Synthesis of Carbynoid Materials by Chemical Dehydrohalogenation of Halogen-Containing Polymers - Polyynes: Synthesis, Properties, and Applications - page 248

SCHEME 12.1

defects into the polymer chain, thus making complete elimination difficult
and deteriorating the structure of ultimate products.
The complete dehydrohalogenation at the second stage can be expected
to yield carbon chains of both polyyne and cumulene type, depending on the
elimination course. The latter, in turn, is governed by the structure of ori-
ginal polymer (the type and amount of intrinsic defects), by the contribution
of side reactions (substitution, oxidation, and cross-linking), and by the
length of the sp-carbon chain being formed (long polyynes were reported
to be more stable compared to cumulenes). Thermodynamic calculations
by Cataldo showed that the formation of the polyyne structure during
dehydrohalogenation is more favorable [15]. However, the contribution of
defects (side groups), the length of carbynoid moieties being formed, and the
reaction temperature, which can all affect the structure of products, were
not taken into account.
Theoretically, the chemical structure of original polymers can affect the
structure of the dehydrohalogenation products. Indeed, complete dehydro-
chlorination of poly(1,1,2-trichlorobutadiene) could be expected to result in
the formation of the polyyne form of carbyne because there seemingly is no
other way of elimination except that shown in Scheme 12.2 (B ¼ base).

SCHEME 12.2