Dielectric Behavior of cis-Polyisoprene in Carbon Dioxide under High Pressure

Abstract

Dielectric measurement was conducted for cis-polyisoprene (PIP) in carbon dioxide (CO 2 ) at high pressures. CO 2 is dissolved in PIP more with increasing pressure, and this dissolution is expected to affect the chain dynamics. In our experimental window, the PIP chains having type-A dipoles parallel along their backbone exhibited the dielectric dispersion reflecting their global motion. This dispersion shifted to higher frequencies with increasing CO 2 pressure. Time -CO 2 pressure superposition was found to hold well, which suggests that the global motion of the chain is accelerated by CO 2 without any heterogeneity in space and along the chain backbone. The vertical shift factor (intensity shift factor) for this superposition gave the CO 2 concentration in PIP. The plasticizing capability of CO 2 evaluated from the horizontal shift factor (frequency shift factor) was found to be a little larger than that of tetradecane in the same range of concentration. No peculiarity was found for plasticizing ability of CO 2 even in the supercritical state (at a pressure of 10 MPa).

Viscoelastic properties of solutions of polystyrene melts and carbon dioxide: Analysis of a transient shear rheology approach

“…(11) is a straight-forward generalisation of the time-temperature superpo-sition principle. Such a universal scaling behaviour was also observed in dielectric measurements [Matsumiya et al (2007[Matsumiya et al ( , 2009]. The shift factors a T,p,c are listed in Table V as a function of temperature and pressure.…”

Rheological and Dielectric Behavior of Polyisoprene under Pressurized Carbon Dioxide

“…A similar result was noted also in our previous study. 11) In contrast, at P CO2 ≥ 8 MPa exceeding the vapor pressure of CO 2 at 25 °C (= 6.8 MPa 15) ), the e 0 -e′ and e″ data become insensitive to P CO2 possibly because the dissolution of CO 2 into PI was saturated due to liquefaction of CO 2 .…”

“…The setup and the protocol of the dielectric measurements under pressurized CO 2 were basically the same as those reported in our previous studies: 11,12) The sample (PI260k) was charged between main and counter electrodes made of sintered metal (the former having a guard electrode) placed in a highpressure jacket, exposed to CO 2 having the pressure P CO2 /MPa = 0 (atmospheric ambient pressure), 2, 4, 6, 8, and 10 and fully equilibrated (as monitored through lack of the time dependent change of the dielectric data), and then subjected to the measurement at each P CO2 . All these operations were made at 25 °C, and the measurement was made in the increasing order of P CO2 .…”

“…Differing from the previous study, we utilized a CO 2 pressure controlling system, a syringe-type pump (260D, Isco) with flow panel, which was shared with the rheological setup explained later. This system enabled a little better control of the CO 2 pressure compared to the previous setup 11,12) (having direct connection to a CO 2 tank through a regulator).…”

Dielectric Analysis of Different Natural and Synthetic Polymer Types

“…Polyisoprene presents high performances regarding malleability at cold temperatures, resilience, impact resistance, abrasion and efficient heat dispersion [51]. The dielectric constant of polyisoprene at a constant temperature of 65°C varies from 2.36 to 2.28 with increasing frequency [52]. The dielectric constant of transpolyisoprene is not affected by the frequency and presented a constant value of ≈4.7 with increasing frequency from 0.1 to 10 GHz [53].…”