Synthesis of Carbynoid Materials by Chemical Dehydrohalogenation of Halogen-Containing Polymers - Polyynes: Synthesis, Properties, and Applications - page 257

halide was removed from the polymer within 12 h of reaction. Subsequently,
the reaction slows down further, and even within 4 days the conversion still
did not exceed 60%. When the original polymer powder was refluxed in a
10% t-BuOK solution in THF at 65 C for 4 h, the degree of dehydroha-
logenation was found to be 68%. However, higher temperatures are known
to cause extended cross-linking and the formation of graphite-like structures
during the dehydrohalogenation process [7,8]. The spectrum of the final
product exhibits conspicuous features at 27.5 (strong, sharp), 45.9
(shoulder), 81.5 (weak), 111.8 (medium), 121.4 (shoulder), 149.4 (weak),
178.3 (weak), and 188.7 ppm (weak, shoulder). While the peaks at 27.5, 45.9,
111.8, 121.4, and 178.3 ppm are associated with the starting material, the
other features appear in the spectra due to chemical transformations
occurring in the polymer. The feature at 81.5 ppm is attributable to isolated
triple C C-bonds inasmuch as conjugated polyynes are known to resonate

in a 60-70 ppm region [18]. The peak at 149.4 ppm can be assigned to
fluoromethine ¼ CF-carbons in conjugated double C ¼ C-bonds. Finally, the

shoulder at 188.7 ppm is attributable to carbonyl C O groups formed by

oxidation of multiple bonds in the reaction products during synthesis or
work-up procedures.
The 13 C NMR results along with the IR spectroscopic data have shown
that chemical dehydrohalogenation of poly(ethylene-alt-chlorotrifluor-
oethylene), by treating with potassium tert-butoxide in THF, mainly yields
halogen-substituted polyenyne structures containing randomly distributed
isolated triple C

¼

C-bonds. Based on the predominant structure of the
original polymer, the polyene fragments can be described as head-to-head
polyfluorovinylenes (Scheme 12.8).

SCHEME 12.8

Recently, Cataldo reported on 13 C NMR spectra of the dehydrochlor-
ination products of chlorinated docosane, which were measured in solution
[16]. The spectra show four broad but clear signals at 40, 45-70 (centered at
60), 85-95, and 125-135 ppm attributable to saturated (sp 3 ) carbon atoms
bearing residual chlorine, polyyne sequences, isolated or carbonyl-conju-
gated triple bonds, and polyene structures, respectively.

12.5 CONCLUSIONS

Modern spectroscopic techniques have allowed one to conclude that seem-
ingly simple and straightforward reaction of chemical dehydrohalogenation