Broadband Electric Spectroscopy at High CO2 Pressure: Dipole Moment of CO2 and Relaxation Phenomena of the CO2-Poly(vinyl chloride) System

Broadband electric spectroscopy (BES) is a technique that shows promise in studying the interactions of dense or supercritical gases with polymers, particularly with respect to chain mobility. Polymers that are treated with dense gases show a reduction in the viscosity, glass transition, and melting temperature. A high pressure cell for BES has been constructed that can be used from ambient temperature and pressure to 353 K and 15MPa and over a frequency range from 20 Hz to 1MHz. In the past, the dielectric constant of CO2 was determined by measurements at only one or two frequency values. New instrumentation and technology allow this experiment to be expanded to cover a wider frequency range. BES measurements of CO2 do not show any relaxation peaks in the permittivity from 20Hz to 1MHz and 1 to 6MPa. By these measurements, theCO2 dielectric constant was evaluated between 0.1 and 6MPa. Cell testingwith poly(vinyl chloride) (PVC) at 323 K and CO2 pressures from 0.1 to 13 MPa indicate an increase in the chain segmental motion at high pressures resulting from a reduction in the glass transition temperature of the PVC-CO2 system due to plasticization by CO2