Effect of pressure on the rotational mobility of spin label in polymer

Abstract

The effects of pressure on the rotational mobility of a spin label, rigidly bound to the macromolecule of divinly rubber, and of a spin probe (TEMPO radical) have been investigated. The rotational correlation time of the spin label is approximately two orders higher than that of the spin probe. The activation volumes of spin label rotation (30–40 cm 3/mol) are slightly higher than those for the spin probe (20–30 cm 3/mol). The volume of the kinetic segment (150–400 cm 3/mol) has been determined; it is concluded that the divinyl rubber kinetic segment taking part in rotation together with the label consists of 2–3 monomer units. The activation energies of label and probe rotation in rubber at constant pressure ( E p) and constant volume ( E v differ insignificantly; the ratio E v/ E p is ca 0.6–0.7. The energy necessary for the formation of a fluctuational hole differs insignificantly from the energy needed for changing the orientation of a particle when there is a fluctuation hole in the required volume. The E v values increase with rise in polymer density; therefore, with rising polymer density, the molecular interaction increases.