ABSTRACT:The infrared spectra of poly(acetylene), poly(acetyiene-d2), copoly(acetylene+acetylene-d2), and copoly(acetylene tacetylene-d1 +acetylene-d2) prepared by the Ti(OC4H9)4-Al(C2Hs)3 system over a wide temperature range (ca. -100 to 180°C) are reported. A tentative assignment of the observed spectra is made on the basis of model structures in which infinite planar chains of all trans, all trans-cisoid, and all cistransoid configurations are assumed. The spectral data are best interpreted on the basis of an all cis-transoid (or an all trans-cisoid) structure for the polymers prepared at temperatures lower than -78°C, and an all trans structure for the polymers prepared at temperatures higher than 150°C.Simplified calculations of the C-H and C-D out-of-plane deformation frequencies are made for various model chains. It has been concluded from a comparison of the observed and calculated frequencies that the cis-opening of the triple bond occurs in a polymerization reaction with the Ti(OC4H9)4-Al(CzHs)3 catalyst system at low temperatures.KEY WORDS Infrared SpectrajPoly(acetylene)/Deuterated Acetylene/ Ziegler Catalyst/Configuration/cis-Opening/Factor Group Analysis/ Normal Vibration/ Structure and properties of poly( acetylene) prepared with Ziegler-Natta catalysts have been investigated by several groups. Natta, et a!./ presented evidence from chemical properties and X-ray diffraction data, indicating that the poly-(acetylene) obtained had linear chains of conjugated double bonds of trans configuration along the chains. poly(acetylene) containing a 60-70% cis content obtained by a catalyst system of thermally decomposed iron dimethylglyoximate-2-pyridine and triethylaluminum at 25°C or below.

In order to elucidate the structural details of doped polyacetylene (a highly conducting organic polymer), the optical absorption, Raman, and infrared spectra of not only trans-(CH)x doped with iodine, AsF" and SO, but also f3 -carotene doped with iodine and SO, were studied. The infrared spectra of two kinds of isotopically substituted polyacetylenes (CD), and C'CH), doped with iodine were also observed.Analysis of the experimental results shows that upon doping each of the four vibrational branches (v I-V.) in the 1600-900 cm-I region of a polyene chain splits into two groups, namely, the higher frequency group and the lower frequency one. The former group consists of the "gerade" vibrations of polyene parts which are not directly attacked by dopants but are perturbed along the chain, whereas the latter is made up of the "ungerade" vibrations of the positively charged polyene part with the doped site at its center. The Raman bands in the higher-frequency group of VI (mainly the C=C stretching mode) observed with various laser lines give definite information on the segments of conjugated trans double bonds existing in doped polyacetylene. The Raman spectra are also useful for clarifying the structures of dopants. In the infrared spectra of doped trans-(CD)x and C'CH), the bands appearing on doping all showed respective isotope shifts which confirmed the view that these bands are of vibrational origin. In many respects doped f3 -carotene proved to be a useful model of doped trans -polyacetylene.

