Ionic‐Liquid‐Grafted Rigid Poly(p‐Phenylene) Microspheres: Efficient Heterogeneous Media for Metal Scavenging and Catalysis

Novel guanidinium ionic liquid‐grafted rigid poly(p‐phenylene) (PPPIL) microspheres have been developed for metal scavenging and catalysis. The noble‐metal nanoparticles supported on the microspheres surface can be used as efficient heterogeneous catalysts. The combination of nanoparticles and ionic liquid fragments on the microsphere surfaces enhance the activity and durability of the catalyst. The PPPIL ? Pd⁰ catalyst has been tested in the Suzuki cross‐coupling reaction, and exhibits much higher catalytic activity than Pd catalysts supported on porous polymer matrices. The PPPIL ? Pd⁰ catalyst can be recycled at least for nine runs without any significant loss of activity. The present approach may, therefore, have potential applications in transition‐metal‐nanocatalyzed reactions.     

Characterisation of Solute Mobility in Hypercross‐Linked Resins in Solvents of Different Polarity: Two Promising Supports for Catalysis

Two hypercross‐linked resins stemming from a gel‐type poly‐chloromethylated styrene‐divinylbenzene resin (GT) in beaded form are investigated with a combination of spectroscopic techniques (EPR and time‐domain (TD)‐NMR spectroscopy) to evaluate their use as supports for the development of operationally flexible heterogeneous metal catalysts, suitable to be employed in liquid and gas phase. The first resin (HGT) is the direct product of the hypercross‐linking reaction, whereas the second one (HGS) is the sulphonated analogue of HGT obtained by exchanging approximately 3 wt % of the chloromethyl groups with sulphonic groups. HGT and HGS absorb both polar and apolar solvents in the permanent nanoporosity created by the hypercross‐linking, and NMR data highlight that the pore size is not affected by the different properties of the investigated liquid media. The EPR analysis of the dry resins reveals that during the hypercross‐linking process paramagnetic species are formed in the HGT beads, which persist in the sulphonated resin. The mobility of solutes inside the polymers framework was investigated with EPR spectroscopy upon soaking the resins with solutions of two spin probes (2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) and 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPOL)) in THF, toluene, n‐heptane and water. The EPR spectra show that, depending on the solvent, the two resins can act as sorbents, able to trap the solutes in the polymer framework, or as simple supports that allow free diffusion of the solutes. Our results suggest that HGT and HGS are promising supporting materials for metal catalysts, provided one chooses carefully the solvent to be employed for the catalysed reaction as this choice strongly affects the mobility of the substrates and, thus their effective reactivity.     

Bottom‐Up Construction of Mesoporous Nanotubes from 78‐Component Self‐Assembled Nanobarrels

Segmental and continuous hexagonal‐packed mesoporous metal–organic nanotubes (MMONTs) with outside diameters of up to 4.5 nm and channel sizes of 2.4 nm were hierarchically constructed by a rational multicomponent self‐assembly process involving starting from [L₂Pd₂(NO₃)₂] (L=o‐phenanthroline or 2,2′‐bipyridine) and 4‐pyridinyl‐3‐pyrazole. An unprecedented crystallization‐driven cross‐linking between discrete nanobarrel building units by spontaneous loss of the capping ligands to form infinite nanotubes was observed. Such a barrel‐to‐tube transformation provides new possibilities for the fabrication of MMONTs using the solution bottom‐up approach.     

Photo‐induced cross‐linking mechanism in azide–novolac negative photoresists: molecular level investigation using NMR spectroscopy

