAM44) in water is studied by static light scattering and dynamic light scattering. The critical aggregation temperature of PEG110-b-PNIPAM44 is a little higher than homopolymer PNIPAM, and it depends on the block copolymer concentration, which increases from 33.7 to 38.4°C when the copolymer concentration decreases from 2.0 to 0.20 mg/mL. Above the critical aggregation temperature, thermoresponsive micellization occurs, and the resultant spherical micelles consist of a PNIPAM core and a PEG shell. The block copolymer concentration exerts a strong influence on the size and structure of the resultant micelles. Micellization of PEG110-b-PNIPAM44 at higher copolymer concentration favors formation of narrowly distributed, small, and dense micelles, while large, loose micelles or micellar clusters form at lower block copolymer concentration

Hybrid Nanoscale Vesicles of Polyhedral Oligomeric Silsesquioxane-Based Star Block Copolymers for Thermal Insulation Applications

Organic–inorganic hybrid vesicles of the polyhedral oligomeric silsesquioxane (POSS)-based star block copolymer of poly­(N-isopropylacrylamide)-block-polystyrene [POSS-(PNIPAM-b-PS)8] were synthesized by polymerization-induced self-assembly via reversible addition–fragmentation chain transfer (RAFT) polymerization employing a POSS-based macromolecular chain transfer agent. The average diameter, the membrane thickness, and the cavity volume fraction of the POSS-(PNIPAM-b-PS)8 vesicles are 212 nm, 21 nm, and 52%, respectively. The POSS-(PNIPAM-b-PS)8 vesicles exhibit good thermal stability and have 12% higher Young’s modulus than the vesicles of linear block copolymer counterparts. Due to the high mechanical strength, the POSS-(PNIPAM-b-PS)8 vesicles can keep structural integrity in the dried state. The coating of the POSS-(PNIPAM-b-PS)8 vesicles is prepared by casting the dispersion of the star block copolymer vesicles at room temperature, and then, its application as a thermal insulation coating is investigated. It is found that the POSS-(PNIPAM-b-PS)8 vesicles can be used as qualified thermal insulation materials with the thermal conductivity as low as 0.131 W/m·K

Microreactor of Pd Nanoparticles Immobilized Hollow Microspheres for Catalytic Hydrodechlorination of Chlorophenols in Water

A microreactor of Pd nanoparticles immobilized shell-corona hollow microspheres of poly[styrene-co-2-(acetoacetoxy) ethyl methacrylate-co-acrylamide] has been designed for catalytic hydrodechlorination (HDC) of chlorophenols in the sole solvent of water. The strategy of the combined use of the shell-corona hollow microspheres as microcapsule and catalyst scaffold endues the microreactor several advantages. First, the microreactor can be dispersed in the sole solvent of water and acts as a quasi-homogeneous catalyst for catalytic HDC of chlorophenols. Second, the reactant of chlorophenols can be highly concentrated within the hollow microspheres of the microreactor in the sole solvent of water. Third, the resultant product of phenol can be favorably excreted off the microreactor into water because of the polar difference between the reactant of chlorophenols and the product of phenol. Ascribed to the combined advantages, catalytic HDC of chlorophenols can be performed efficiently within the microreactor in the sole solvent of water at room temperature under atmosphere pressure

Suzuki Reaction within the Core−Corona Nanoreactor of Poly(<i>N</i>-isopropylacrylamide)-Grafted Pd Nanoparticle in Water

A nanoreactor of poly(N-isopropylacrylamide)-grafted Pd nanoparticle (Pd@PNIPAM) is proposed for the Suzuki reaction performed in the sole solvent of water. The Pd@PNIPAM nanoparticle has a core of Pd nanoparticle and a corona of poly(N-isopropylacrylamide) brushes. The Pd@PNIPAM nanoparticle can act as a nanoreactor for the Suzuki reaction since the grafted poly(N-isopropylacrylamide) brushes provide a nanoenvironment for guest molecules. Both hydrophilic and hydrophobic reactants can be enriched in the nanoreactor of Pd@PNIPAM, and therefore the Suzuki reaction within the nanoreactor is performed in water at room temperature or above the phase-transition temperature of the corona-forming brushes of poly(N-isopropylacrylamide). Besides, the nanoreactor of Pd@PNIPAM can be recycled due to the reversible phase-transition of the poly(N-isopropylacrylamide) brushes