Hyper-Cross-Linked Polyphosphines as Nanoporous Macroligands-A Systematic Study on Cross-Linking and Their Catalytic Application in the CO2 Hydrogenation

Hyper-cross-linked polymers (HCPs) enable the tailored synthesis of functionalized materials and provide a versatile design strategy for porous macroligands. Based on the prototypical triphenylphosphine (PPh3) monomer, we investigate the role of the involved cross-linking reagents in the formation of polyphosphines and evaluate structure-activity relations for application in the catalytic CO2 hydrogenation: namely by varying the Friedel-Crafts catalyst, the cross-linker unit and the degree of cross-linking. The study of monomeric reactivities shows that phosphines are insufficiently activated by iron chloride catalyzed cross-linking and that the stronger aluminum chloride is required to ensure PPh3 incorporation. Applying aromatic cross-linker units introduces porosity and promotes the accessibility of ligating centers for the immobilized ruthenium species. The thus formed solid catalysts exhibit excellent performances in the hydrogenation of CO2 to formic acid in the aqueous phase and are studied in successive recycling runs. The partial structural degradation of the frameworks during catalysis is addressed by adjusting higher degrees of cross-linking, leading to an improved stabilization of the catalyst. Overall, this study highlights cross-linking strategies for the tailoring of phosphine-based HCPs and the design of stable macroligands under catalytic conditions.

Preparation of nitrogen doped hyper-crosslinked polymer-based hard carbon for high performance Li+/Na+ battery anode

Hyper cross-linked polymers (HCPs), as a key precursor of hard carbon (HC) anode materials, stand out because of their capacity for molecular-scale structural design and comparatively straightforward preparation techniques, which are not seen in other porous materials synthesized procedure. A novel synthesis method of HCPs is developed in this paper, which is through the incorporation of functional macromolecules, the structural control and heteroatom doping of the product has been achieved, thus augmenting its electrochemical performance in batteries. In this work, carbonized tetraphenylporphyrin zinc (TPP-Zn) doped HCP-based hard carbon (CTHCP) with stable structure was prepared by Friedel-Crafts reaction and carbonization by using naphthalene and trace TPP-Zn as monomers, dimethoxybenzene (DMB) as crosslinking agent and FeCl3 as catalyst. The introduction of TPP-Zn, a functional macromolecule with unique two-dimensional structure, realized the pore structure regulation and N doping of the raw carbonized HCP-based hard carbon (CHCP). The results showed that CTHCP had higher mesoporous volume, N content and wider layer spacing than CHCP. In addition, CTHCP anode exhibited excellent Li+/Na+ storage performance, initial reversible capacity, rate performance and long cycle life. More amount of N-containing (N-5) active sites and mesoporous content in CTHCP anode was the main reason for the improvement of Na+ storage effect. While the increased interlayer spacing had a greater effect on the lithium storage capacity. This study uncovered the design rules of HC anode materials suitable for Li+/Na+ batteries and provided a new idea for the preparation of high-performance HC anode materials.

Conjugated Microporous Polymers for Catalytic CO2 Conversion

Rising carbon dioxide (CO2) levels in the atmosphere are recognized as a threat to atmospheric stability and life. Although this greenhouse gas is being produced on a large scale, there are solutions to reduction and indeed utilization of the gas. Many of these solutions involve costly or unstable technologies, such as air-sensitive metal-organic frameworks (MOFs) for CO2 capture or "non-green" systems such as amine scrubbing. Conjugated microporous polymers (CMPs) represent a simpler, cheaper, and greener solution to CO2 capture and utilization. They are often easy to synthesize at scale (a one pot reaction in many cases), chemically and thermally stable (especially in comparison with their MOF and covalent organic framework (COF) counterparts, owing to their amorphous nature), and, as a result, cheap to manufacture. Furthermore, their large surface areas, tunable porous frameworks and chemical structures mean they are reported as highly efficient CO2 capture motifs. In addition, they provide a dual pathway to utilize captured CO2 via chemical conversion or electrochemical reduction into industrially valuable products. Recent studies show that all these attractive properties can be realized in metal-free CMPs, presenting a truly green option. The promising results in these two fields of CMP applications are reviewed and explored here.

Nickel-palladium bimetallic nanoparticles supported on multi-walled carbon nanotubes; versatile catalyst for Sonogashira cross-coupling reactions

We have developed an efficient method to generate highly active nickel-palladium bimetallic nanoparticles supported on multi-walled carbon nanotubes (Ni-Pd/MWCNTs) by dry mixing of the nickel and palladium salts utilizing the mechanical energy of a ball-mill. These nanoparticles were successfully employed in Sonogashira cross-coupling reactions with a wide array of functionalized aryl halides and terminal alkynes under ligand and copper free conditions using a Monowave 50 heating reactor. Notably, the concentration of palladium can be lowered to a minimum amount of 0.81% and replaced by more abundant and less expensive nickel nanoparticles while effectively catalyzing the reaction. The remarkable reactivity of the Ni-Pd/MWCNTs catalyst toward Sonogashira cross-coupling reactions is attributed to the high degree of the dispersion of Ni-Pd nanoparticles with small particle size of 5-10 nm due to an efficient grinding method. The catalyst was easily removed from the reaction mixture by centrifugation and reused several times with minimal loss of catalytic activity. Furthermore, the concentration of catalyst in Sonogashira reactions can be reduced to a minimum amount of 0.01 mol% while still providing a high conversion of the Sonogashira product with a remarkable turnover number (TON) of 7200 and turnover frequency (TOF) of 21 600 h^-1. The catalyst was fully characterized by a variety of spectroscopic techniques including X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).

