Structural features of disubstituted polyacetylenes with bulky substituents at double bonds

• Published in: Polymer science. Series A, Chemistry, physics Vol. 54; no. 3; pp. 187 - 194
• Main Authors: Legkov, S. A., Bondarenko, G. N., Kostina, J. V.
• Format: Journal Article
• Language: English
• Published: Dordrecht SP MAIK Nauka/Interperiodica 01-03-2012
• Subjects: Chains (polymeric); Chemistry; Chemistry and Materials Science; Infrared radiation; Mathematical models; Monomers; Polarization; Polyacetylenes; Polymer Sciences; Spectra; Structure and Properties; Vibration; Polymer Science Series; Monomer Unit; Double Bond; Internal Rotation; Mode Shape
• ISSN: 0965-545X; 1555-6107
• DOI: 10.1134/S0965545X12030054

The structural features of polyacetylenes carrying two substituents at double bonds with the general formula [-C(CH
3
)=CR-]
n
, where R = Si(CH
3
)
3
, -Ge(CH
3
)
3
, or CH(CH
3
)
2
, are studied. It is shown that the experimental IR and Raman spectra of the polymers and the theoretically calculated vibrational spectra for the model polymers consisting of three units coincide well with experimental data. All bands in the IR spectra are interpreted. The potential curves of internal rotation are calculated and constructed; high values of rotation barriers indicate a high rigidity of chains for all polymers of interest. The orthogonal arrangement of neighboring monomer units and, as a result, the absence of electron-density conjugation over the polymer chain are revealed. Charges on atoms and electron density on bonds of the monomer unit obtained from theoretical calculations indicate the presence of strong polarization of all bonds, including the -C=C- bond. This effect causes a shift in the frequencies of stretching vibrations due to double bonds in the IR spectra of polyacetylenes with Si- and Ge-containing side substituents toward the longwave region. For polyacetylene with hydrocarbon side substituents -CH(CH
3
)
2
, such polarization is absent.