Negative photoresists are composed of a photoactive component (aromatic azides/bisazides) and cyclized rubber or novolac resin dissolved in an organic solvent. Hydrogen abstraction and/or insertion reaction of the reactive nitrene intermediate formed during photoirradiation of the azide result in a cross‐linked network of the novolac resin. The molecular weight of novolac resin in the exposed part of the photoresist film thus increases compared with that of the unexposed part. This makes the exposed part insoluble in the alkaline developer. Exploiting this change in physical property, a pattern can be transferred to a substrate from a mask. A better understanding of the exact mechanism of cross‐linking reactions is very important to the design of a high‐performing negative photoresist. A quinone–imine‐type complex has been proposed earlier involving the aromatic moiety of novolac resin as the reaction site. A more recent study focuses the attack of nitrene on the methylenic bridge and hydroxyl group of novolac resins, which were found to be responsible for the cross‐linking reaction along with the aromatic moiety of novolac resin. However, in our study no evidence was found for the involvement of a methylenic hydrogen or aromatic moiety of novolac resin in the cross‐linking reaction. The ¹H NMR, ¹³C NMR and DEPT‐135 spectra before and after photolysis indicate that the cross‐linking site is predominantly the hydroxyl group of novolac resin. Multiple reaction sites of attack for the nitrene intermediate have been demonstrated in cashew nut shell liquid (CNSL)‐based novolac resin by ¹H NMR spectroscopy, which in turn further increases the cross‐linked network in the exposed part of a negative photoresist. Copyright © 2003 John Wiley & Sons, Ltd.     

Poly(styrene‐co‐glycerol dimethacrylate): Synthesis,characterization, and application as a resin for gel‐phase peptide synthesis

An efficient cross‐linked polymer support for solid‐phase synthesis was prepared by introducing glycerol dimethacrylate cross‐linker to polystyrene network using free radical aqueous suspension polymerization. The support was characterized by various spectroscopic methods. Morphological feature of the resin was analyzed by microscopy. The polymerization reaction was investigated with respect to the effect of amount of cross‐linking agent, which in turn vary the swelling, loading, and the mechanical stability of the resin. The solvent uptake of the polymer was studied in relation to cross‐linking and compared with Merrifield resin. The stability of the resin was tested in different synthetic conditions used for solid‐phase peptide synthesis. Hydroxy group of the support was derivatized to chloro and then amino groups using different reagents and reaction conditions. Efficiency of the support was tested and compared with TentaGel? resin by following different steps involved in the synthesis of the 65–74 fragment of acyl carrier protein. The results showed that the poly(styrene‐co‐glycerol dimethacrylate) (GDMA‐PS) is equally efficient as TentaGel resin in peptide synthesis. The purity of the peptides was analyzed by HPLC and identities were determined by mass spectroscopy and amino acid analysis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4382–4392, 2005     

Synthesis and characterization of polymer electrolytes based on cross‐linked phenoxy‐containing polyphosphazenes

A new method to prepare the polymer electrolytes for lithium‐ion batteries is proposed. The polymer electrolytes were prepared by reacting poly(phosphazene)s (MEEPP) having 2‐(2‐methoxyethoxy)ethoxy and 2‐(phenoxy)ethoxy units with 2,4,6‐tris[bis(methoxymethyl)amino]‐1,3,5‐triazine (CYMEL) as a cross‐linking agent. This method is simple and reliable for controlling the cross‐linking extent, thereby providing a straightforward way to produce a flexible polymer electrolyte membrane. The 6 mol % cross‐linked polymer electrolyte (ethylene oxide unit (EO)/Li = 24:1) exhibited a maximum ionic conductivity of 5.36 × 10^?5 S cm^?1 at 100 °C. The ⁷Li linewidths of solid‐state static NMR showed that the ionic conductivity was strongly related to polymer segment motion. Moreover, the electrochemical stability of the MEEPP polymer electrolytes increased with an increasing extent of cross‐linking, the highest oxidation voltage of which reached as high as 7.0 V. Moreover, phenoxy‐containing polyphosphazenes are very useful model polymers to study the relationship between the polymer flexibility; that is, the cross‐linking extent and the mobility of metal ions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 352–358     

Examination of selected synthesis parameters for typical wood adhesive‐type urea–formaldehyde resins by 13C NMR spectroscopy. I

