Electrochemical Synthesis of Carbyne-Like Materials and Other Nanocarbons - Polyynes: Synthesis, Properties, and Applications - page 63

The electrochemical carbonization of PTFE is anisotropic, propagating
rapidly along the oriented macromolecule chains [12,54]. Although the aim
of early studies [12,13,50-54] was just surface modification of PTFE for
improving of its adhesion, the authors have intuitively suggested the forma-
tion of polyyne (cf. Eq. 4.18) [52]. This prediction was later confirmed by IR
spectroscopy [56,60,61]. The reactivity of ex-PTFE carbon was recently used
for its subsequent functionalization with diazonium salts [62] and metalli-
zation [63].
Besides direct electroreduction of PTFE on metal cathode, the indirect
dehalogenation was carried out by electrochemically generated reactants.
A classical reaction employs naphthalene radical cation, which is generated
electrochemically in a solution of naphthalene in dimethylformamide

þ
NBu 4 BF 4 or NBu 4 ClO 4 [50,56] (Eq. 4.20). The radicals react with PTFE
while the naphthalene is regenerated (4.20a) and the reaction propagates in
a catalytic loop:

e ! C 10 H 8

C 10 H 8 þ ð 4 : 20 Þ

C 10 H 8 þ F þ 1 = 4n ð CF 2 CF 2 Þ n ! 1 = 4n ð C C Þ n þ C 10 H 8 ð 4 : 20a Þ

Amatore et al. [64] studied similar reactions mediated by phthalonitrile,
4-cyanopyridine, pyridazine, 4-phenylpyridine and benzonitrile. They aimed
at detailed kinetic analysis, while the nucleophilic radical anion was gener-
ated at a gold-band ultramicroelectrode [64]. An alternative approach,
employing inorganic reductant, instead of organic radical cation, was
introduced by Yasuda et al. [65-71]. The electrochemical carbonization of
PTFE proceeded in tetrahydrofuran electrolyte solution into which a sacri-
ficial Mg anode dissolved galvanically. It was suggested that the active
reactant for carbonization is the magnesium radical cation, Mg þ , though
this species is not well defined [70]:

Mg þ þ F þ Mg 2 þ 1 = 4n ð CF 2 CF 2 Þ ! 1 = 4n ð C C Þ þ ð 4 : 21 Þ

Poly(chlorotrifluoroethylene) (PCTFE) is also smoothly carbonizable by
electrolysis in aprotic media [72-75]. The carbonization is slower for crys-
talline PCTFE as compared to amorphous polymer [76], and for a polymer
pretreated with g -photons [73]. The structure of carbonized PCTFE was
investigated in less detail compared to that of ex-PTFE carbons.
The partially halogenated hydrocarbons, such as poly(vinylidene fluo-
ride) (PVDF) and polyvinylchloride (PVC) are not carbonizable by direct
reductive dehalogenation [59]. Nevertheless, PVDF carbonizes indirectly by