Molecular probe dynamics and free volume in glass-formers: 1,2- and 1,4-poly(butadiene)s

We report on the mutual relationships between reorientation and free volume in two poly(butadiene)s as seen by TEMPO and ortho-positronium (o-Ps) using ESR or PALS, respectively. The slow to fast transition of TEMPO in cis–trans-1,4-PBD and 1,2-PBD occurs at the similar characteristic ESR temperature T50G with T50G/TgDSC = 1.22 for the former in contrast to T50G/Tg = 0.85 for the latter. In spite of the T50G < Tg relation an empirical rule τ3 (T50G) = 2.17 ± 0.15 ns is confirmed suggesting that the main transition of TEMPO in 1,2-PBD occurs at the same free volume fluctuation independently of the physical state of the host matrix.