Dendritic Amphiphile Mediated One-Pot Preparation of 3D Pt Nanoparticles-Decorated PolyHIPE as a Durable and Well-Recyclable Catalyst

Trace Thiol Moieties in the Ligand Layer Induce Superior Catalytic Gold Nanoclusters

We here show that the typical poison of thiols, if below a certain level, promotes rather than suppresses the catalytic activity of gold nanoclusters (AuNCs). A few thiol groups functionalized hyperbranched polyethylenimine (PEI, Mn = 2000 Da) patched on a mesoporous polymeric bead aid the direct synthesis of AuNCs. The nucleation efficiency of AuNC is 93-fold favored at a level of 2 thiols per PEI (0.04 equiv of the amino units) than that by neat PEI, and AuNCs (1.3 nm) are obtained up to a gold load of 6.3% on the support. Unexpectedly, the catalytic activity of AuNCs is favored by the thiol up to 2 thiols per PEI, as evaluated from the surface-normalized rate constant of the model reaction of 4-nitrophenol-reduction. The catalytic promotion by thiols probably stems from optimized electron density on AuNC. If the residual NH groups of PEI were further fully treated with glycidyltrimethylammonium chloride, the catalytic activity is again enhanced, where the accelerated mass transfer is responsible for the promotion. Overall, the catalytic activity reaches an unprecedented value (metal-normalized rate constant kc = 29.4 L mmol-1 s-1 and turnover frequency = 1623 h-1, as evaluated with the model reaction of 4-nitrophenol reduction) ever reported for supported AuNCs. Our results suggest that orthogonal ligand optimization is an effective manner of triggering the release of the catalytic potential of AuNCs, among which thiol is unique.

Customizing a Hyperbranched Ligand Confers Supported Platinum Nanoclusters with Unexpected Catalytic Activity toward the Reduction of 4-Nitrophenol

We here show that a dendritic molecule combined with ligand merit confers supported platinum nanoclusters (PtNCs) with unprecedented catalytic performance. Branched polyethylenimine (PEI, Mn = 2000 D) patched on a porous bead is modified with 2-(diphenylphosphino)benzaldehyde (dppb) before being used to mediate a platinum nanoparticle/nanocluster (Pt0). The catalytic activity of Pt0 toward the reduction of 4-nitrophenol (4-NP) is evaluated from the parameter of Pt-normalized rate constant (kc). Optimization of the dppb level along with transformation of the PEI hydrogens into diol or trimethylammonium groups imparts supported Pt0 unprecedented activity (kc = 19.2 L mmol-1 s-1 and turnover frequency (TOF) = 1041 h-1). The supported Pt0 at an extremely low dosage of 0.1 ppm promotes 98% conversion of 4-NP within minutes and is well recyclable. The striking catalytic activity is attributed to the combination of orthogonal ligand properties such as weak ligand nature, catalyst-activating ability, excellent substrate affinity, and effect on PtNC-size mediation of the ligand.

Photoresponsive Emulsion-Templated Porous Materials via Orthogonal Photoclick Chemistry

The functionalization of emulsion-templated porous polymers (polyHIPEs) utilizing modern and efficient chemistries is an important avenue for tailoring the properties of these scaffolds for specific and specialized applications. Herein, tetrazole photoclick chemistry is utilized for the efficient functionalization of polyHIPEs synthesized from various monomer systems and polymerization chemistries. Using both radical polymerization and thiol-ene polymerization, polyHIPEs with well-defined, interconnected open-cell morphologies are synthesized with tetrazole concentrations ranging from 0 to 5 w/v %, with the pore diameters ranging from 3 to 24 μm. Analyzed by fluorescence spectroscopy, FTIR spectroscopy, and confocal microscopy, spatially controlled functionalization to generate photopatterned fluorescent polyHIPEs is demonstrated via the reaction with residual acrylate and thiol groups. In addition, the scaffolds can be readily functionalized with external dipolarophiles such as acrylates to incorporate a functionality onto the polyHIPE surface. With many functional tetrazoles also reported in the literature, a PEG-tetrazole is also used to explore the photoinduced functionalization of polyHIPEs possessing tunable ratios of thiol and acrylate groups, and the effect on fluorescence, wettability, and biocompatibility is analyzed. Overall, the reaction is shown to be a broadly applicable tool for polyHIPE functionalization with many avenues for further development toward specific applications.

Catalytic Neutralization of Water Pollutants Mediated by Dendritic Polymers

Radially polymerized dendritic compounds are nowadays an established polymer category next to their linear, branched, and cross-linked counterparts. Their uncommon tree-like architecture is characterized by adjustable internal cavities and external groups. They are therefore exceptional absorbents and this attainment of high concentrations in their interior renders them ideal reaction media. In this framework, they are applied in many environmentally benign implementations. One of the most important among them is water purification through pollutant decomposition. Simple and composite catalysts and photo-catalysts containing dendritic polymers and applied in water remediation will be discussed jointly with some unconventional solutions and prospects.

