Synthesis, characterization and theoretical interpretation of vibrational spectra of poly(2-methylbut-2-enyl thiophene-3-carboxylate)

Electroactive thiophene substituted polyacetylene derivative, namely poly(2-methylbut-2-enyl thiophene-3-carboxylate) (PMT) was synthesized. First, novel acetylene monomer was synthesized by the reaction of 3-thiophenecarboxylic acid with propargyl bromide and then polymerized with a Rh catalyst to give the corresponding polymer. FTIR and FT-Raman spectra were recorded experimentally and used for complete normal mode analysis using Wilson's GF matrix method and Phonon dispersion of poly(2-methylbut-2-enyl thiophene-3-carboxylate). The simple non-redundant set of internal coordinates and a simplified Urey-Bradley force-field approximation was employed in normal coordinate analysis and to calculate the potential energy distribution (PED) for each fundamental vibration. The PED contribution corresponding to each of the observed frequencies shows the reliability and accuracy of the spectral analysis. Apart from detailed assignments of modes, various characteristic features of dispersion curves have also been explained as arising due to internal symmetry in energy momentum space. Predicted values of intramolecular contribution to the heat capacity of this polymer calculated by density-of-states are also being reported.