Cyclo- and cyclized diene polymers. XVI. Nature of the active species and a proposed mechanism of cyclopolymerization of isoprene with catalysts containing ethylaluminum halides

The polymerization of isoprene with C₂H₅AlCl₂ to yield solid cyclopolyisoprene is markedly accelerated by the addition of TiCl₄. The polymer yield passes through a maximum on increasing the catalyst reaction time with or without monomer present. The active species are probably cations formed by dissociation of the reaction product of C₂H₅AlCl₂ and TiCl₄. The polymerization of isoprene with (C₂H₅)₂AlX–TiCl₄ (X = F, Br, Cl) has maximum activity at an Al/Ti mole ratio of 0.75 corresponding to conversion of R₂AlX to RAIX₂ which then reacts with remaining TiCl₄. A proposed mechanism of cyclopolymerization of conjugated dienes involves monomer activation, i.e., conversion to cation radical by one-electron transfer to catalyst cation which is itself neutralized, addition of cation end of monomer cation radical to terminal or internal unsaturation of fused cyclohexane polymer chain, one-electron transfer from “neutral” catalyst to cation on polymer chain which is then transformed to a diradical which undergoes coupling to form a cyclohexene ring. The mechanism of the “living” polymerization involves addition of catalyst-activated monomer to a “dead” polymer with a terminal cyclohexene ring and regeneration of the active catalyst.     

Quasiliving Carbocationic Poiymerization. III. Quasiliving Polymerization of lsobutylene

The polymerization of isobutylene has been investigated by the use of the steady, slow, continuous monomer addition technique in the presence of a variety of initiating systems, i.e., “H₂O”/TiCl₄, “H₂O”/AlCl₃, C₆H₅C(CH₃)₂Cl/TiCl₄, p-ClCH₂ C₆(CH₃)₄* CH₂Cl/AlCl₃ at -50°C. Quasiliving polymerizations have been obtained with the “H₂O” and C₆H₅(CH₃)₂Cl/TiC1₄ systems in 60/40 v/v n-hexane/methylene chloride solvent mixtures with very slow monomer input. After a brief “flash” polymerization, the M _n of PIB increased linearly with the cumulative amount of monomer added (consumed); however, the number of polymer molecules formed also increased, indicating the presence of chain transfer to monomer. With the “H₂O”/TiCl₄ initiating system, M _n,max was 56,000 and M _w /M _n < 2.0. By the use of the C₆H₅C(CH₃)₂CL/TiCl₄ initiating system, quasiliving polymerization has been achieved and chain transfer could virtually be eliminated.     

Die Kristallstruktur des „supramolekularen”︁ Cadmiumcyanid-Hexamethylentetramin-Addukts [Cd(CN)2 · 2/3 C6H12N4]

The Crystal Structure of the “Supramolecular” Cadmiumcyanide-Hexamethylenetetramine Adduct [Cd(CN)₂ · 2/3 C₆H₁₂N₄] Single crystals of a new compound in the system Cd(CN)₂-hexamethylenetetramine (HMTA) with the composition [Cd(CN)₂ · 2/3 C₆H₁₂N₄] were obtained by crystallization from an aqueous solution containing Cd(CN)₂ and HMTA. The structure consists of a ?supramolecular”? network of ? Cd? CN? Cd- and ? Cd? HMTA? Cd-chains. The structure is compared with that of an already known compound [Cd(CN)₂ · 1/3 C₆H₁₂N₄].     

On the mechanism of the ion-molecule reaction CH3+ + CH4 = C2H5+ + H2

Experimental evidence supporting the “direct” reaction model and the “intermediate complex” model for the reaction CH₃⁺(CH₄, H₂)C₂H₅⁺ are analysed. It is shown that the evidence for the former can equally well be interpreted in terms of a proposed model of persistent complex formation and decay. The plausibility of a “direct” mechanism is discussed and is found to be poor.     

Novel fluorescent supramolecular polymer metallogel based on Al3+ coordinated cross-linking of quinoline functionalized- pillar[5]arene act as multi-stimuli-responsive materials

A novel supramolecular polymer metallogel ( QP5-AlG ) has been constructed by cross-linking of bis-8-hydroxyquinoline functionalized pillar[5]arene with Al³⁺. The metallogel QP5-AlG shows light blue aggregation induced emission (AIE) in DMSO/H₂O binary solution. Interestingly, the QP5-AlG shown multiple external stimuli-responsive behaviors such as temperature, guest compounds, acid, base and so on. The QP5-AlG can be used as a fluorescent material for detection of Fe³⁺, F^-, trifluoroacetic acid (TFA) and triethylamine (TEA) by different fluorescence states (“on” or “off”). The (limits of lowest detection) LOQs of the QP5-AlG for Fe³⁺, F^-, TFA and TEA are in the range of 4.39 × 10^-9-1.82 × 10^-7 M. More interestingly, a QP5-AlG -based rewritable and erasable fluorescent platform was demonstrated, which offers a potential testbed for performing “write-erase-write” cycles multiple times. This study provides insight into the development of novel multifunctional supramolecular materials.     

