Poly(1,3-cyclohexadiene-1,4-diyl)

Summary Dehalogenation polycondensation of 1,4-diiodo-1,3-cyclohexadiene with zerovalent nickel complex gives a new -conjugated polymer, poly(1,3-cyclohexadiene-1,4-diyl) PCyh. A copolymer constituted of 1,3-cyclohexadiene-1,4-diyl and 1,4-cyclohexadiene-1,4-diyl is also obtained by a similar method. The black color of PCyh indicates the presence of extensive -conjugation along the polymer chain presumably due to takings-trans conformation of PCyh. PCyh is unstable and oxidized under air. IR and CP-MAS¹³C-NMR spectra of PCyh are reasonable for the structure.     

Intermediate angle scattering functions and local chain configurations of semicrystalline and amorphous polymers

Summary Molecular scattering functions at intermediate scattering vectors, of =(4/ sin/2) in the range 0.03 to 1.0Å^–1, are found to be extremely sensitive to the local configurations of polymer chains in both semicrystalline and amorphous states. Available experimental results of intermediate angle neutron scattering (IANS) from melt-crystallized polyethylene and isotactic polypropylene provide compelling evidence that adjacent re-entry is rare. The rotational isomeric state model satisfactorily accounts for IANS and chain dimensions of polycarbonate in the amorphous state.     

Wacker type and π-allyl type oxidations of propylene controlled by fuel cell system in the gas phase

Oxidation of propylene applying the (C₃H₆, Pd/H₃PO₄/Pt, O₂) fuel cell system in the gas phase produced acrolein and acrylic acid, the -allyl type oxidation products. However, addition of H₂PdCl₄ or HCl to the electrolyte reduced the -allyl oxidation, but enhanced Wacker type oxidation producing acetone. Direction to either Wacker type or -allyl type oxidation can easily be controlled electrochemically by applying the fuel cell system in the gas phase.     

Adsorption of carbon monoxide on Ni/Ti and Ni/TiO2 surfaces preparedin situ in the electron spectrometer: A combined UPS-XPS study

Adsorption of CO on a clean Ti surface is partly associative at 80 K with a 1 -4 separation of 4.2 eV, becoming dissociative at 130 K. On Ni- covered Ti surfaces, however, associative adsorption (4-1, 3.3 eV) occurs at 80 K and partial dissociation, around 200 K. TiO₂ is reduced more effectively on annealing, when it is covered with Ni. On the surfaces of Ni deposited on TiO₂, there is only dissociative adsorption, unlike on Ni/Al₂O₃ and Ni/TiO₂ (non-annealed) surfaces.Contribution No. 565 from the Solid State and Structural Chemistry Unit.     

Cryochemical Synthesis of Mn-Containing Poly(p-Xylylene)

A Mn-containing polymer was produced by solid-state photopolymerization of a cocondensated mixture of p-xylylene with Mn at 80 K. It was shown that during simultaneous deposition p-xylylene and Mn formed both - and -complexes. Irradiation of the system by UV light resulted in polymerization of p-xylylene with the destruction of the unstable -complexes, while the -bonded compounds were incorporated into the polymer chains. Complexes of Mn with benzyl-type radicals of the polymerized system were also observed. Prolonged storage of the polymerized material at ambient temperature under vacuum led to the gradual decomposition of the organomanganese compounds and complexes.     

A solid-state electrochromic device based on complementary polypyrrole/polythiophene derivatives and an elastomeric electrolyte

A device was assembled using optically transparent glass electrodes and combining two complementary electrochromic polymeric materials, poly(4,4-dipentoxy-2,2-bithiophene) and poly(N,N-dimethyl-2,2-bipyrrole). As electrolyte we used an ionically conductive polymer; poly(epichlorohydrin-co-ethylene oxide) containing a lithium salt. The optical contrast in the visible/near infrared region, stability to repeated redox cycles and electrochromic efficiency are reported and discussed.     

