Icosahedron cage occupancy of structure-H hydrate helped by Xe -1,1-, cis -1,2-, trans-1,2-, and cis-1,4-dimethylcyclohexanes

Four mixtures of 1,1-, cis-1,2-, trans-1,2-, and cis-1,4-dimethylcyclohexanes (hereafter abbreviated DMCH) including H₂O and Xe have been investigated in a temperature range over 274.5 K and a pressure range up to 2.7 MPa. The 1,1-DMCH and cis-1,2-DMCH generate the structure-H hydrate in the temperature range up to 295.2 and 280.2 K, respectively. Especially, very large depression of equilibrium pressure has been observed in the structure-H 1,1-DMCH hydrate system. On the other hand, neither trans-1,2-DMCH nor cis-1,4-DMCH generates the structure-H hydrate in the present temperature range. It is an important finding that the cis-1,4-DMCH does not generate the structure-H hydrate in the presence of Xe, while the mixture of cis-1,4-DMCH and methane generates the structure-H hydrate.     

Tuning of the neutral state color of the π-conjugated donor-acceptor-donor type polymer from blue to green via changing the donor strength on the polymer

Two donor-acceptor-donor types of π-conjugated monomers were synthesized using Stille coupling reaction. Both monomers were found to produce electroactive polymers upon electrochemical oxidation. The effects of different donor substituents on the polymers' electrochemical and spectroelectrochemical properties were examined. Optical characterization revealed that the band gaps of poly(2-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-7-yl)-5,8-di(thiophen-2-yl)quinoxaline) (PDBQTh) and poly(2-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-(2,3-dihydrobenzo[b][1,4]dioxin-7-yl)-5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-8-(2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)quinoxaline) (PDBQEd) were 1.5 eV and 1.3 eV, respectively. PDBQEd reveals two distinct absorption bands as expected for this type of donor-acceptor-donor polymer at 423 and 738 nm, while PDBQTh has a single absorption band at 630 nm. The colorimetry analysis revealed that while PDBQTh has a blue color, PDBQEd showed a green color in the neutral state. PDBQEd revealed reversible n-doping.     

Selective Hydrogenation of 2-Butyne-1,4-diol to 1,4-Butanediol Over Particulate Raney® Nickel Catalysts

The current study describes the results on the selective hydrogenation of the 2-butyne-1,4-diol to 1,4-butanediol over Raney^® nickel catalysts both in batch and in CSTR mode. The detailed kinetic analysis of the reaction in batch mode revealed the existence of three characteristic regions. In the first region, A, the starting 2-butyne-1,4-diol produces primarily cis-2-butene-1,4-diol. In the second region, B, the dominant species is cis-2-butene-1,4-diol, which is either hydrogenated to 1,4-butanediol or isomerizes to trans-2-butene-1,4-diol. In the third region, C, the accumulated 4-hydroxybutanal is slowly hydrogenated to 1,4-butanediol. When the same reaction was carried out in a CSTR mode, the only products detected initially are the 1,4-butanediol and n-butanol. The first by-product detected immediately after the end of the first stage is the linear hemiacetal between the 4-hydroxybutanal with 1,4-butanediol. This species has been used as convenient tracer for determining the length of the selective region of the catalyst performance.     

Polybutadiene modified by epoxidation. 1. Effect of polybutadiene microstructure on the reactivity of double bonds

The reactivity of low-molecular weight sodium polybutadiene (1,2-PB) and n-butyllithium polybutadiene (1,4-PB) has been studied during epoxidation with peracetic acid. The effect of the epoxy groups formed on the polymer solution viscosity has also been investigated. It was found that the rate constant of 1,4-PB epoxidation is ～1.9 times greater than that for 1,2-PB of a similar molecular weight. The reactivity of various structural polymer unit forms was studied by spectroscopic methods (i.r. and ¹H n.m.r.); it was found that reactivity depends on chain microstructure in the following way:for 1,2-PB: trans-1,4 >cis-1,4 ? 1,2for 1,4-PB: cis-1,4 >trans-1,4 ? 1,2An increase in the limiting viscosity number was observed with increasing epoxy content in the 1,2-PB chain, but the opposite effect was observed for 1,4-PB. The solubility parameter, δ, for both kinds of epoxy polybutadiene was found to be similar ($\text{19.8 × 10}{}^3\text{J}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{·}\text{m}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$).     