Flow-Through PolyHIPE Silver-Based Catalytic Reactor

Catalytic reactors performing continuously are an important step towards more efficient and controllable processes compared to the batch operation mode. For this purpose, homogenous high internal phase emulsion polymer materials with an immobilized silver catalyst were prepared and used as a continuous plug flow reactor. Porous material with epoxide groups was functionalized to bear aldehyde groups which were used to reduce silver ions using Tollens reagent. Investigation of various parameters revealed that the mass of deposited silver depends on the aldehyde concentration as well as the composition of Tollens reagent. Nanoparticles formed on the pore surface showed high crystallinity with a cuboctahedra crystal shape and highly uniform surface coverage. The example of the 4-nitrophenol catalytic reduction in a continuous process was studied and demonstrated to be dependent on the mass of deposited silver. Furthermore, productivity increased with the volumetric silver density and flow rate, and it was preserved during prolonged usage and storage.

Greener, Faster, Stronger: The Benefits of Deep Eutectic Solvents in Polymer and Materials Science

Deep eutectic solvents (DESs) represent an emergent class of green designer solvents that find numerous applications in different aspects of chemical synthesis. A particularly appealing aspect of DES systems is their simplicity of preparation, combined with inexpensive, readily available starting materials to yield solvents with appealing properties (negligible volatility, non-flammability and high solvation capacity). In the context of polymer science, DES systems not only offer an appealing route towards replacing hazardous volatile organic solvents (VOCs), but can serve multiple roles including those of solvent, monomer and templating agent-so called "polymerizable eutectics." In this review, we look at DES systems and polymerizable eutectics and their application in polymer materials synthesis, including various mechanisms of polymer formation, hydrogel design, porous monoliths, and molecularly imprinted polymers. We provide a comparative study of these systems alongside traditional synthetic approaches, highlighting not only the benefit of replacing VOCs from the perspective of environmental sustainability, but also the materials advantage with respect to mechanical and thermal properties of the polymers formed.

Dendritic Macrosurfactant Assembly for Physical Functionalization of HIPE-Templated Polymers

High-internal-phase emulsion-templated macroporous polymers (polyHIPEs) have attracted much interest, but their surface functionalization remains a primary concern. Thus, competitive surface functionalization via physical self-assembly of macrosurfactants was reviewed. Dendritic and diblock-copolymer macrosurfactants were tested, and the former appeared to be more topologically competitive in terms of solubility, viscosity, and versatility. In particular, hyperbranched polyethyleneimine (PEI) was transformed into dendritic PEI macrosurfactants through click-like N-alkylation with epoxy compounds. Free-standing PEI macrosurfactants were used as molecular nanocapsules for charge-selective guest encapsulation and robustly dictated the surface of a macroporous polymer through the HIPE technique, in which the macroporous polymer could act as a well-recoverable adsorbent. Metal nanoparticle-loaded PEI macrosurfactants could similarly lead to polyHIPE, whose surface was dictated by its catalytic component. Unlike conventional Pickering stabilizer, PEI macrosurfactant-based metal nanocomposite resulted in open-cellular polyHIPE, rendering the catalytic sites well accessible. The active amino groups on the polyHIPE could also be transformed into functional groups of aminopolycarboxylic acids, which could efficiently eliminate trace and heavy metal species in water.

Poly(vinylbenzyl chloride-co-divinyl benzene) polyHIPE monolith-supported o-hydroxynaphthaldehyde propylenediamine Schiff base ligand complex of copper(ii) ions as a catalyst for the epoxidation of cyclohexene