Selected synthesis parameters of typical wood adhesive‐type urea–formaldehyde (UF) resins were examined using the ¹³C NMR spectroscopy. The monomeric hydroxymethylureas and methylene–ether derivatives formed in the initial alkaline reaction polymerize in the subsequent acidic reaction by forming methylene bonds and cleaving some hydroxymethyl groups as formaldehyde. For typical resin syntheses at F/U ratio of 2.10, the resulting UF polymer is found to be a number‐averaged pentamer having 3.25 polymer chain branches with about 80% of chain ends bonded to hydroxymethyl groups and the rest being free amide groups. When the second urea is added during the cooling period, about 67% of hydroxymethyl groups cleave from the UF polymeric components and the freed formaldehyde reacts with second urea to form monomeric hydroxymethylureas. This hydroxymethyl group move is suppressed when the second urea is added at low temperatures, suggesting that wood adhesive‐type UF resins are composed of monomeric and polymeric UF components having hydroxymethyl functional groups in varying proportions. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 995–1007, 1999     

Heterophase Photocatalysts from Water‐Soluble Conjugated Polyelectrolytes: An Example of Self‐Initiation under Visible Light

We herein report a new design route to stable, heterophase photocatalysts, which function as highly dispersible conjugated polymer nanoparticles and porous monoliths under visible light in aqueous medium. They were constructed by attachment of the ionic‐liquid species 1‐alkyl‐3‐vinylimidazolium bromide onto the side chains of a photoactive polymer. The structure configuration allows not only photocatalysis in aqueous environment but also a unique self‐initiation radical cross‐linking process to transform the water‐soluble photoactive polymer into a heterophase system, either as nanoparticles or a porous monolith. High photocatalytic activity and reusability of the heterophase system were demonstrated in the degradation of organic dyes and reduction of Cr^VI into Cr^III in water under visible‐light irradiation.     

Time‐Controllable Lipophilic‐Drug Release System Designed by Loading Lipid Nanoparticles into Polysaccharide Hydrogels

A hybrid hydrogel composed of solid lipid nanoparticles (LNPs) entrapped within chemically cross‐linked carboxymethylcellulose (CMC) is developed to achieve localized and sustained release of lipophilic drugs. The analysis of LNP stability as well as the hydrogel swelling and mechanical properties confirm the successful incorporation of particles up to a concentration of 50% w/w_CMC. The initial LNP release rate can be prolonged by increasing the particle diameter from 50 to 120 nm, while the amount of long‐term release can be adjusted by tailoring the particle surface charge or the cross‐linking density of the polymer. After 30 d, 58% of 50 nm diameter negatively charged LNPs escape from the matrix while only 17% of positively charged nanoparticles are released from materials with intermediate cross‐linking density. A mathematical diffusion model based on Fick's second law is efficient to predict the diffusion of the particles from the hydrogels.     

Threonine stabilizer‐controlled well‐dispersed small palladium nanoparticles on modified magnetic nanocatalyst for Heck cross‐coupling process in water

We report the synthesis of magnetically separable Fe₃O₄@Silica‐Threonine‐Pd⁰ magnetic nanoparticles with a core–shell structure. After synthesis of Fe₃O₄@Silica, threonine as an efficient stabilizer/ligand was bonded to the surface of Fe₃O₄@Silica. Then, palladium nanoparticles were generated on the threonine‐modified catalyst. The threonine stabilizer helps to generate palladium nanoparticles of small size (less than 4 nm) with high dispersity and uniformity. Magnetically separable Fe₃O₄@Silica‐Threonine‐Pd⁰ nanocatalyst was fully characterized using various techniques. This nanocatalyst efficiently catalysed the Heck cross‐coupling reaction of a variety of substrates in water medium as a green, safe and inexpensive solvent at 80°C. The Fe₃O₄@Silica‐Threonine‐Pd⁰ catalyst was used for at least eight successful consecutive runs with palladium leaching of only 0.05%.     

Energy/Hole Transfer Phenomena in Hybrid α‐Sexithiophene (α‐STH) Nanoparticle–CdTe Quantum‐Dot Nanocomposites