BODIPY-Based Polymers of Intrinsic Microporosity for the Photocatalytic Detoxification of a Chemical Threat

Effective heterogeneous photocatalysts capable of detoxifying chemical threats in practical settings must exhibit outstanding device integrity. We report a copolymerization that yields robust, porous, processible, chromophoric BODIPY (BDP; boron-dipyrromethene)-containing polymers of intrinsic microporosity (BDP-PIMs). Installation of a pentafluorophenyl at the meso position of a BDP produced reactive monomer that when combined with 5,5,6,6-tetrahydroxy-3,3,3,3-tetramethyl-1,1-spirobisindane (TTSBI) and tetrafluoroterephthalonitrile (TFTPN) yields PIM-1. Postsynthetic modification of these polymers yields Br-BDP-PIM-1a and -1b─polymers containing bromine at the 2,6-positions. Remarkably, the brominated polymers display porosity and processability features similar to those of H-BDP-PIMs. Gas adsorption reveals molecular-scale porosity and Brunette-Emmet-Teller surface areas as high as 680 m² g^-1. Electronic absorption spectra reveal charge-transfer (CT) bands centered at 660 nm, while bands arising from local excitations, LE, of BDP and TFTPN units are at 530 and 430 nm, respectively. Fluorescence spectra of the polymers reveal a Förster resonance energy-transfer (FRET) pathway to BDP units when TFTPN units are excited at 430 nm; weak phosphorescence at room temperature indicates a singlet-to-triplet intersystem crossing. The low-lying triplet state is well positioned energetically to sensitize the conversion of ground-state (triplet) molecular oxygen to electronically excited singlet oxygen. Photosensitization capabilities of these polymers toward singlet-oxygen-driven detoxification of a sulfur-mustard simulant 2-chloroethyl ethyl sulfide (CEES) have been examined. While excitation of CT and LE_BDP bands yields weak catalytic activity (t_1/2 > 15 min), excitation to higher energy states of TFTPN induces significant increases in photoactivity (t_1/2 ≅ 5 min). The increase is attributable to (i) enhanced light collection, (ii) FRET between TFTPN and BDP, (iii) the presence of heavy atoms (bromine) having large spin-orbit coupling energies that can facilitate intersystem crossing from donor-acceptor CT-, FRET-, or LE-generated BDP singlet states to BDP-related triplet states, and (iv) polymer triplet excited-state sensitization of the formation of CEES-reactive, singlet oxygen.

New Approach in the Application of Conjugated Polymers: The Light-Activated Source of Versatile Singlet Oxygen Molecule

For many years, the research on conjugated polymers (CPs) has been mainly focused on their application in organic electronics. Recent works, however, show that due to the unique optical and photophysical properties of CPs, such as high absorption in UV–Vis or even near-infrared (NIR) region and efficient intra-/intermolecular energy transfer, which can be relatively easily optimized, CPs can be considered as an effective light-activated source of versatile and highly reactive singlet oxygen for medical or catalytic use. The aim of this short review is to present the novel possibilities that lie dormant in those exceptional polymers with the extended system of π-conjugated bonds.

A Porous Polymer-Based Solid Acid Catalyst with Excellent Amphiphilicity: An Active and Environmentally Friendly Catalyst for the Hydration of Alkynes

Developing efficient solid acid catalysts for aqueous organic reactions is of great importance for the development of sustainable chemistry. In this work, a porous polymeric acid catalyst was synthesized via a solvothermal copolymerization and a successive ion-exchange method. Physicochemical characterizations suggested that the prepared polymers possessed large Brunauer-Emmett-Teller (BET) surface areas, a hierarchically porous structure, excellent surface amphiphilicity, and nice swelling properties. Notably, an activity test in phenylacetylene hydration indicated that the prepared solid acid exhibited high catalytic activity in water, which outperformed commercial amberlyst-15, sulfuric acid, and benzenesulfonic acid. Moreover, the prepared solid acid can be easily recovered and reused at least four times. Additionally, a variety of aromatic and aliphatic alkynes could be effectively transformed into corresponding ketones under optimal reaction conditions.

