Thermal isomerization of cis-poly(phenylacetylene). Scission of polymer main-chain and formation of 1,3,5-triphenylbenzene as a pyrolysis product

Cis-trans isomerization and13C-NMR chemical shift of polyphenylacetylene

“…The 80°-deflected transpoly(phenylacetylene) (deflected trans-PPA) was prepared in the following way. 8,9,17 The powder sample of cis-PPA was sealed under nitrogen atmosphere in a glass tube and annealed in an oil bath at 180°C for 1 h, because the exotherm of the cis-trans isomerization began at 150°C and was brought to an end at 180°C. After cooling, the sample was dissolved in chloroform and then poured into n-hexane to remove the pyrolysis byproducts of triphenylbenzene and low molecules, etc.…”

“…In the MO calculations, we take account of not only planar zigzag configurations such as cis-transoidal, trans-cisoidal, and transtransoidal forms, but also the same deflected configurations as the TGЈTGЈ-type for the trans chain in poly(vinylidene fluoride) reported by Hasegawa et al 19 The cis-cisoidal forms of the chain was not used in the calculation, because the steric hindrance of phenyl groups in PPA chain did not allow the considerable helical structure of the chain. 6,8,17 Figure 1 shows the backbone geometry of the same deflected trans chain conformation projected on a perpendicular plane and a perpendicular axis to its axis. The deflected angle of corresponds to the dihedral angle between two double bonds in the main chain.…”

“…The two kinds of 13 C peaks in the spectrum of deflected trans-PPA are attributed from the phenyl group and the main chain, because pyrolysis byproducts of triphenylbenzene and low molecules were removed completely. 6,17 Comparing the respective peaks of the deflected trans-PPA with those of the cis-PPA, peak 1 shifts downfield by 0.24 ppm, but peak 2 becomes broader and shifts upfield by 3.07 ppm. Table I lists the chemical shift values of the two peaks and the respective chemical shift variations, ⌬␦s, for cis-and deflected trans-PPAs.…”

Molecular weight and configurational stability of poly[(fluorophenyl)acetylene]s prepared with metathesis and insertion catalysts

“…Because this process leads to the decrease in polymer solubility no data are available on the eventual changes of MW of isomerized polymers. The cis ‐to‐ trans isomerization of bulk high‐ cis polyarylacetylenes has also been induced by enhanced temperature70, 73 or intensive light irradiation 74. The temperature‐induced isomerization was accompanied by decrease in polymer MW and significant extrusion of triarylbenzenes 73, 75.…”

SEC/DAD and1H NMR Study of Molecular Weight and Configurational Stability of Poly(2,4-difluorophenylacetylene) and Polyphenylacetylene Prepared with Rh Catalyst

“…The subject of particular interest in this field has been the pressureinduced cis-to-trans isomerization of these polymers in the solid state. [69][70][71][72][73][74] This phenomenon is manifested by (i) red shift in the UV-Vis spectra due to the increase in the effective conjugation length and (ii) a significant increase in the concentration of mobile unpaired electrons (solitons) on the polymer chains. [69] Since this process usually leads to the decrease in polymer solubility no reliable data is available on the eventual changes in MW accompanying cis-to-trans isomerization.…”