Dynamic infrared linear dichroism study of poly(p-phenylene vinylene) and its precursor

Poly(p-phenylene vinylene) (PPV) has many interesting electrical properties , particularly anisotropic conductivity upon uniaxial stretching, because o f its delocalized pi-electron system. In this study we have investigated th e mid-infrared response of PPV and PPV-precursor films subjected to modulat ed uniaxial strain in order to study the degree of molecular motions and th eir time dependence during deformation. These studies have used a step-scan infrared spectrometer in conjunction with a piezo-driven irt situ Polymer Modulator(TM). The viscoelastic properties are monitored simultaneously wit h the dynamic infrared vibrational response to the applied perturbation. Th e major molecular vibrations associated with the stretching of the precurso r and of PPV have been identified and their time-dependence studied by usin g both phase-spectral and two-dimensional infrared (2D-IR) approaches. It h as also been shown that the precursor, at ambient temperatures, is elastic in nature. However, after the introduction of conjugation on the backbone v ia conversion to PPV, the material becomes more viscous; the change is evid ent at both the microscopic and macroscopic levels.