Playing with covalent triazine framework tiles for improved CO2 adsorption properties and catalytic performance

The rational design and synthesis of covalent triazine frameworks (CTFs) from defined dicyano-aryl building blocks or their binary mixtures is of fundamental importance for a judicious tuning of the chemico-physical and morphological properties of this class of porous organic polymers. In fact, their gas adsorption capacity and their performance in a variety of catalytic transformations can be modulated through an appropriate selection of the building blocks. In this contribution, a set of five CTFs (CTF1-5) have been prepared under classical ionothermal conditions from single dicyano-aryl or heteroaryl systems. The as-prepared samples are highly micro-mesoporous and thermally stable materials featuring high specific surface area (up to 1860 m2·g-1) and N content (up to 29.1 wt %). All these features make them highly attractive samples for carbon capture and sequestration (CCS) applications. Indeed, selected polymers from this series rank among the CTFs with the highest CO2 uptake at ambient pressure reported so far in the literature (up to 5.23 and 3.83 mmol·g-1 at 273 and 298 K, respectively). Moreover, following our recent achievements in the field of steam- and oxygen-free dehydrogenation catalysis using CTFs as metal-free catalysts, the new samples with highest N contents have been scrutinized in the process to provide additional insights to their complex structure-activity relationship.

Progress Report on Phase Separation in Polymer Solutions

Polymeric porous media (PPM) are widely used as advanced materials, such as sound dampening foams, lithium-ion batteries, stretchable sensors, and biofilters. The functionality, reliability, and durability of these materials have a strong dependence on the microstructural patterns of PPM. One underlying mechanism for the formation of porosity in PPM is phase separation, which engenders polymer-rich and polymer-poor (pore) phases. Herein, the phase separation in polymer solutions is discussed from two different aspects: diffusion and hydrodynamic effects. For phase separation governed by diffusion, two novel morphological transitions are reviewed: "cluster-to-percolation" and "percolation-to-droplets," which are attributed to an effect that the polymer-rich and the solvent-rich phases reach the equilibrium states asynchronously. In the case dictated by hydrodynamics, a deterministic nature for the microstructural evolution during phase separation is scrutinized. The deterministic nature is caused by an interfacial-tension-gradient (solutal Marangoni force), which can lead to directional movement of droplets as well as hydrodynamic instabilities during phase separation.

On the Gas Storage Properties of 3D Porous Carbons Derived from Hyper-Crosslinked Polymers

The preparation of porous carbons by post-synthesis treatment of hypercrosslinked polymers is described, with a careful physico-chemical characterization, to obtain new materials for gas storage and separation. Different procedures, based on chemical and thermal activations, are considered; they include thermal treatment at 380 °C, and chemical activation with KOH followed by thermal treatment at 750 or 800 °C; the resulting materials are carefully characterized in their structural and textural properties. The thermal treatment at temperature below decomposition (380 °C) maintains the polymer structure, removing the side-products of the polymerization entrapped in the pores and improving the textural properties. On the other hand, the carbonization leads to a different material, enhancing both surface area and total pore volume—the textural properties of the final porous carbons are affected by the activation procedure and by the starting polymer. Different chemical activation methods and temperatures lead to different carbons with BET surface area ranging between 2318 and 2975 m²/g and pore volume up to 1.30 cc/g. The wise choice of the carbonization treatment allows the final textural properties to be finely tuned by increasing either the narrow pore fraction or the micro- and mesoporous volume. High pressure gas adsorption measurements of methane, hydrogen, and carbon dioxide of the most promising material are investigated, and the storage capacity for methane is measured and discussed.

Creating Aligned Nanopores by Magnetic Field Processing of Block Copolymer/Homopolymer Blends

We describe the phase behavior of a cylinder-forming block copolymer (BCP)/homopolymer blend and the generation of aligned nanopores by a combination of magnetic field alignment and selective removal of the minority-block-miscible homopolymer. Alignment is achieved by cooling through the order-disorder transition temperature (T_odt) in a 6 T field. The system is a blend of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) and poly(ethylene glycol) (PEG). PEG is miscible with P4VP and partitions preferentially into the cylindrical microdomains. Calorimetry and X-ray scattering show that T_odt decreases linearly with PEG concentration until the onset of macrophase separation, inferred by PEG crystallization. Beyond this point, T_odt is invariant with PEG content. Increasing PEG molar mass decreases the concentration at which macrophase separation is observed. Nanopore formation is confirmed by dye uptake experiments that show a clear dependence of dye uptake on PEG content before removal. We anticipate that this strategy can be extended to other BCP/homopolymer blends to produce nanoporous materials with reliable control of pore alignment and effective pore dimensions.

QSPR Modeling of the Refractive Index for Diverse Polymers Using 2D Descriptors

In the present work, predictive quantitative structure-property relationship models have been developed to predict refractive indices (RIs) of a set of 221 diverse organic polymers using theoretical two-dimensional descriptors generated on the basis of the structures of polymers' monomer units. Four models have been developed by applying partial least squares (PLS) regression with a different combination of six descriptors obtained via double cross-validation approaches. The predictive ability and robustness of the proposed models were checked using multiple validation strategies. Subsequently, the validated models were used for the generation of "intelligent" consensus models (http://teqip.jdvu.ac.in/QSAR_Tools/DTCLab/) to improve the quality of predictions for the external data set. The selected consensus models were used for the prediction of refractive index values of various classes of polymers. The final selected model was used to predict the refractive index of four small virtual libraries of monomers recently reported. We also used a true external data set of 98 diverse monomer units with the experimental RI values of the corresponding polymers. The obtained models showed a good predictive ability as evidenced from a very good external predicted variance.