Hreels characterization of the room temperature phase of propene adsorbed on ruthenium (001)

Room temperature adsorption of propene on ruthenium (001) was studied by HREELS and UPS. Adsorption was mainly dissociative, with cleavage of both C-H and C-C bonds, and resulted in a mixture of surface species: naked carbon atoms, CH fragments, metal carbynes, ethylidyne, di- adsorbed alkene, and -adsorbed alkene in order of their relative abundance.     

Synthesis,electroconductivity and third-order nonlinear optical property of poly(2-isopropoxy-5-methoxy-1,4-phenylenevinylene)

Summary Asymmetrically disubstituted poly(2-isopropoxy-5-methoxy-1,4-phenylene-vinylene), PIMPV, was prepared in thin films via organic-soluble precursor polymer method. These polymer films could be easily stretched up to 7 times, and the drawn films of the PIMPV could be doped with FeCl₃ and I₂ to give conductivities of 26.9 and 11.3 Scm^-1, respectively. The third-order nonlinear optical susceptibility of the polymer was determined using third harmonic generation(THG) method at 1907 nm, fundamental wavelength. Measured ⁽³⁰⁾ (-3: , , ) value was 3.7x10^-12 esu.     

Preparation of Linear π-Conjugated Coordination Polymers Having Ruthenium(II) Complex in the Main Chain

Soluble -conjugated coordination polymers having a ruthenium(II) complex in the main chain were prepared from a soluble metal complex monomer and a bridging ligand via coordination. Refluxing of an ethanol-water suspension containing (4,4-dinonyl-2,2-bipyridyl)Ru(III) with 2,3-bis(2-pyridyl)pyrazine gave the coordination polymer. The resulting polymer was soluble in common organic solvents. The structure was confirmed by uv/vis spectra and gpc analysis.     

Electron Transfer in Ferrocene-containing π-conjugated Polymers

We describe here our recent research on -conjutgated organometallic polymers containing ferrocenyl groups. Internuclear electronic interactions through the -conjugated spacer display unique redox and optical properties. The dependence of the redox properties on the number of ferrocene moieties in oligo(1,1-ferrocenylene)s were analyzed by the neighboring-site interaction model. The electronic structure in the mixed-valence states of biferrocene and terferrocene were estimated using the infrared (IR) spectra. Intervalence-transfer (IT) bands in the mixed-valence states of oligo(1,1-ferrocenylene)s were rationalized by taking into account the change in neighboring-site interaction by photo-electron transfer. Near-IR photoconductivity was found for the charge transfer complex of oligo- and poly-(1,1-ferrocenylene)s with tetracycanoethylene (TCNE). Redox and optical properties of azo-bridged ferrocene oligomers and a polymer was also analyazed based on the neighboring-site interaction model. Metallacyclization reaction of para-bis(ferrocenylethynyl)benzene with CpCo(PPh₃)₂ affforded a ferrocene-containing cyclobutadienecobalt polymer, of which redox property indicates strong intra-unit and weak inter-unit interactions.     

Characterization of some organic poly(aminiumphosphate)s

Summary Metachromatic reactions of MB and AO are studied with poly(aminium phosphate)s. The main band() at 665 m and 492 m for MB and AO are shifted to 580 m and 455 m respectively (-bands). The metachromatic values at different concentrations of poly(aminium phosphate)s are also reported. The dye association for MB with these polymer derivatives is investigated conductometrically as well. It is observed that MB can be at the most bind with the phosphate residue of polymer upto 11 molar ratio. The polymeric nature was further established by paper chromatographic technique in Terry's, Ebel's & Pfrengle's solvents.     