Considerable attention has been paid to hybrid organic–inorganic nanocomposites for designing new optical materials. Herein, we demonstrate the energy and hole transfer of hybrid hole‐transporting α‐sexithiophene (α‐STH) nanoparticle–CdTe quantum dot (QD) nanocomposites using steady‐state and time‐resolved spectroscopy. Absorption and photoluminescence studies confirm the loss of planarity of the α‐sexithiophene molecule due to the formation of polymer nanoparticles. Upon photoexcitation at 370 nm, a nonradiative energy transfer (73 %) occurs from the hole‐transporting α‐STH nanoparticles to the CdTe nanoparticles with a rate of energy transfer of 6.13×10⁹ s^?1. However, photoluminescence quenching of the CdTe QDs in the presence of the hole‐transporting α‐STH nanoparticles is observed at 490 nm excitation, which is due to both static‐quenching and hole‐transfer‐based dynamic‐quenching phenomena. The calculated hole‐transporting rate is 7.13×10⁷ s^?1 in the presence of 42×10^?8 M α‐STH nanoparticles. Our findings suggest that the interest in α‐sexithiophene (α‐STH) nanoparticle–CdTe QD hybrid nanocomposites might grow in the coming years because of various potential applications, such as solar cells, optoelectronic devices, and so on.     

Determination of methylene bridge crosslinking in chloromethylated PS‐DVB resins

We present the development of a method for the determination of methylene bridge crosslinking in ¹³C‐labeled chloromethylated polystyrene‐divinylbenzene resins. Our system uses a new room temperature reduction of the chloromethyl groups that circumvents the possible challenges associated with additional crosslinking. We demonstrate how the reduction of the chloromethyl groups allowed for the determination of methylene bridging, derived from the methylenebis(ethenylbenzene) crosslinker, based on the integration of the methylene signal in the ¹³C NMR spectra. Utilizing this method, the total crosslinking within the chloromethylated resin generated at 35 °C was determined to be upward of 10 wt %, which increased from 6 wt % in the unfunctionalized resin. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1955–1960     

Trifluoromethylthiolation of Aryl Iodides and Bromides Enabled by a Bench‐Stable and Easy‐To‐Recover Dinuclear Palladium(I) Catalyst

While palladium catalysis is ubiquitous in modern chemical research, the recovery of the active transition‐metal complex under routine laboratory applications is frequently challenging. Described herein is the concept of alternative cross‐coupling cycles with a more robust (air‐, moisture‐, and thermally‐stable) dinuclear Pd^I complex, thus avoiding the handling of sensitive Pd⁰ species or ligands. Highly efficient C? SCF₃ coupling of a range of aryl iodides and bromides was achieved, and the recovery of the Pd^I complex was accomplished via simple open‐atmosphere column chromatography. Kinetic and computational data support the feasibility of dinuclear Pd^I catalysis. A novel SCF₃‐bridged Pd^I dimer was isolated, characterized by X‐ray crystallography, and verified to be a competent catalytic intermediate.     

Directed C−H Activation and Tandem Cross‐Coupling Reactions Using Palladium Nanocatalysts with Controlled Oxidation

Controlled oxidation of palladium nanoparticles provided high‐valent Pd^IV oxo‐clusters which efficiently promote directed C−H halogenation reactions. In addition, palladium nanoparticles can undergo changes in oxidation states to provide both high‐valent Pd^IV and low‐valent Pd⁰ species within one system, and thus a tandem reaction of C−H halogenation and cross‐coupling (C−N, C−C, and C−S bond formation) was successfully established.     

Preparation and Characterization of Transparent and UV‐Shielding Epoxy/SR‐494/APTMS/ZnO Nanocomposites with High Heat Resistance and Anti‐Static Properties