Poly(vinylbenzyl chloride-co-divinyl benzene)-based polyHIPE monoliths of different porosities were prepared using high-internal-phase emulsions (HIPEs) containing a fixed amount of vinylbenzyl chloride (VBC, 6.0 g, 0.0393 mol) and divinyl benzene (DVB 4.0 g, 0.0308 mol) as the oil phase and different volume ratios of aqueous calcium chloride as the internal phase. Span-80 (2.0 g (4.67 mmol))-stabilized HIPEs were polymerized at 60 °C using potassium persulfate (0.4 g, 1.48 mmol) as the initiator. Upon varying the volume ratio of aqueous calcium chloride from 80 to 90%, the prepared polyHIPE monoliths have shown significant variations in their surface morphology, specific surface area (SA), and pore volumes (V p) as confirmed by scanning electron microscopy (SEM) and a gas adsorption (BET) method. The prepared polyHIPE monoliths were anchored with o-hydroxynaphthaldehyde propylenediamine Schiff base ligand (HNPn) and then loaded with copper(ii) ions (HNPn-Cu) to act as a catalyst. The structural information of unsupported HNPn-Cu complexes was obtained by recording its FT-IR and UV-visible spectra. The amount of copper(ii) ions loaded onto HNPn ligand-anchored polyHIPE monoliths was determined by atomic absorption spectroscopic analysis. In comparison to unsupported HNPn-Cu catalyst, the polyHIPE monolith-supported HNPn-Cu catalyst has shown high catalytic activity (66.8%), product selectivity for epoxycyclohexane (ECH) (94.8%), high turn over number (0.028 mol mol-1 h-1) and low energy of activation (22.4 kJ mol-1) in the epoxidation of cyclohexene in the presence of hydrogen peroxide (H2O2) as an oxidant at 40 °C. The polyHIPE-supported HNPn-Cu catalyst also shows high reuse applications. Studies show that there is sufficient scope to develop polyHIPE monoliths with various properties for specific applications.

Polyimide-Based PolyHIPEs Prepared via Pickering High Internal Phase Emulsions

Pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) oligoimide particles and PMDA-ODA poly(amic acid) salt (PAAS) were synthesized and used as stabilizers to prepare oil-in-water Pickering high internal phase emulsions (HIPEs). The stability of the Pickering HIPEs was investigated by dispersion stability analysis. Polyimide-based polyHIPEs could be prepared through freeze-drying and subsequent thermal imidization of the Pickering HIPEs. The characteristics of the polyHIPEs, including their morphology, porosity, thermal decomposition temperature, and compression modulus, were investigated. The thermal decomposition temperature (T₁₀) of the polyHIPEs was very high (>530 °C), and their porosity was as high as 92%. The polyimide-based polyHIPEs have the potential to be used in high-temperature environments.

PDMS-Infused Poly(High Internal Phase Emulsion) Templates for the Construction of Slippery Liquid-Infused Porous Surfaces with Self-cleaning and Self-repairing Properties

Advanced liquid-repelling materials that resist both water-based and oil-based contaminants have significant applications in many fields. Herein, a novel protocol for the fabrication of a robust poly(high internal phase emulsion) (polyHIPE)-based slippery liquid-infused porous surface (SLIPS) system with combined self-repairing and self-cleaning properties is developed. Specifically, polystyrene-based polyHIPE (PS-HIPE) membranes with an interconnected porous structure were prepared from polymerization of the continuous oil phase in the water-in-oil HIPE templates. These polyHIPE membranes were used, for the first time, as porous substrates for loading low surface tension silicone oils as lubricating liquids for the fabrication of polyHIPE-based SLIPS membranes. These polyHIPE-based SLIPS membranes could easily repel both water- and oil-based contaminants (e.g., ink, milk, and coffee) with very low sliding angles (3.0 ? 1.3?) and could even repel solid contaminants (e.g., dust) upon washing with water. Meanwhile, such membranes exhibit excellent self-repairing properties so that physical scratching damage, such as cutting a trench, does not affect the liquid-repelling performance. The liquid-repelling ability could be recovered completely within 10 s. More significantly, such a SLIPS membrane shows excellent durability so that the water sliding angle of the SLIPS could be maintained at less than 5.0? for about 80 cycles owing to the regenerated poly(dimethylsiloxane) layer on the surface. This work represents a robust methodology to enrich the development of hydrophobic and oleophobic slippery surfaces, which is promising for many areas, such as biomedical, self-cleaning, antifouling, and self-repairing materials.

Preparation and recyclable catalysis performance of functional macroporous polyHIPE immobilized with gold nanoparticles on its surface

High internal phase emulsion polymerization was adopted for preparing macroporous polymeric monoliths, polyHIPE–Br (PHIPE–Br). Macroporous PHIPE–Br was used as the initiator to initiate the atom transfer radical polymerization (ATRP) of glycidyl methacrylate (GMA), resulting in a dense coating of polymers on the PHIPE surface and PHIPE–PGMA was obtained. Through a ring-opening addition reaction with TETA, a surface amino-polymer modified functional macroporous PHIPE–PGMA–TETA, was prepared conveniently. Gold nanoparticles could be easily in situ prepared and immobilized on the surface of PHIPE–PGMA–TETA. Characterization by scanning electron microscopy (SEM), EDX-mapping and TGA showed that PHIPE–PGMA–TETA was immobilized by the gold nanoparticles, and presented good catalytic properties. Moreover, the macroporous catalytic material, PHIPE–PGMA–TETA/Au NPs, presented recyclable catalytic performance without any decrease in activity. The materials and methods to form the monoliths and immobilize metal nanoparticles were simple and efficient, thus, opening new possibilities for highly porous PHIPE in catalysis applications.