A series of dialkyl(dipyridy1)nickel complexes R,Ni(dipy) (1, R = CH3, CzHs, n-CSH5, or i-CIHO) was prepared. The thermal stability of 1 decreases in the order CH3 > C2H5 > C3H7 > C4H9. Thermal decomposition of 1 is first order with respect to 1, and the activation energy for pyrolysis of (CzH&Ni(dipy) is 68 kcal/mol. Reactions of 1 with olefins (tetracyanoethylene, maleic anhydride, acrylamide, acrylonitrile, methacrylonitrile, acrolein, methyl vinyl ketone, methyl acrylate, methyl methacrylate, vinyl chloride, vinyl acetate, 2-vinylpyridine, styrene, isobutyl vinyl ether, ethylene, norbornene, and cyclooctadiene) at room temperature led in most cases to cleavage of the R-Ni bond and to formation of olefin-coordinated complexes of the type Ni(dipy)(olefin), (3, n = 1 or 2). The R-Ni bonds are activated through coordination of the olefins to 1; with acrylonitrile and acrolein the complexes R,Ni(dipy)(olefin) (2) were isolated as unstable intermediates. From infrared and electronic spectroscopy, the coordinated olefins in 2 and 3 appear to be T bonded. Based on a kinetic study of the reactions of 1 with olefins at room temperature a mechanism involving the formation of 2 as an intermediate is proposed. Olefins with electronegative substituents form stronger T complexes with 1 and activate the Ni-R bonds more strongly than those with less electronegative substituents. The observation of charge-transfer bands in the complexes allows estimation of the energy levels of the highest occupied d orbitals and a study of the effect of solvent and olefin coordination to the metal. A mechanism for the activation of Ni-R bonds by interaction of 1 with olefins is proposed.he coordination of olefins with alkyl-transition (8) A. Yamamoto, T. Shimizu, and S . Ikeda, P0lj.m. J . , 1, 171 (1970); Makromol. Chem., 136, 297 (1970).(9) Previously we reported that (CnH&Ni(dipy) also initiates the polymerization of acrylonitrile,e but we confirmed later that the initiation requires the presence of a trace of oxygen, whereas this is not the case for ethyliron and -cobalt complexes.

Thermal cis‐trans isomerization and decomposition of polyacetylene film prepared with a Ti(OC4H9)4–Al(C2H5)3 (Al/Ti = 4) system were investigated under inert gas or in vacuum by means of thermal analysis and infrared spectroscopy. Thermograms of differential thermal analysis of cis‐polyacetylene revealed the existence of two exothermic peaks at 145 and 325°C and one endothermic peak at 420°C which were assigned to cis‐trans isomerization, hydrogen migration accompanied with crosslinking reaction, and thermal decomposition, respectively. The isomerization was followed by infrared spectroscopy over the temperature range 75–115°C. The reaction did not obey simple kinetics. The apparent activation energy for the cis‐trans isomerization was 17.0 kcal/mole for the polymer containing 88% cis configuration and increased with increasing trans content up to 38.8 kcal/mole for 80% trans content.

The electrical conductivity of crystalline polyacetylene films having various cis-trans compositions was measured. The resistivity and the energy gap of a 92,5% trans polymer were 1,Ol .l@R.cm and 0,56 eV, respectively, whereas the values of a 20,0% trans polymer were 2,35.10* R . cm and 0,93 eV, respectively. These differences are discussed in terms of the effective conjugation length estimated from visible spectra and ESR measurements, and the spacing between molecular planes obtained by x-ray diffraction measurements.

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A direct method of simultaneously polymerizing and forming acetylene monomer to produce uniformly thin films of polyacetylene was investigated in terms of catalyst system, catalyst concentration, and polymerization temperature. The best catalyst was a Ti(OC4H9)4–Al(C2H5)3 system (Al/Ti = 3–4) and the critical concentration was 3 mmole/l. of Ti(OC4H9)4. Below the critical concentration, only a solid or a powder was obtained. The configuration of the polymers obtained depends strongly upon the polymerization temperature. Thus an all‐cis polymer was obtained at temperatures lower than −78°C, whereas an all‐trans polymer resulted at temperatures higher than 150°C. Observations either in an electron microscope by direct transmission or in a scanning electron microscope showed that the film is composed of an accumulation of fibrils about 200–300 Å in width and of indefinite length.

SynopsisPolymerization of propylene carbonate was carried out at 12O-18O0C mainly with the use of diethylzinc catalyst. The polymer was a pale-yellow, viscous material of relatively low molecular weight (IOOO-iOOO). From the spectroscopic analysis of the polymer and its hydrolyzed product, the polymer was determined to have the structure CH, CH, CH3 CH, CH,where Y = 0.50, y = 0.25, and z = 0.25. This strongly suggested that the polymerization of propylene carbonate proceeded via 2,7-dimethyl-1,4,6,9-tetraoxaspiro[4,4]nonane (DTN) as an intermediate compound. Hence, DTN was synthesized and polymerized with the use of diethylzinc catalyst. The structure of the polymer thus prepared coincided exactly with that of the polymer from propylene carbonate. From these, a plausible mechanism of the polymerization was developed.