This research is to develop transparent and UV‐shielding Epoxy/SR‐494/APTMS/ZnO nanocomposite materials with high heat resistant and anti‐static properties. Firstly, the APTMS (3‐(acryloxypropyl)trimethoxysilane) performs the silanol intermediates by hydrolysis in pH 4～5 acid solution. The inorganic anti‐static fillers of powder ZnO can be successfully coupled and crosslinked to Epoxy/SR‐494 organic matrixes with these silanols of APTMS coupling agents. The remained active ‐OH functional groups of the APTMS/ZnO complexes can network bonding with epoxy prepolymers. Therefore, the Epoxy/APTMS/ZnO complexes with good anti‐static composites will be successfully prepared. Finally, in order to improve the thermal resistant and mechanical properties, the polyfunctionalized SR‐494 (pentaery‐thritol tetracrylate) acrylate monomers and the Epoxy/APTMS/ZnO composites are chain polymerized to form an excellent cross‐linking structure of organic/inorganic nanocomposites. The chemical bonding formation and the best weight contents of reaction components are identified by FT‐IR spectra. The thermal resistance, transparence, surface electric resistance, and hardness of these nanocomposites are measured by TGA, DSC, UV‐Visible, surface resistant meter, and pencil hardness tester respectively. Experimental results show that these nanocomposites have 90% transmittance and the best Td value is 389.3 °C which is 109.0 °C and 78.6 °C higher than those of pure epoxy resin and pure SR‐494 acrylate resin respectively. The glass transition temperature is not detected below 200 °C. The surface electric resistances of Epoxy/SR‐494/APTMS/ZnO hybrid thin films are decreased from 3.14 × 10¹³ to 5.13 × 10⁷ Ω/cm². The hardness of these nanocomposites is as high as 8H, and those hybrid films have high UV‐shielding properties. The morphology structures of the hybrid thin films are estimated by SEM. The results show that the optical thin films are evenly distributed with inorganic colloidal particles and the average particle size of these nanocomposites is 45～80 nm, while the powder ZnO (particle size: 2～5 μm) was used as inorganic filler.     

Highly Hydrophilic Copolymers of N,N‐Dimethylacrylamide,Acrylamido‐2‐methylpropanesulfonic acid,and Ethylenedimethacrylate: Nanoscale Morphology in the Swollen State and Use as Exotemplates for Synthesis of Nanostructured Ferric Oxide

The polymer framework of water‐swollen copolymers of N,N‐dimethylacrylamide, acrylamido‐2‐methylpropanesulfonic acid, and ethylenedimethacrylate (nominal cross‐linking degrees of 4, 8, and 20 mol %) is composed of highly expanded domains, with “pores” not less than 6 nm in diameter. When the 4 % cross‐linked copolymer (DAE 26‐4) is swollen with a 10^?4 M solution of 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPOL) in water, MeOH, EtOH, or nBuOH, the molecules of the paramagnetic probe rotate rapidly (τ<1000 ps) and as fast as in the bulk liquid in the case of water. The swelling degree of DAE 26‐4 is related to the Hansen solubility parameters of a number of liquids, including linear alcohols up to n‐octanol. It is also found that the rotational correlation time of TEMPOL in the copolymer swollen by water and the lightest alcohols increases with decreasing specific absorbed volume. Time‐domain NMR spectrometry of water‐swollen DAE 26‐4 shows that sorption of only 14 % of the liquid required for its complete swelling is enough for full hydration of the polymer chains. Accordingly, in fully swollen DAE 26‐4 the longitudinal relaxation time of water closely approaches the value of pure water. {¹³C} CP‐MAS NMR on partially and fully water swollen samples of DAE 26‐4 shows that swelling increases the mobility of the polymer chains, as clearly indicated by the narrowing of the best‐resolved peaks. DAE 26‐4 was used as an exotemplate for the synthesis of nanocomposites composed of the polymer and nanostructured Fe₂O₃ through a series of ion‐exchange/precipitation cycles. After the first cycle the nanoparticles are 3–4 nm in diameter, with practically unchanged size after subsequent cycles (up to five). In fact, the nanoparticle size never exceeded the diameter of the largest available pores. This suggests that the polymer framework controls the growth of the nanoparticles according to the template‐controlled synthesis scheme. Selected‐area electron diffraction, TEM, and high‐resolution electron microscopy show that the nanostructured inorganic phase is composed of hematite.     

Carboxymethylcellulose‐supported palladium nanoparticles generated in situ from palladium(II) carboxymethylcellulose as an efficient and reusable catalyst for ligand‐ and base‐free Heck–Matsuda and Suzuki–Miyaura couplings