The macroporous material PHIPE–PGMA–TETA/Au NPs has an open-cell and porous structure, and can effectively catalyze the reduction of 4-nitrophenol.

Surface glycopolymer-modified functional macroporous polyHIPE obtained by ATRP for the removal of boron in water

Macroporous polymeric monoliths PHIPE-PGAMA were obtained from polyHIPE with surface modification of PGAMA and used for boron removal.

Preparation of a Sulfur-Functionalized Microporous Polymer Sponge and In Situ Growth of Silver Nanoparticles: A Compressible Monolithic Catalyst

We report a compressible monolithic catalyst based on a microporous organic polymer (MOP) sponge. The monolithic MOP sponge was synthesized via Sonogashira-Hagihara coupling reaction between 1,4-diiodotetrafluorobenzene and 1,3,5-triethynylbenzene in a cosolvent of toluene and TEA (2:1, v/v) without stirring. The MOP sponge had an intriguing microstructure, where tubular polymer fibers having a diameter of hundreds of nanometers were entangled. It showed hierarchical porosity with a Brunauer-Emmett-Teller (BET) surface area of 512 m² g^-1. The MOP sponge was functionalized with sulfur groups by the thiol-yne reaction. The functionalized MOP sponge exhibited a higher BET surface area than the MOP sponge by 13% due to the increase in the total pore and micropore volumes. A MOP sponge-Ag heterogeneous catalyst (S-MOPS-Ag) was prepared by in situ growth of silver nanoparticles inside the sulfur-functionalized MOP sponge by the reduction of Ag⁺ ions. The catalytic activity of S-MOPS-Ag was investigated for the reduction reaction of 4-nitrophenol in an aqueous condition. When S-MOPS-Ag was compressed and released during the reaction, the rate of the reaction was considerably increased. S-MOPS-Ag was easily removed from the reaction mixture owing to its monolithic character and was reused after washing and drying.

PEO-based brush-type amphiphilic macro-RAFT agents and their assembled polyHIPE monolithic structures for applications in separation science

Polymerized High Internal Phase Emulsions (PolyHIPEs) were prepared using emulsion-templating, stabilized by an amphiphilic diblock copolymer prepared by reversible addition fragmentation chain transfer (RAFT) polymerization. The diblock copolymer consisted of a hydrophilic poly(ethylene glycol) methyl ether acrylate (PEO MA, average Mn 480) segment and a hydrophobic styrene segment, with a trithiocarbonate end-group. These diblock copolymers were the sole emulsifiers used in stabilizing "inverse" (oil-in-water) high internal phase emulsion templates, which upon polymerization resulted in a polyHIPE exhibiting a highly interconnected monolithic structure. The polyHIPEs were characterized by FTIR spectroscopy, BET surface area measurements, SEM, SEM-EDX, and TGA. These materials were subsequently investigated as stationary phase for high-performance liquid chromatography (HPLC) via in situ polymerization in a capillary format as a 'column housing'. Initial separation assessments in reversed-phase (RP) and hydrophilic interaction liquid chromatographic (HILIC) modes have shown that these polyHIPEs are decorated with different microenvironments amongst the voids or domains of the monolithic structure. Chromatographic results suggested the existence of RP/HILIC mixed mode with promising performance for the separation of small molecules.

Macroporous Polymers with Aligned Microporous Walls from Pickering High Internal Phase Emulsions

A novel class of macroporous polymers, open macroporous polymers with aligned microporous void walls, were prepared by combining particle-stabilized high internal phase emulsion (Pickering HIPE) and unidirectional freezing technique. These Pickering HIPEs were prepared by utilizing poly(urethane urea)/(vinyl ester resin) nanoparticles as the sole stabilizer, and this nanoparticles also acted as building blocks for the resulting macroporous polymers. Moreover, the morphology and compression modulus of the resulting porous materials could be tuned easily. This means now Pickering-HIPE templated open-cell foams can be prepared, and this route was normally achieved with surfactant and/or chemical reaction involved.

Novel in-capillary polymeric monoliths arising from glycerol carbonate methacrylate for flow-through catalytic and chromatographic applications

In-capillary reactive polymer monoliths have been prepared from glycerol carbonate methacrylate functional monomer, suitably functionalized and further applied to separation science and flow-through catalysis, respectively.

Polyamino amphiphile mediated support of platinum nanoparticles on polyHIPE as an over 1500-time recyclable catalyst

For supported metal nanoparticles, the ligand/support is crucial to their catalytic activity, stability and recyclability.