Synthesis and characterization of some polyurethane ionomers

Polyurethane ionomers based on either poly(propylene glycol), PPG, or poly(ethylene glycol), PEO, and di- (4-isocyanatophenyl) methane, MDI, butane-1,4-diol and cis-2-butene-1,4-diol have been synthesized and characterized. Attempts to convert the unsaturated polyurethanes directly to ionomers by reaction with N-chlorosulphonyl isocyanate, CSI, followed by hydrolysis, failed due to the more favoured reaction of CSI with the labile hydrogen on the urethane linkage. Therefore, the cis-2-butene-1,4-diol was first converted to the dibenzoate which was then treated with CSI to form the β-lactam derivatives. Subsequent hydrolysis of these derivatives with tetra-n-butyl ammonium hydroxide solution produced ionic derivatives whilst at the same time regenerating the terminal -OH groups. These ionic diol intermediates were then used for synthesizing the polyurethane ionomers.     

Poly(p-phenylene vinylene) derivatives with ester- and carboxy-functionalized substituents: a versatile platform towards polar functionalized conjugated polymers

A polar functionalized poly(p-phenylene vinylene) (PPV) derivative, ester containing poly(1,4-(2-(pentyloxy-5-carboxy methylester)-5-methoxyphenylene)vinylene), has been prepared via the sulfinyl precursor route. Subsequently, the carboxylic acid containing poly(1,4-(2-(5-carboxypentyloxy)-5-methoxyphenylene)vinylene) is readily obtained by the basic hydrolysis of the ester side groups. This carboxylic acid substituted polymer exhibits significantly improved optical properties as compared to previously reported similar polymers. To obtain polar functionalized PPV derivatives with more complex tailored substituents a versatile novel approach is presented based on the Mitsunobu reaction conditions via a post-polymerization functionalization of the carboxylic acid side groups. Using these reaction conditions substituents containing various ester groups, i.e. 4-nitrobenzyl, 2-nitrobenzyl, 5-(methyl)furfural and 3-N,N-dimethylamino-1-propane, have been covalently attached to the phenylene ring. Analytical data of the functionalized polymers are consistent with a quantitative functional group substitution. The results demonstrate that the employed functionalization method allows for the introduction of a large variety of polar substituents in a straightforward manner.     

Distribution of isomeric structures in polyisoprenes

The ¹³C-n.m.r. spectra of polyisoprenes were investigated. Polyisoprenes were prepared with $\text{n-Buli}\text{Et}{}_2\text{O}$, radical (emulsion polymerization), and Alfin catalysts. Poly(isoprene-4,4-d₂)s were also prepared with $\text{n-BuLi}\text{Et}{}_2\text{O}$ catalysts for the signal assignments. ¹³C-n.m.r. signals were assigned for dyad or triad sequences of cis-1,4-, trans-1,4-, and 3,4- units. Signals due to head-to-head (4,1-1,4) and tail-to-tail (1,4-4,1) linkages were also assigned. On the basis of signal assignments it was revealed that cis-1,4-, trans-1,4-, and 3,4-units were distributed almost randomly in $\text{n-BuLi}\text{Et}{}_2\text{O}$ catalysed polyisoprenes. It was confirmed that radical and Alfin polyisoprenes contained about 15% of each of head-to-head and tail-to-tail linkages. It was found that radical polyisoprene had cis-1,4- and trans-1,4-units distributed randomly along the polymer chain regardless of the head and tail arrangements.     