A novel palladium(II) carboxymethylcellulose (CMC‐Pd^II) was prepared by direct metathesis from sodium carboxymethylcellulose and PdCl₂ in aqueous solution. Its catalytic activities were explored for Heck–Matsuda reactions of aryldiazonium tetrafluoroborate with olefins, and Suzuki–Miyaura couplings of aryldiazonium tetrafluoroborate with arylboronic acid. Both reactions proceeded at room temperature in water or aqueous ethanol media without the presence of any ligand or base, to provide the corresponding cross‐coupling products in good to excellent yields under atmospheric conditions. The CMC‐Pd^II and carboxymethylcellulose‐supported palladium nanoparticles (CMC‐Pd⁰) formed in situ in the reactions were characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, inductively coupled plasma atomic emission spectrometry, and scanning and transmission electron microscopies. The homogeneous nature of the CMC‐Pd⁰ catalyst was confirmed via Hg(0) and CS₂ poisoning tests. Moreover, the CMC‐Pd⁰ catalyst could be conveniently recovered by simple filtration and reused for at least ten cycles in Suzuki–Miyaura reactions without apparently losing its catalytic activity. The catalytic system not only overcomes the basic drawbacks of homogeneous catalyst recovery and reuse but also avoids the need to fabricate palladium nanoparticles in advance. Copyright © 2015 John Wiley & Sons, Ltd.     

New anti‐bacterial polychelates: synthesis,characterization, and anti‐bacterial activities of thiosemicarbazide–formaldehyde resin and its polymer–metal complexes

New polymeric ligand (resin) was prepared by the condensation of thiosemicarbazides with formaldehyde in the presence of acidic medium. Thisemicarbazide–formaldehyde polymer–metal complexes were prepared with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) in 1:2 metal:ligand molar ratio. The polymeric ligand and its polymer–metal complexes were characterized by elemental analysis, thermogravimetric analysis (TGA), FTIR, ¹³C NMR and ¹H NMR. The geometry of central metal ions was conformed by electronic (UV–vis) and EPR spectra. The antibacterial activities of all the synthesized polymers were investigated against Bacillus subtilis and Staphylococcus aureus (Gram‐positive) and Escherichia coli and Salmonella typhi (Gram‐negative). These compounds showed excellent activities against these bacteria using the shaking flask method. Copyright © 2008 John Wiley & Sons, Ltd.     

Photoswitchable Formation of a DNA Interstrand Cross‐Link by a Coumarin‐Modified Nucleotide

A coumarin‐modified pyrimidine nucleoside ( 1 ) has been synthesized using a Cu^I‐catalyzed click reaction and incorporated into oligodeoxynucleotides (ODNs). Interstrand cross‐links are produced upon irradiation of ODNs containing 1 at 350 nm. Cross‐linking occurs through a [2+2] cycloaddition reaction with the opposing thymidine, 2′‐deoxycytidine, or 2′‐deoxyadenosine. A much higher reactivity was observed with dT than dC or dA. Irradiation of the dT‐ 1 and dC‐ 1 cross‐linked products at 254 nm leads to a reversible ring‐opening reaction, while such phenomena were not observed with dA‐ 1 adducts. The reversible reaction is ultrafast and complete within 50–90 s. Consistent photoswitching behavior was observed over 6 cycles of irradiation at 350 nm and 254 nm. To the best of our knowledge, this is the first example of photoswitchable interstrand cross‐linking formation induced by a modified pyrimidine nucleoside.     

Bismetal Complexes of 5,20‐Bis(5‐formyl‐2‐pyrrolyl)‐[26]hexaphyrin(1.1.1.1.1.1) Exhibiting Strong Near‐Infrared Region Absorptions

[26]Hexaphyrin(1.1.1.1.1.1) bearing two 5‐formyl‐2‐pyrrolyl groups at the 5‐ and 20‐positions was prepared by cross‐condensation of 5,10‐bis(pentafluorophenyl)‐substituted tripyrrane with 2,5‐diformylpyrrole as an effective binuclear metal‐coordinating ligand, owing to the two hemiporphyrin‐like NNNN pockets. In fact, metalation of this hexaphyrin with Zn^II, Cu^II, and Pd^II salts proceed smoothly at room temperature to give the corresponding bismetal complexes that displayed remarkably redshifted absorption spectra reaching deep into near infrared region. These redshifted absorption bands are ascribed, through electrochemical investigations and DFT calculations, to two structural motifs: the N‐metalopyrrole substructure that elevates the HOMO level due to the electron‐donating property and the two coordinated metal ions that serve as Lewis acids to lower the LUMO level.