Computational chemistry study of polymethylsiloxane structure and vibrational spectra

The models describing the polymethylsiloxane xerogel were constructed. The size varies from 1 to 25 silicon atoms. Their structure, IR and INS (inelastic neutron scattering) spectra where calculated using AM1 and PM3 methods. The calculated IR spectra shows characteristic splitting in the 1000 cm(-1) -1200 cm(-1) area. The INS spectra, being much more sensitive to the conformation, varies much more, depending on the model. The models, which calculated spectra fit best the experimental data, are considered to be realistic parts of the polymethylsiloxane xerogel. The causes of success and failure of spectra fitness are discussed. It is concluded that polymethylsiloxane xerogel should be considered as a loose net with 3-5 silicon atoms between nodes.