Metal dependent control of cis-/trans-1,4 regioselectivity in 1,3-butadiene polymerization catalyzed by transition metal complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine

Fe(III), Cr(III), Fe(II), Co(II) and Ni(II) chloride complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine have been synthesized and characterized along with single crystal X-ray diffraction. These complexes, in combination with MAO, have been examined in butadiene polymerization. The catalytic activity and regioselectivity are strongly controlled by metal center and cocatalyst (MAO/Co ratio dependent in the case of Co(II) complex). The activity decreases in the order of Fe(III) > Co(II) > Cr(III) ≈ Ni (II) complexes, in consistent with the space around the metal center. Polybutadiene with different microstructure content, from high trans-1,4 units (88-95% for iron(III) and Cr(III)), medium trans-1,4 and cis-1,4 units (55% and 35%, respectively, for iron(II)) to high cis-1,4 units 79% for Co(II) and 97% for Ni(II) can be easily achieved by varying of the metal center. In addition, mechanism speculation is also presented to elucidate the dependence of catalytic behaviors on metal and cocatalyst.     

Head-to-head polymers: 19. Chlorination of cis-1,4-polybutadiene

Chlorination of cis-1,4-polybutadiene (PB) has been studied in detail. It was found that chlorination must be carried out in an oxygen free atmosphere at polymer concentrations below 0.5%, and at temperatures below room temperature in mixed solvents with dichloromethane as the major component. In the initial stage of chlorine addition to the double bonds of cis-1,4-polybutadiene, block structures of chlorinated segments are formed. The chlorine addition to the cis-butadiene units was not stereospecific and the final chlorination product had nearly a 1:1 ratio of the threo- and erythro structure of the CHCICHCI-units. Microphase separation in partially chlorinated PB was observed by d.s.c., dynamic-mechanical measurement, and transmission electron microscopy. It was concluded that partially chlorinated PB, whose degree of chlorination was lower than 65 mole %, was composed of almost pure cis-1,4-PB domains and a separate phase which consists ofCH₂CHCICHCICH₂units with perhaps as much as 10% of cis-1,4-PB units incorporated in this phase. If the degree of chlorination is more than 90 mole % one phase exists.     

Metal-controlled assembly of coordination polymers: Structural variation from 2D parallel interpenetration to 3D CsCl-type topology

Two novel metal-organic frameworks [Cd₂(hdb)₂(1,4-ndc)₂]_n (1) and [Ni₃(Hhdb)₂(1,4-ndc)₄(H₂O)₂]_n (2) have been synthesized under the similar hydrothermal conditions (hdb = 1,1′-(1,6-hexanediyl)bis(imidazole) and 1,4-ndc = 1,4-naphthalenedicarboxylate). The polymers (1) and (2) show 2D parallel interpenetration and 3D CsCl-type topology, respectively, which are mainly affected by the differences of the metal centers.     

Two Cd(II) coordination polymers based on 3,6-bis(imidazol-1-yl)carbazole: Syntheses,structures and photocatalytic properties

Hydrothermal reactions of CdCl₂·2.5H₂O with 3,6-bis(imidazol-1-yl)carbazole (bmcz), 2-amine-1,4-benzenedicarboxylic acid (2-NH₂-1,4-H₂BDC) or 1,4-naphthalenedicarboxylic acid (1,4-H₂NDC) afforded two coordination polymers, [Cd(2-NH₂-1,4-BDC)(bmcz)]_n (1) and [Cd(1,4-NDC)(bmcz)]_n (2). Complexes 1 and 2 were characterized by elemental analysis, IR, powder X-ray diffraction, and single-crystal X-ray diffraction. 1 and 2 are isomorphic and exhibit 3D supermolecular structures. The solid state luminescent and optical properties of 1 and 2 at ambient temperature were also investigated. A comparative study on their photocatalytic activity toward the degradation of methylene blue in polluted water was explored.     