On the HALA effect in the NMR carbon shielding constants of the compounds containing heavy p‐elements

The heavy atom (HA) effect on the NMR isotropic carbon shielding constants is computationally investigated in the series of model ethanes, ethylenes, and acetylenes, C_βH₃? C_αH₂? XH_n, C_βH₂? C_αH? XH_n, C_βH?C_α? XH_n (n = 0, 1, 2, or 3 depending on X), where X covers p‐elements in the 13–17 groups of the 3–6 periods in as many as 60 compounds. Compounds under study provide diverse bonding situations for the α‐ and β‐carbons, which are characterized by the consecutive increase of the s‐character of the C_β? C_α and C_α? X bonds, being one of the factors influencing spin‐orbit part of the HA on light atom effect (SO‐HALA). The “chalcogen dependence,” “pnictogen dependence,” “tetrel dependence,” and “triel dependence” are established for the 16th, 15th, 14th, and 13th groups, respectively. A well‐known “normal halogen dependence” for the ¹³C NMR chemical shifts, established much earlier for the compounds containing 17th group elements, also revealed itself in all three series under investigation. The dependence of the spin‐orbit effects size depending on the number of the lone electron pairs (LEPs) on HA X has also been investigated. The comparison of theoretical ¹³C NMR chemical shifts with experiment is performed for three representative tellurides. The HALA effect in this series has been shown to be strongly dependent on the number of tellurium LEPs.     

Hydrogen‐bonded assemblies in the molecular crystals of 2,2′‐thiodiacetic acid with ethylenediamine and o‐phenylenediamine

Carboxylate molecular crystals have been of interest due to the presence of hydrogen bonding, which plays a significant role in chemical and crystal engineering, as well as in supramolecular chemistry. Acid–base adducts possess hydrogen bonds which increase the thermal and mechanical stability of the crystal. 2,2′‐Thiodiacetic acid (Tda) is a versatile ligand that has been widely explored, employing its multidendate and chelating coordination abilities with many metals; however, charge‐transfer complexes of thiodiacetic acid have not been reported. Two salts, namely ethylenediaminium 2,2′‐thiodiacetate, C₂H₁₀N₂²⁺·C₄H₄O₄S₂²⁻, denoted Tdaen, and 2‐aminoanilinium 2‐(carboxymethylsulfanyl)acetate, C₆H₉N₂⁺·C₄H₅O₄S⁻, denoted Tdaophen, were synthesized and characterized by IR, ¹H and ¹³C NMR spectroscopies, and single‐crystal X‐ray diffraction. In these salts, Tda reacts with the aliphatic (ethylenediamine) and aromatic (o‐phenylenediamine) diamines, and deprotonates them to form anions with different valencies and different supramolecular networks. In Tdaen, the divalent Tda²⁻ anions form one‐dimensional linear supramolecular chains and these are extended into a three‐dimensional sandwich‐type supramolecular network by interaction with the ethylenediaminium cations. However, in Tdaophen, the monovalent Tda⁻ anions form one‐dimensional zigzag supramolecular chains, which are extended into a three‐dimensional supramolecular network by interaction with the 2‐aminoanilinium cations. Thus, both three‐dimensional structures display different ring motifs. The structures of these diamines, which are influenced by hydrogen‐bonded assemblies in the molecular crystals, are discussed in detail.     

Syntheses,crystal structures,and characterization of seven coordination compounds based on flexible 1,1′-(1,4-butanediyl)bis(3-carboxyl-2-oxidopyridinium)

Seven coordination compounds based on 1,1′-(1,4-butanediyl)bis(3-carboxyl-2-oxidopyridinium), [CoNa(L)_1.5(C₂H₅OH)₃] (1), [Zn(L)(OH)₂]?·?4H₂O (2), [Co(L)(OH)₂]?·?2H₂O (3), [Co(L)(H₂O)] (4), [Zn(L)(H₂O)] (5), [Ni(L)(H₂O)] (6), and [Mn(L)(H₂O)] (7), have been synthesized and crystal structures have been determined by single-crystal X-ray diffraction. Compound 1 exhibits a 0-D molecular structure. Compound 2 shows a 1-D “Z” chain structure. Neighboring chains are further linked by hydrogen-bonding interactions into a 2-D supramolecular layer. Compound 3 features a 1-D “Z” chain structure. The chains are further extended into a 2-D supramolecular structure by hydrogen-bonding interactions. Compounds 4–7 are isomorphous and display 2-D (4⁴)-SQL networks. These compounds are further characterized by infrared spectra, elemental analyses, and X-ray powder diffraction. The luminescent properties of the compounds were also investigated.     

