Importance of junction functionality in highly crosslinked polymers

Summary A modification of a theoretical model for the determination of the number average molecular weight between crosslinks, ¯M_c, is presented for the case of multifunctional junction functionalities in highly crosslinked, macromolecular systems.     

Spatial distribution of functionalities in an adsorptive reactor at the particle level

The concept of adsorptive reactors has attracted considerable attention as a hybrid process to enhance reaction selectivity and conversion for heterogeneously catalysed gas phase reactions. Transport resistances affect the performance of adsorptive reactors adversely and the integration of functionalities within the same particle circumvents this limitation. Instead of a simple uniform integration of functionalities within the particle, one can also non-uniformly distribute the functionalities over the particle to exploit the concentration profiles arising from transport limitations for process enhancement. A detailed numerical investigation has been carried out to identify the optimal distribution of catalyst and adsorbent functionalities at a particle and reactor level using Aspen Custom Modeler. Though process enhancements are possible by non-uniform distribution within particle, the benefits are marginal. Nevertheless, the integration of functionalities within a particle offers significant improvements in adsorptive process performance.     

Sn(OBun)4溶胶-凝胶体系的水解缩合反应动力学

研究了乙酰丙酮(acelylacetone)改性Ⅱ三丁醇锡(tinalkoxide)在氢氟酸、盐酸、氢溴酸、硝酸、乙酸和氨催化剂作用下的溶胶-凝胶体系的动力学过程。利用近似线性聚合生长模型求出了不同催化剂作用下改性醇盐的平均缩合反应速率以及溶胶团簇的平均官能度，催化剂对平均缩合反应速率的影响按大小依次为硝酸、盐酸、乙酸、氨水和氢溴酸．各溶胶体系的平均官能度均为略大于2．0。氢氟酸作催化剂的体系产生白色沉淀。催化剂对体系凝胶时间影响大小依次为氨水、乙酸、盐酸、硝酸和氢溴酸。利用部分电荷模型计算了不同催化剂作用下改性锡醇盐分子体系的电荷分布．讨论了不同催化剂对改性锡醇盐水解和缩合反应的催化机理。     

Effect of average functionality on properties of UV-curable waterborne polyurethane-acrylate

A series of ultraviolet (UV) curable waterborne polyurethane-acrylate (WPUA) with different average functionalities were synthesized in new methods. The chemical structures of WPUA were confirmed by Fourier-transform infrared spectroscopy (FT-IR) and the effect of average functionality on properties of WPUA was systemically investigated. It was found that the average functionality had a positive effect on the water resistance and tensile strength of WPUA, to make optimal formation of WPUA molecule chains available, whereas the increasing of average functionality decreased the viscosity and extension of WPUA samples. Besides, through the investigation on the UV curing kinetics, it was found that the average functionality too high or too low was unfavorable for the increase of unsaturation conversion. The morphology and microstructure of WPUA films were also comprehensively discussed with WAXD patterns and fractured surface observed from SEM images.     

Microstructural Shape Factors: Relation of Random Planar Sections to Three-Dimensional Microstructures

The relation of random planar sections of anisometric microstructures to the actual three-dimensional anisometry is considered for oblate and prolate spheroids and cylinders. Simple formulae are obtained relating the two-dimensional (2-D) to three-dimensional (3-D) aspect ratios; for oblate systems with large aspect ratios, the area-weighted average 2-D aspect ratio varies linearly with the actual aspect ratio, whereas for prolate systems of large aspect ratio, the 2-D aspect ratio varies logarithmically with actual aspect ratio. Extension to polydisperse systems yields a shape factor, R , which gives greatest weight to grains (or particles) having the highest volume fraction. This not only preserves the linear and logarithmic functionalities found in monodisperse systems, but favorably affects the sensitivity of R to visually apparent differences among microstructures.     

Visible light-induced photodegradation of methylene blue and reduction of 4-nitrophenol to 4-aminophenol over bio-synthesized silver nanoparticles

Silver nanoparticles are synthesized by an eco-friendly protocol using Litchi chinensis fruit juice as a reducing and capping agent. UV-vis spectroscopy (SPR band around 447 nm), XRD (crystallinity), HRTEM (size and morphology), EDS (elemental composition) and FTIR (surface functionalities) were used to characterize silver nanoparticles. They are highly dispersed, mostly spherical with an average size of 10 nm. The prepared nanoparticles exhibited rapid reduction of 4-nitro phenol to 4-amino phenol (K = 0.09/min) and photodegradation of methylene blue (K = 0.0335/min) under visible light. The prepared nanoparticles could be an excellent candidate for the separation of hazardous materials.     