Synthesis of well defined amino telechelic cis-1,4-oligoisoprenes from carbonyl telechelic oligomers; first studies of their potentialities as polyurethane or polyurea materials precursors

Carbonyl telechelic cis-1,4-oligoisoprene (CTPI) obtained from high molecular weight polyisoprene through an oxidative chain cleavage reaction have been chemically modified. Thus, new well defined amino telechelic cis-1,4-oligoisoprenes have been obtained in a mass range of 1600-2300 g/mol according to two different pathways. The first approach involved a standard mesylate displacement by sodium azide followed by smooth reduction using triphenylphosphine. The second pathway implied a reductive amination sequence. Primary or secondary amine functions have thus been selectively obtained at both oligomer chain-ends depending on reaction conditions. Peculiar NMR experiments conducted on these functional oligomers confirmed a precise control of functionality during the chemical modification. Moreover, their abilities to react with toluene diisocyanate or bis(succinimidyl)carbonate have been investigated.     

Asymmetric addition of thiol to diene polymer in the presence of optically active amines as catalyst

The asymmetric addition reaction of thiolacetic acid or benzylmercaptan to diene polymer (natural rubber, cis- and trans-1,4-polyisoprene, _cis-1,4-polybutadiene, various styrenebutadiene copolymers and alternating acrylonitrile-butadiene copolymer) by optically active catalysts such as d-bornylamine ([α]d?45.2°), l-aspartic diethyl ester (?11.2°), l-aspartic dibutyl ester (?5.3°) were carried out in benzene at room temperature to 90°C. The optically active polymers were obtained from natural rubber and cis-1,4- and trans-1,4-polyisoprene, but were not obtained from cis-1,4-polybutadiene, styrene-butadiene copolymers, and butadiene-acrylonitrile copolymer. The [α]²⁵_D value of optically active derivatives was ?0.1° ～ ?1.0° (in benzene), and the optical rotatory dispersion curves were found to fit the simple Drude equation.     

Application of infra-red digital subtraction techniques to the microstructure of polychloroprenes: 1. Accentuation and assignment of bands due to structural irregularities

Infra-red digital subtraction techniques have been employed to accentuate and assign the bands associated with the structural irregularities present in predominantly trans-1,4- polychloroprenes. The spectral contribution of the trans-1,4- configuration was removed from the spectra of polychloroprenes synthesized at different temperatures revealing contributions due to cis-1,4-, 1,2- and 3,4- structural irregularities. In addition bands associated with end-groups were also observed. The results demonstrate the potential of infra-red digital subtraction techniques to determine, both qualitatively and quantitatively, relatively small concentrations of structural irregularities in polychloroprenes.     

Synthesis and characterization of naphthalene diimide/diethynylbenzene copolymers

A series of conjugated polymers has been synthesized by Sonogashira coupling of N,N′-bis(2-octyldodecyl)-2,6-dibromonaphthalene-1,4,5,8-bis(dicarboximide) and four para-diethynylbenzene derivatives: 1,4-diethynyl-2,5-dihexadecyloxybenzene, 1,4-diethynyl-2,5-bis(2-octyldodecyloxy) benzene, 1,4-bis(2-ethylhexyl)-2,5-diethynylbenzene, 1,4-diethynyl-2,5-bis(trifluoromethyl)benzene. The polymers display absorption maxima at wavelengths ranging from 530 nm to 654 nm with molar absorptivities ranging from ca. 4 to 7 × 10⁴ M^?1 cm^?1. The peak reduction potentials, determined by differential pulse voltammetry, for polymer films varied from ?0.93 to ?1.14 V vs. ferrocenium/ferrocene with the trifluoromethyl-substituted derivative being the most readily reduced. All four polymers exhibited electron transport characteristics in bottom-gate/top-contact field-effect transistors, showing average electron mobility values ranging from 1.4 × 10^?4 to 3.7 × 10^?3 cm² V^?1 s^?1.     