Design of TiO2@graphene nanosheets with rough surface and its reinforcement to polyarylene ether nitriles

The interfacial interaction is extremely important when dealing with filler‐reinforced polymer materials. Herein, in order to improve the interfacial interaction with the polyarylene ether nitriles (PEN) matrix, a three‐dimensional rough structure was designed. First, needle‐like TiO₂ nanocrystals were grown on each surface of the graphene. Morphology analysis proved that rough TiO₂ nanocrystals were coated on the graphene nanosheets. Then, TiO₂@graphene/PEN composites were fabricated to investigate the filler–matrix interaction. Thereafter, the different polymer chains could be interlocked by the TiO₂ “needles” when the rough TiO₂@graphene was embedded into the polymer resin. The surrounding PEN polymer chains (work as ropes) could tie to the “needles” (work as wood pile). That is to say, the effective polymer chain length was greatly lengthened, resulting in the improvement of interfacial interactions and mechanical properties. Most importantly, the morphology, mechanical and rheological tests of the composites also proved the improvement of interfacial interactions and mechanical properties. Copyright © 2015 John Wiley & Sons, Ltd.     

Influences of ClH and BrH on the pyrolyses of neopentane and ethane at small extents of reaction

A symbolic mechanism “μH, YH” has been proposed to account for the homogeneous chain pyrolysis of an organic compound μH in the presence of a hydrogenated additive YH at small extents of reaction. An analysis of this mechanism leads to two limiting cases: the thermal decomposition of neopentane corresponds to the first one (A), that of ethane to the second one (B). Previous experimental work has shown that this mechanism seems to account for a number of experimental observations, especially the inhibition of alkane pyrolyses by alkenes. Experimental investigations were extended by examining the influences oftwo hydrogen halides (ClH and BrH) upon the pyrolyses of neopentane (at 480°C) and ethane (around 540°C). The experiments have been performed in a conventional static Pyrex apparatus and reaction products have been analyzed by gas-liquid chromatography. The study shows that ClH and BrH accelerate the pyrolysis of neopentane (into i-C₄H₈ + CH₄). The experimental results are interpreted by reaction schemes which appear as examples of the mechanism “μH, YH” in the first limiting case (A). The proposed schemes enable one to understand why the accelerating influence of ClH is lower or higher than that of BrH, depending on the concentration of the additive. An evaluation of the rate constant of the elementary steps neo-C₅H₁₁ · → i-C₄H₈ + CH₃ · is discussed. In the case of ethane pyrolysis, BrH inhibits the formation of the majorproducts (C₂H₄ + H₂) and, even more, that of n-butane traces. The experimental results are interpreted by a reaction scheme which appears as an example of the mechanism “μH, YH” in the second limiting case (B). On the contrary, ClH has no noticeable influence on the reaction kinetics. This result inessentially due to the fact that the bond dissociation energy of Cl? H(?103 kcal/mol) is higher than that of C₂H₅—H (?98 kcal/mol), whereas that of Br—H (?88 kcal/mol) is lower.     

Some elastic and thermoelastic properties of two organophosphazene polymers

Samples of the alkoxyphosphazene polymer [P(OCH₃)₂? N? ]_x and the aryloxyphosphazene polymer [P(OC₆H₅)(O-p-C₆H₄C₂H₅)? N? ]_x were crosslinked using γ-radiation. The resulting elastomeric networks were characterized, in elongation, with regard to both their stress-strain relationships and their stress-temperature (“thermoelastic”) properties. Values of the ratio 2C₂/2C₁ of Mooney–Rivlin constants used to characterize the stress-strain isotherms were found to be similar to those of other elastomeric networks of comparable degree of crosslinking. The thermoelastic data show the energetic component of the retractive force to be positive for the alkoxy polymer, but negative for the aryloxy polymer. Although it is not difficult to suggest a possible molecular explanation for some of these thermoelastic results, a definitive interpretation would require reliable information on the conformational characteristics of the skeletal bonds in the polyphosphazene chain.     