Ultraviolet study of the solvent induced coil to helix transition of poly(α-L-glutamic acid)

Summary The coil to helix transition of polypeptides can be induced by lowering the pH in pure aqueous solutions, or by adding an organic solvent to an aqueous solution of the polypeptide (starting pH higher than 7.0 for poly--L-glutamic acid) (MORCELLET and LOUCHEUX 1978a). It has been shown since many years that the pH induced transition of poly (-L-glutamic acid) (PGA) may be followed by U.V. spectroscopy since the X absorption band of the peptide chromophore near 190 nm exhibits strong hypochromism when the polypeptide is under the helical conformation (IMAHORI and TANAKA 1959). Similar results have been also obtained about an other extensively studied polypeptide, poly-L-lysine (ROSENHECK and DOTY 1961, CHOU and SCHERAGA 1971). The present paper shows that the solvent induced transition of PGA may also be monitored by U.V. spectroscopy.Equipe de recherches associée au CNRSn 827     

Opposing Effects of Host Monoterpenes on Responses by Two Sympatric Species of Bark Beetles to Their Aggregation Pheromones

The effects of host tree monoterpenes on primary and secondary attraction of the bark beetles, Ips pini and Ips grandicollis, and their associated phloeophagous insects were investigated. Monoterpenes alone were not attractive to I. pini. However, monoterpenes mediated the attraction of I. pini to its aggregation pheromones. With the exception of 3–carene, the effect of monoterpenes on I. pini's response to its pheromone, ipsdienol plus lanierone, was inhibitory. In contrast, (–)--pinene both attracted I. grandicollis and enhanced the attraction of I. grandicollis to its pheromone, ipsenol. No monoterpene inhibited the response of I. grandicollis to its pheromone. The inhibitory effect of host monoterpenes on I. pini response to its aggregation pheromone differs from previous work, in which monoterpenes either synergized responses or had no effect. In addition to possible geographic differences, the concentrations used in our study simulated trees that had begun to respond to attack, whereas previous studies deployed lower concentrations, which simulated constitutive phloem from unattacked trees. These results support the view that trees that undergo induced responses to bark beetles sometimes inhibit attraction of additional beetles, despite the beetles' production of aggregation pheromones. Neither species displayed cross-attraction to the pheromone of the other. The red turpentine beetle, Dendroctonus valens, showed weak and consistent attraction to (+)--pinene and in some cases to (–)--pinene. Attraction to (–)--pinene was usually enhanced by Ips spp. pheromones. The absence of strong attraction to (+)--pinene and partial attraction to (–)--pinene suggest that the effects of different stereoisomers of -pinene on D. valens vary throughout its geographical range. Hylastes porculus was also attracted to some monoterpenes, particularly (–)--pinene. An additional 10 species of phloeophagous insects were caught in response to monoterpenes and/or pheromones, including the pine root weevils, Hylobius pales and Pachylobius picivorus, and the longhorned beetle, Monochamus carolinensis.     

Theoretical aspects of bonding in silicon compounds

Ab initio-calculated bond dissociation energies of Si=Si and C=C are discussed by means of atomic ionization energies and p-p() AO overlap. At the same time ring strain energies of C- as well as Si-rings are estimated by homodesmic reactions where, according to Baeyer, the two-membered rings C=C and Si=Si are chosen to be the first members of the respective series. Thus, a better understanding of the double bonds can be gained. In addition, the exceptional structural and spectroscopic behavior of the five-membered Si-ring is discussed. Finally, the strikingly different results obtained in computational studies of the initial step for polymerization of the systems O=C=O and O=Si=O are discussed.     

Poly(pyridine-2,5-diyl)–CuCl2 catalyst for synthesis of dimethyl carbonate by oxidative carbonylation of methanol: catalytic activity and corrosion influence

A -conjugated polymer, poly(pyridine-2,5-diyl) (PPy) was investigated as a support for CuCl₂ in the synthesis of dimethyl carbonate by oxidative carbonylation of methanol. The PPy–CuCl₂ adduct had high catalytic activity which was comparable to that of the homogeneous CuCl₂ catalyst. The adduct caused corrosion of stainless-steel vessels only to minor extent, compared with the homogeneous CuCl₂ catalyst. This PPy–CuCl₂ catalyst was easily recycled by filtration and showed a similar catalytic activity in the third time use. The presence of the -conjugated system in PPy, through which electrons can move, may bring about the high catalytic activity for the oxidative carbonylation of methanol, which involves Cu(II)/Cu(I) redox processes.     

