An FTIR spectroscopic study was carried out for rare-earth polyacetylenesa) (PA) containing both Z ("cis") and E geometric isomers. Spectral assignments were made by the study of PA samples with different Z/E ratios and by referring to the known assignment of the IR spectrum of PA obtained with Ti(OC&), . Al(%H&. The conjugation effect of Z or E -CH=CH-sequences and their length distribution in PA are investigated by spectral subtraction and peak separation. It is shown that the frequency of v(CH) (out-of-plane deformation) is located in the regions 741 to 747 cm-' and 940 to 1014 cm-* for Z-and E-PA, respectively, depending on the conjugation length. At the beginning of thermal isomerization of Z-PA, long Z sequences are interrupted quite frequently; this causes a shift of v(CH) towards higher frequencies. In high E-PA obtained by thermal isomerization of Z-PA, uninterrupted long E sequences persist. This demonstrates that a crosslinking reaction between PA chains is not conspicuous during the thermal isomerization process.
Thermal isomerization kinetics of high 2 (> 90Vo) rare-earth polyacetylene b, was studied by Fourier transform infrared spectrophotometry in the temperature range of 354 to 443 K. The isomerization kinetics do not follow any simple kinetic reaction order; the apparent activation energy was determined to be 48,l kJ .mol-'. The 2 to E isomerization in polyacetylene is discussed in terms of a diradical two-step mechanism. a) Part I : cf. 15). b, IUPAC name: poly(viny1ene).
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