Structural transitions in polybutadiene examined by annihilation of positrons

Free Volume Microstructure and Its Relationship to the Chain Dynamics incis-1,4-Poly(butadiene) As Seen by Positron Annihilation Lifetime Spectroscopy

“…This development has caused a renaissance in applications of the PALS method in solving many actual problems of polymer physics such as the influence of chemical modification, , the effect of physical aging, , the effect of mechanical deformation, and the influence of mass, charge, and free valence transport. Most of the studies so far were carried out on plastics with a glass transition temperature, T g , above room temperature for reasons of easier experimentation; essentially less attention was focused on elastomers. − As for the PALS data, a puzzling aspect is the fact that the temperature coefficients of hole expansion are about 1 order of magnitude higher than the temperature coefficients of macroscopic volume expansion. ,, In addition, some polymers with a rather complicated chemical structure exhibit complicated courses in I 3 - T dependences, ascribed to the side group mobilities ,, or to the coalescence of small holes. , Finally, in a few cases practically a saturation in the lifetime τ 3 and/or of the relative intensity I 3 was observed at temperatures well above T g not only for low molecular weight substances , but also for some epoxy polymers …”

“…Most of the studies so far were carried out on plastics with a glass transition temperature, T g , above room temperature for reasons of easier experimentation; essentially less attention was focused on elastomers. [27][28][29][30] As for the PALS data, a puzzling aspect is the fact that the temperature coefficients of hole expansion are about 1 order of magnitude higher than the temperature coefficients of macroscopic volume expansion. 13,16,20 In addition, some polymers with a rather complicated chemical structure exhibit complicated courses in I 3 -T dependences, ascribed to the side group mobilities 27,31,32 or to the coalescence of small holes.…”

Photochemical and Photophysical Studies of and in Bulk Polymers

“…Similar values are obtained from positron annihilation spectroscopic studies. 78 A cross -linked, nematic, liquid crystalline elastomer ( LCE ) fi lm doped with an azo -dye, Disperse Orange I (Chart 11.3 ), has been shown to exhibit a mechanical response to nonuniform illumination. 79 The LCE consists of a poly(methylsiloxane) ( PMS ) backbone with mesogenic aromatic side -chain units.…”