Compton Scattering from PTFE: Probing Electron-Charge Redistributionin Polymer Phase Transitions

Compton profiles of polytetrafluoroethylene (PTFE) at room temperature and at higher temperatures up to and above the melting point are reported. For the first time, one has experimental evidence that thermally induced conformational excitations of the polymer chains are accompanied by a charge transfer, related to the $\sigma$- and $\pi$-molecular orbitals (MO) of the C-F bond. It is argued that localization of the $\pi$-MO related to the fluorine atom facilitates the translational movements of the chains, while the weakening of the C-F bond and the transition from a crystalline to an amorphous phase are associated with delocalization of $\sigma$-MOs.