Ultradisperse Pt nanoparticles anchored on defect sites in oxygen-free few-layer graphene and their catalytic properties in CO oxidation

Highly uniform and crystalline ultradisperse Pt nanoparticles with average sizes of 2.4 nm were deposited on oxygen-free few-layer graphene (FLG) by polyol reduction method without any additional protective agents. The samples were analyzed by Raman spectroscopy, photoelectron spectroscopy using synchrotron radiation and high-resolution transmission electron microscopy. The experiments showed that metal nanoparticles were mostly stabilized at defect sites of the FLG support in the absence of oxygen functionalities. Catalytic properties of the samples were tested in CO oxidation reaction. For Pt nanoparticles forming agglomerates an oscillatory behavior under catalytic reaction conditions was observed for the first time for metal–graphene catalysts.     

Chemical Knockdown of MicroRNA with Small-Molecule Chimeras

This concept article introduces the emerging area of small-molecule chimeras (SMCs) for knocking down microRNAs (miRNAs), which are endogenous gene silencers involved in diverse pathological processes. Compared with agents for genetic knockdown, small-molecules hold significant promise in this field due to their ideal pharmacokinetic and pharmacodynamic properties. The SMCs introduced here are hetero-bifunctional molecules comprising small-molecule binders (SMBs) of miRNAs and chemical functionalities that either directly cleave RNAs or recruit ribonucleases to destroy RNAs. Binding of SMBs to miRNAs brings SMCs’ chemical functionalities close to the miRNA, eventually causing miRNA degradation. Compared with parent SMBs, SMCs exhibit remarkably enhanced potency and specificity in miRNA inhibition. The development and application of SMCs for miRNAs will be discussed.     

Expanding the catalytic repertoire of DNAzymes by modified nucleosides

Modified nucleoside triphosphates (dNTPs) are a versatile platform for the generation of high-density functionalized nucleic acids. The enzymatic polymerization of dNTPs allows the introduction of sensible functionalities that might not be compatible with the standard automated synthesis of oligonucleotides. Their application to in vitro selections, an elegant chemical approach to Darwinian evolution, delivers modified aptamers and catalytic nucleic acids with potentially enhanced properties. This review article highlights some recent synthetic examples of dNTPs bearing functionalities that are either found in the active site of protein enzymes or have been employed in organocatalysis and further underscores their usefulness in the development of some modified catalytic nucleic acids with special emphasis on M(2+)-independent RNA-cleaving DNAzymes.     

Reliability of Thermal Energy Storage Technologies

Thermal energy storage is considered an important element of future energy systems. However, it is mandatory that the storage technologies work reliably. More complex systems are usually more prone to failure. As system size increases and functionalities can be separated, a more differentiated analysis is necessary. Large-scale applications often involve intrinsic redundancy because scale-up to some extent is realized through numbering-up. Therefore, failures of individual components do not cause total outage of the thermal energy storage, but only a certain loss in performance. A special feature of some thermochemical storage technologies is that separate parts of the whole system provide the functionalities of charging and discharging. Consequently, many failure modes do not cause a complete loss of functionality, but only of one of the two functionalities.     

Synthesis and characterization of maleimide and norbornene functionalized benzoxazines

Two types of monofunctional benzoxazines with imide functionalities have been synthesized for improved thermal properties. These materials achieve char yields above 55% and exhibit glass transition temperatures above 250 °C. The new benzoxazines have maleimide and norbornene functionalities that can further polymerize with mechanisms different from benzoxazine. The multiple polymerization mechanisms of the maleimide based benzoxazine monomer with different free radical initiators are monitored by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The extent and type of polymerization, which affect the final network structure of the benzoxazine polymer, are characterized.     