Plasma- and vacuum-ultraviolet (VUV) photo-polymerisation of N- and O-rich thin films

Nitrogen (N)- and oxygen (O)-rich organic thin films were deposited by vacuum-ultraviolet (VUV)-assisted photo-chemical polymerisation of flowing ethylene (C₂H₄)–ammonia (NH₃) and C₂H₄–nitrous oxide (N₂O) mixtures of varying ratios, R, respectively. The reaction mechanism of these binary gas mixtures was investigated as a function of the wavelength, λ, of two near-mono-chromatic VUV sources. Surface-near compositions of these “UV-PE:N” and “UV-PE:O” films were determined by X-ray photoelectron (XPS), and by Fourier transform (reflection–absorption) infrared (FTIR) spectroscopies. The two types of films were compared with plasma polymers deposited using low-pressure radio-frequency (r.f.) glow discharges in similar gas flow mixtures, “PPE:N” and “PPE:O”. VUV-photochemistry appears to be superior to plasma-chemistry in its capability to produce nearly “mono-functional” organic thin films, ones that are rich in primary amines, –NH₂, and in carboxylic acid groups, –COOH, respectively.     

Some novel triorganotin(IV) derivatives of β, δ-triketones

Thirty triorganotin(IV) derivatives of the type R₃Sn(R′COCHCOCH₂COR″) and [R₃Sn]₂ (R′COCHCOCHCOR″) (where R = CH₃, C₂H₅, nC₃H₇, nC₄H₉ and C₆H₅ and R′ = R″ = CH₃, C₆H₅ or R′ = C₆H₅, R″ = CH₃) have been synthesised by the interaction of R₃SnCl with mono- or disodium salt of 2, 4, 6-heptanetrione, 1-phenyl-1, 3, 5-hexanetrione and 1, 5-diphenyl-1, 3, 5-pentanetrione in 1:1 and 2:1 molar ratios, respectively. The complexes have been examined by their molecular weight, IR, PMR and elemental analyses and their tentative structures assigned. Both “Z” and “E” forms have been identified in the 1:1 complexes in equilibrium with the enol form containing five coordinate tin. The 2:1 derivatives contain one five- and other four coordinated tin(IV) except the phenyl analogue where both the tins are five coordinated.     

Hartree—Fock—Slater-LCAO studies of the acetylene—transition metal interaction. III. Binding to mono- and dinuclear Ni complexes with carbonyl and isocyanide ligands

The bonding of C₂H₂ in the nickel complexes [π-(C₂H₂)Ni(CO)₂], [π-(C₂H₂)Ni(CNH)₂] and [μ₂-(C₂H₂) {NI(CNH)₂}₂] has been studied by the non-empirical self-consistent Hartree—Fock—Slater-LCAO method. Calculations have been performed, not only for these complexes, but also for free C₂H₂ and its substituted analogues, propyne, but-2-yne and hexafluorobut-2-yne, and for the mono- and dinuclear complex fragments, [Ni(CNH)₂] and [{NI(CNH)₂}₂], which interact with the C₂H₂ molecule. The main difference with nickel surfaces, which have analogous π and μ₂ adsorption sites for C₂H₂ that we have studied by the same method, is the much stronger 3d, 4s, 4p hybridization induced by the CNH and CO ligands. In the bis(diisocyanide—nickel) complex these hybrids form a rather broad dsp “band”. The low lying occupied levels in this “band” cause a strong interaction with the filled acetylene π_u orbitals which dominates the π to metal donation effect. In the mononickel—acetylene complex this donation does occur, however, just as for acetylene adsorbed on nickel surfaces (in combination with the more prominent metal to π^* back donation which we find in all cases). A linear relation has been derived between the CC stretch frequencies in coordinated C₂H₂ molecules and the calculated CC overlap populations. Substitutio of the H atoms in (free) C₂H₂ by CH₃ or CF₃ groups has almost no effect on the CC overlap population and force constant.     

Zirconia-based amperometric sensor using ZnO sensing-electrode for selective detection of propene

The sensing characteristics to propene (C₃H₆) were examined at 600 °C under wet condition for the amperometric sensor using a yttria-stabilized zirconia (YSZ) tube and ZnO (+8.5 wt%Pt) sensing-electrode (SE). In order to improve the sensitivity to C₃H₆, the “pulsed-potential method” was adopted here. It was found that the current response varied almost linearly with C₃H₆ concentration in the range of 0–200 ppm when SE was polarized at +1.0 V (vs. Pt/air reference electrode) for a period of 0.3 s. By using the present “pulsed-potential method”, the sensitivity to 100 ppm C₃H₆ was increased about 1000 times, compared with the normal “constant-potential method”. The excellent selectivity to C₃H₆ was also obtained for the present sensor without influence of other hydrocarbons, NO_x, CO, H₂, etc.     