Asymmetric hydrodimerization of styrene by a chiral zirconium complex containing a tetradentate [OSSO]-type bis(phenolato) ligand

The chiral non racemic (Λ,R,R)-[OSSO]Zr(CH₂Ph)₂ (1a) activated by methylaluminoxane (MAO) and in presence of H₂ produces the chiral hydrodimer (S)-1,3-diphenylbutane with good selectivity respect to the achiral 1,4-diphenylbutane. The absolute configuration of the chiral dimer and the effect of the hydrogen pressure on the ratio between 1,3-diphenylbutane and 1,4-diphenylbutane give useful information about the regiochemistry and stereochemistry of insertion of the styrene into the Zr–H bond.     

Molecular dynamics simulation of cis-1,4-polybutadiene. 2. Chain motion and origin of the fast process

Molecular dynamics (MD) simulations of cis-1,4-polybutadiene in bulk amorphous state were performed to elucidate the origin of a fast relaxation process observed by quasielastic neutron scattering (QENS) measurements. The details of the torsional motion for each dihedral angle were investigated with the torsional auto- and cross-correlation functions for several temperatures in this study. Temperature dependence of the correlation between the torsional autocorrelation and cross-correlation functions is also evaluated. The origin of the fast process of cis-1,4-polybutadiene is found to be mainly the cooperative conformational transitions of two dihedral angles located at both sides of the CH₂-CH₂ bond when the bond is in the trans conformation. The cooperative conformational transitions exhibit even below the glass transition temperature of cis-1,4-polybutadiene. The cooperative motion appears at about 50 K below the glass transition temperature, corresponding to the Vogel-Fulcher temperature.     

Living polymerization of 1,3-butadiene by a Ziegler-Natta type catalyst composed of iron(III) 2-ethylhexanoate, triisobutylaluminum and diethyl phosphite

Living characteristics of facilely prepared Ziegler-Natta type catalyst system consisting of iron(III) 2-ethylhexanoate, triisobutylaluminum and diethyl phosphite have been found in the polymerization of 1,3-butadiene in hexane at 40 °C. The characteristics have been well demonstrated by: a first-order kinetics with respect to monomer conversion, a narrow molecular weight distribution (M_w/M_n = 1.48-1.52) of polybutadiene in the entire range of polymerization conversion and a good linearity between M_n and the yield of polymer. Feasible post-polymerization of 1,3-butadiene and block co-polymerization of 1,3-butadiene and isoprene further support the living natures of the catalyst bestowed with. The current catalyst system is highly active (yield > 80%, 35 min), providing polybutadiene with 1,2, cis-1,4 and trans-1,4 units about 44.0%, 51.0% and 5.0%, respectively.     

Synthesis,Structures, and Catalytic Properties of Two Zinc(II) Coordination Polymers Constructed from Polycarboxylate and Bis(Benzimidazole) Ligands

Two Zn(II) coordination polymers, formulated as {[Zn(L1)_0.5(btc)_0.5(H₂O)]·H₂O} _n (1) and {[Zn(L2)(1,4-ndc)]·2H₂O} _n (2) [L1 = 1,4-bis(2-methylbenzimidazole-1-ylmethyl)benzene, L2 = 1,4-bis(2-methylbenzimidazole)butane, H₄btc = butane-1,2,3,4-tetracarboxylic acid, 1,4-H₂ndc = 1,4-naphthalenedicarboxylic acid] have been synthesized and structurally characterized by single crystal X-ray diffraction. Complex 1 features a 3D (3,4)-connected network with the topology of fsh-3,4-P2₁/c. Complex 2 is a 2D (4,4) grid with sql topology and further extends into a 3D supramolecular framework by π–π stacking interactions. In addition, the thermal stability, fluorescence, and catalytic properties of two complexes for degrading methyl orange dye in a Fenton-like process were investigated.