Further EPR studies of molecular motions in polymer/plasticizer mixtures

Abstract

Molecular motions in mixtures of the side chain polymer—poly(vinyl acetate) and dibuthyl phthalate were studied as a functionof polymer concentration and temperature using the technique of paramagnetic resonance (EPR). When the small spherical probe tempol (TPL) was used, we were able to approximate the observed EPR spectrum with a simulation using a single rotational correlation time τ. The peviously developed Grest–Cohen all‐temperature model matched the Arrhenius polts. The EPR spectra from a cigar‐shaped cholestane (COL) probe could not be adequately matched by single τ simulation when the polymer was at temperatures somewhat above the glass to rubber transition temperature (Tg). Points corresponding to these temperatures were left of the Arrhenius plot and a discontinuity was observed where the gap in the data occurred. As the concentration of plasticizer was increased, we found that the discontinuity became less steep, but the τ at which the gap occurs was always ≈ 10−8. The spectra observed at the temperature region of the gap were approximately 50–50 composites of experimental spectra observed at ± K. In both the TPL and COL cases, there was evidence of the existence of multiple correlation times. Preliminary studies of other polymers, both with and without side chains, also indicated the existence of the gap when COL is used as the probe. © 1993 John Wiley & Sons, Inc.

Nitroxide Spin Probe/Label Study of Hydrogen Bonding and Probe Size Effects in a Linear Epoxy Polymer

“…Studies indicate that, in general, T50G corresponds to the temperature at which the reorientational correlation time of the spin probe is ca. 3.0 x 10~8 s. 13 The data for determination of this parameter are presented in Figure 3, and the T50G values for the label and probes in the epoxy matrix work are presented in Table 1. These values range from 20 to 150 °C.…”