Self-assembly of supramolecular Ni(II) and Cu(II) metalmacrocyclic compounds with tetraazamacrocyclic ligand into a gelatin-immobilized matrix

Self-assembly in M(II)-ethanedithioamide [H₂N–C(=S)–C(=S)–NH₂]-propanone triple systems (M=Ni, Cu) into corresponding metal(II) hexacyanoferrate(II) gelatin-immobilized matrix systems under contact with aqueous-alkaline (pH?～?12) solutions containing ethanedithioamide and propanone have been studied. Formation of supramolecular macrotetracyclic compounds of Ni(II) and Cu(II) with 2,7,7,9,14,14-hexamethyl-3,6,10,13-tetraazacyclotetradecadien-2,9-tetrathione-4,5,11,12 containing original “kernel” (metal complex) and “shell” surrounding this “kernel”, of polypeptide chains of the gelatin molecules, occurs under such specific conditions.     

A theoreticalab initio study of the reaction of formation of 2-fluoroethanol from oxirane and HF

The reaction of ring opening of epoxides under the action of a halogenic acid has been investigated using as model the system C₂H₄O + HF → CH₂OHCH₂F. The physical conditions chosen for the model more directly correspond to the gas phase reaction and under these conditions the preferred mechanism leads to the formation of a halohydrine having the same configuration at the C atom as the reagent. Parallel investigations have been performed on other mechanisms which postulate the preliminary formation of the conjugate acid of the oxirane (C₂H₄OH⁺) and proceed via the well known mechanismsA ₁ orA ₂. In this case the best mechanism corresponds to the so-called “borderlineA ₂” mechanism. This last type of mechanism probably is the dominant one in protic solutions, but by coupling the present calculations with experimental conductometric measurements in anhydrous aprotic media one could consider the first concerted mechanism as a possible candidate also for the reaction in “inert” media. A qualitative analysis of the transition state indicates, in addition, that the propension for the retention path, is probably emphasized by the use of HF as reactant, and that with other acids, like HC1, or even by assuming the presence of dimers like HF·HF, the inversion path could be preferred. The investigations have been done by determining the geometry of the transition state and the reaction coordinate withab initio SCF STO-3G calculations on the whole nuclear configuration space (21 dimensions). These calculations have been supplemented by a few CI calculations on the same basis set and by a few SCF calculations with a larger basis set.     

Wellenmechanische Absolutrechnungen an Molekülen und Atomsystemen mit der SCF?MO?LC(LCGO) Methode. V. Bindungsbeteiligung der Inneren Elektronen des C-Atoms

Using the results of ab initio calculations, by comparison of the “1s orbital energies” of the C atom in the compounds C₆H₆, C₅H, C₃H₆ (cyclopropane), C₂H₄ as well as at the C atom itself the bond electrons were found to have a significant influence on the inner electrons. The reason for this is pointed out and an explanation is given. The connection between the bonding and this “1s orbital energy” change as well as the importance of this result for quantum-chemical “models” is discussed.     

Low-Pressure Plasma Polymerization of Acetylene–Ammonia Mixtures for Biomedical Applications

Past research in this laboratory has focused on the deposition of nitrogen- (N)-rich thin organic coatings for biomedical applications; among usual fabrication methods are plasma polymerization (PP) at low- (“L”) or atmospheric- (high-, “H”)-pressure. In the “L” case, ethylene (“E”, C₂H₄)/ammonia (NH₃) feed-gas mixtures with different flow ratios, R, are used, by which the nitrogen- and primary amine concentrations, [N] and [–NH₂], respectively, can be reproducibly controlled. The generic symbol we use for that family of deposits is L-PPE:N. In the present research, we used acetylene (“A”, C₂H₂) as the hydrocarbon feed, because our earlier experience with “H”-type materials (H-PPE:N and H-PPA:N) revealed striking differences in physico-chemical (e.g. [N] and [–NH₂], and solubility) characteristics, which are important for applications. We now find that such differences also exist between the L-PPA:N and L-PPE:N families of coatings. This is attributed to the fundamentally different bonding structures of “A” and “E”, namely CH≡CH and CH₂=CH₂; the former leads to more highly cross-linked, [NH₂]-leaner deposits, as was also noted for the “H”-type deposits mentioned above.