Synthesis and characterization of microphase separated primary amine functionalized polystyrene-b-poly(2-vinylpyridine)

Microphase separated block copolymers containing primary amine functionalities would have applications in sensors, templates, anti-microbial surfaces and cell scaffolds. Primary amines allow for a variety of different click chemistries that facilitate these applications. In this investigation microphase separated polystyrene-b-poly(2-vinylpyridine) films were quaternized with a primary amine functionality utilizing the less common trimethylsilyl protecting group and a substitution reaction. The glass transition of the 2-vinylpyridine block was suppressed after functionalization. The newly introduced amine functionalities are susceptible to cross-linking through the use of glutaraldehyde, demonstrating the availability of the amines for further chemical modification. The trimethylsilyl protecting group allowed for the reliable quaternization of PS-b-P2VP with a primary amine, without disrupting the film or its morphology.     

Using oxidation to increase the electrical conductivity of carbon nanotube electrodes

Recent studies have demonstrated that significantly low sheet resistance (Rs) (<100 Ω/sq; comparable to ITO) were achieved in single-walled carbon nanotube (SWCNT) films treated with HNO₃ followed by thionyl chloride. Here we show that H₂SO₄ can effectively reduce the Rs of SWCNT electrodes. H₂SO₄ treatment generates defects (COOH and SO₃H functionalities) on SWCNTs and the produced chemical functionalities are beneficial for enhancing the electrical conductivity in SWCNT electrodes. It is plausible that the H₂SO₄p-dopes the SWCNTs and the attachment of chemical functionalities helps to stabilize p-doping owing to their electron-deficient property.     

Synthesis and characterization of telechelic macromers containing fatty acid derivatives

Telechelic macromers end-capped with (meth)acrylic functionalities are the most commonly used materials in rigid, dental formulations. In order to provide higher flexibility to the final product (not necessarily for dental applications), long chain aliphatic fatty acid derivatives may be chosen. Thus, new telechelic macromers comprising methacrylic functionalities and dimer fatty acid derivatives have been synthesized for the first time, and their chemical structure is discussed in detail. Six different systems comprising ester, anhydride and urethane bonds were synthesized from non-toxic raw materials. FTIR spectroscopy and NMR analysis were used to evaluate chemical structure of new systems. Their molecular masses were estimated from GPC measurements and from an analytical method based on iodine value determination. The latter one proved to be very accurate in determining molecular masses of methacrylated telechelics according to a new method developed in this work. We demonstrated that, via simple organic chemistry, different architectures of telechelic macromers comprising commercially available, long chain derivatives of fatty acid, mainly linoleic acid, with α,ω-dihydroxy, α,ω-dicarboxy or α,ω-diamino functionalities were successfully synthesized. These macromers facilitate the development of new reactive (preferably, photocurable) flexible systems for potential biomedical applications.     

Chemical derivatization of Athabasca oil sand asphaltene for analysis of hydroxyl and carboxyl groups via nuclear magnetic resonance spectroscopy

Athabasca oil sand asphaltene was methylated with different base catalyst/solvent combinations in order to find an optimum procedure for analysis of the number and types of hydroxyl and carboxyl functional groups. High resolution carbon-13, fluorine-19, and silicon-29 NMR spectra were used to monitor the degree of methylation, trifluoroacetylation, trimethylsilylation, and aromaticity of asphaltene. Tetra-n-butylammonium hydroxide as phase transfer base catalyst and tetrahydrofuran or dichloromethane as solvent result in enhanced O-methylation of asphaltene. At least two types of acidic oxygen containing functionality have been detected, viz. hydroxyl and carboxyl (aliphatic and aryl). On average there are few, ≤4-8, hydroxyl containing groups (including COOH) per asphaltene molecule. ¹³C NMR lineshapes suggest a broad asymmetric distribution of acidic sites. The NMR and elemental analyses allow for oxygen containing functionalities to be included in an average molecular structure. A sludge phase collected from aqueous and hydrochloric acid extractions of asphaltene has also been analyzed. A correlation is observed between the degree of O-methylation and the dielectric permittivity of the solvent and the acidity of the substrate reaction site.     

