Intramolecular
acid-catalyzed cyclization was suggested for the
first time for a polyaniline derivative, namely, poly[2-(2-chloro-1-methylbut-2-en-1-yl)aniline]
(PClPA), to give hitherto unknown poly(2-ethyl-3-methylindole)
(2E3MPIn) in a high yield (81%). This is the first example
of synthesizing a polymer of the indole series with 1,5-addition of
monomeric units that are incorporated into the polymer structure.
The physicochemical properties of the new polymer were studied. Its
structure was confirmed by spectral methods and quantum-chemical calculations.
The 2E3MPIn polymer showed good thermal stability compared
to the starting PClPA polymer. A study of the photoluminescence
of polymers showed that the emission spectrum of 2E3MPIn demonstrated a bathochromic shift (16 nm) and a considerable increase
in the luminescence intensity in comparison to PClPA.
The 2E3MPIn sample was found to possess photoconductivity.
Irradiation of the polymer film increases the electrical conductivity
by a factor of 2. The electrochemical properties obtained from the
UV–vis spectrum and cyclic voltammograms suggest that 2E3MPIn has good electroactivity. A sample of 2E3MIn demonstrates a fine porous structure resembling a “sponge”.
In addition, the PClPA and 2E3MPIn samples
synthesized were used as sensitive materials in resistive moisture
sensors. The 2E3MPIn polymer demonstrated a higher response
than PClPA to changes in the environment humidity. The
observed changes in the physicochemical properties of 2E3MPIn compared to PClPA confirm that the polyheterocyclization
reaction occurs successfully and can be considered as an efficient
way for synthesizing new functional polymers of the indole series.