Inhibition of phosphoric acid corrosion of zinc by organic onium compounds and their adsorption characteristics

The inhibiting properties of some organic phosphonium and ammonium compounds were studied with respect to the corrosion of zinc in 1 M H3PO4 solution. It was found that onium compounds which have -electron system(s) are adsorbed following Frumkin's adsorption isotherm and provide better inhibition efficiency than those containing no -electron system. The adsorption of the latter compounds was found to obey Langmuir's isotherm. Both potentiostatic and electrochemical impedance techniques proved that the studied onium compounds act as primary interface inhibitors without changing the mechanism of either hydrogen evolution reaction or zinc dissolution.     

ΔCp, Δα and related quantities for epoxy-aromatic amine networks

Summary The parameters of glass transition in several epoxyamine polymer networks were obtained. The changes C_p (T_g) and (T_g) were proved to be correlated with the concentration of crosslinks in these systems. The difference in glass transition parameters for linear and densely crosslinked polymers was analysed in terms of Simha-Boyer (T_g) and Boyer (C_p·T_g) rules and Eyring's hole theory.     

New ring-opening polymerization via a π-allylpalladium complex

Summary A binary system of a palladium complex as catalyst and zinc alkoxide as initiator conducted a novel ring-opening polymerization of cyclic carbonate, i. e., 5,5-dimethyl-4-ethenyl-1,3-dioxan-2-one. The polymerization proceeded along with releasing carbon dioxide to produce the corresponding polyether. The -allylpalladium complex generated from the monomer with the catalyst is the key intermediate for this new polymerization. The propagating end is zinc alkoxide, which nucleophilically attacks the monomer activated as the -allylpalladium complex in the propagation.     

Synthesis and characterization of poly(11-(4′-cyano-trans-4-stilbenyloxy)undecanyl vinyl ether)

Summary Polymers based on 11-(4-cyano-trans-4-stilbenyloxy)undecanyl vinyl ether have been synthesized by living cationic polymerization, photo-initiated cationic polymerization using onium salts and thermal initiated cationic polymerization using onium salts. The polymers have been characterized by size exclusion chromatography, nuclear magnetic resonance spectroscopy, differential scanning calorimetry and polarized light microscopy. Living cationic polymerization resulted in a polymer of low molecular mass M_n3 600, with a uniformity index (D) of 1.2 displaying a focal conic texture indicative of smectic A (s_A) phase with preserved cyanogroup and trans-configuration. Photo-initiation using 2,4,6-trimethylbenzoylethoxyphenylphosphine oxide and diphenyliodonium hexafluorophosphate resulted in an insoluble polymer exhibiting only vague liquid crystalline textures. Initiation with phenothiazine and phenacyltetramethylenesulfonium hexafluoroantimonate also yielded a partly insoluble polymer with a disturbed s_A phase. It is suggested that the monomer and polymer are sensitive towards radicals leading to cross-linking and branching. The thermal initiation on systems with -methylbenzyltetramethylenesulfonium hexafluorophosphate and p-methoxybenzyltetramethylenesulfonium hexafluorophosphate resulted in completely soluble mesomorphic polymers of M_n13 000, D=1.7 and M_n26 000, D=2.8 respectively, in both cases with a preserved cyanogroup and a transconfiguration. Polarized light microscopy revealed a distinct focal conic structure indicative of s_A in both cases.     

Stress and recovery maxima in LDPE melt elongation

Summary By means of a new tensile rheometer for polymer melts, stress-strain curves () and the elastic recovery _R() of a low density polyethylene melt were measured up to total strains =7, i.e. stretch =1097, at 150°C and two strain rates, =0.03 and 0.1 s^–1. Tensile tests up to very high strains e give relevant results only if the test performance is characterized by quality parameters which are defined and given in this paper. The test results show a maximum in a as well as in _R at about =5.5. Hence, in the range of investigated, a rheologically steady-state of flow does not exist.