Polyurethane networks from polyols obtained by hydroformylation of soybean oil

BACKGROUND: Vegetable oil‐based polyols are a new class of renewable materials. The structure of oil‐based polyols is very different from that of petrochemical polyols, and it is closely related to the structure of oils. The objective of this work was to analyze the structural heterogeneity of soy‐based polyols and its effect on the properties of polyols and polyurethanes. RESULTS: A series of polyols with a range of hydroxyl numbers were prepared by hydroformylation and partial esterification of hydroxyls with formic acid. Polyols were reacted with diphenylmethane diisocyanate to obtain polyurethanes of different crosslinking density. Gelation was simulated using the Monte Carlo method with a calculated distribution of functionalities for each polyol. CONCLUSIONS: Most polyols are powerful crosslinkers since weight average functionality varied from 5 to 2.5 resulting in gel points from 53 to 83% conversion. Heterogeneity of polyols had a negative effect on mechanical properties of rubbery polyurethanes and this should be taken in account when designing polyols for flexible applications. This effect was not pronounced in glassy polyurethanes. Copyright © 2007 Society of Chemical Industry     

Oxidatively induced abstraction reactions. A synthetic approach to low-coordinate and reactive early transition metal complexes containing metal-ligand multiple bonds

A library of low-coordinate titanium and vanadium complexes containing terminal metal-ligand multiply bonded functionalities such as alkylidenes, alkylidynes, and imides have been prepared by one-electron oxidatively induced alpha-hydrogen abstraction reactions. In the case of the alkylidene motif, the nucleophilic nature of the M-C multiple bond permits subsequent reactions such as alpha-hydrogen migration to generate other rare functionalities such as phosphinidene-alkyl and imide-alkyls. Identifying and fine-tuning of the supporting ancillary ligand on the metal has allowed the isolation of kinetically stable titanium alkylidene and phosphinidene systems. The former is a key functionality to generate transient titanium alkylidynes, which readily engage in intermolecular C-H activation reactions of arenes and alkanes, and the ring-opening metathesis of aromatic substrates such as pyridines. In this Account, we describe several synthetic strategies to achieve reactive functionalities, functionalities that were previously portrayed as "incompatible" or "too kinetically reactive" with 3d early transition metals.     

Examination of the double-layer capacitance of an high specific-area C-cloth electrode as titrated from acidic to alkaline pHs

The titration of the interfacial capacitance of a C-cloth electrochemical capacitor electrode was undertaken for the purpose of evaluating the cyclic voltammetry (CV) responses as a function of the pH of an aqueous electrolyte over the range of 0–14. As the pH was increased from 0 (aqueous H₂SO₄) to a progressively more alkaline (NaOH) solution of pH 11, a 30% loss in capacitance is seen, partly attributable to the disappearance of the pseudocapacitive peaks based on the oxidation/reduction of the surface quinone groups. As the pH is increased above 11, the capacitance increases ca. 20%, as other surface functionalities (a pyrone derivative and another unknown species) become activated in alkaline solution. When the C-cloth is titrated from pHs of 14 to 2, the CV current profile shrinks (with a concomitant decrease in charge-storage capacity). However, at electrolyte pHs below ca. 2, the quinone functionalities are activated and the charge-storage capacity increases ca. 30% above the initial value. It was found that the CV current responses in pH 14 electrolytes are smaller when the titration is base-initiated, rather than acid-initiated, due to an activation step required to make the pyrone functionalities active in alkaline solution.     

Droplet microfluidic networks as hybrid dynamical systems: Inlet spacing optimization for sorting of drops

The ability to manipulate drops is essential for integrating multiple processes in droplet microfluidics-based lab-on-a-chip devices. Examples of such droplet manipulation operations include sorting, sequencing, synchronization, and so forth. Microfluidic networks are promising platforms for performing these functionalities. This work explores the design of entry times of drops, a set of operating parameters, in a microfluidic network to achieve a desired functionality. Here, we specifically focus on sorting of drops at the exit of the network. For the first time, droplet microfluidic networks are perceived as hybrid dynamical systems. This viewpoint allows us to develop a methodology for designing the entry times of drops in microfluidic networks to achieve desired functionalities through the notion of constraint satisfaction. The solution to this constraint satisfaction problem provides entry times that result in the desired functionality. The proposed method allows one to establish the existence/nonexistence of entry time solutions for a desired functionality.     

Atom-Transfer Radical Polymerisation (ATRP) as a Tool for the Development of Optical Sensing Phases

The advantages of atom-transfer radical polymerisation (ATRP) for synthesising well-defined polymers have made this technique very popular in recent years for the synthesis of new polymers and copolymers with optical properties. The components involved in ATRP and their effect on composition, functionalities and topology have been reviewed according to the optical properties of the obtained (co)polymers. Because several functionalities and architectures can be combined in ATRP, this technique is a useful tool for the synthesis of new (co)polymers specially designed to meet the requirements of the sensor setup.