Dynamic Infrared Linear Dichroism Study of Poly(p-Phenylene Vinylene) and its Precursor

Abstract

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