ABSTRACT

We report on the dynamical behavior of spin probe 2,2,6,6 – tetramethyl – 1 - piperidinyloxy (TEMPO) in amorphous van der Waals-type glass-forming polymer poly (isobutylene) (PIB) as measured over a wide temperature range by electron spin resonance spectroscopy (ESR). To reveal the relative influence of physical factors controlling the spin probe dynamics, the reorientation properties of TEMPO were related to the free volume data on PIB as obtained from positron annihilation lifetime spectroscopy (PALS) as well as to the relaxation results on PIB from nuclear magnetic resonance (NMR) and broadband dielectric spectroscopy (BDS). The characteristic ESR temperatures ( ,  and ) determined from the spectral parameter of mobility, , and those ( ,  and ) from the rotational correlation time, , as a function of temperature, were found to be related to the characteristic PALS temperatures , and  from phenomenological analyses of the temperature dependences of the mean o-Ps lifetime, , and the width of the o-Ps lifetime distribution, . Further, the close relationships between the spin probe size  and the free volume hole size distributions  at = and  point towards the role of free volume in the slow to rapid regime transition or in the crossover within the rapid regime, respectively. Moreover, closeness of  and  with  as well as of  with  indicate the common origin of the underlying processes. The origin of these ESR and PALS coincidences can be traced out towards the secondary  and  processes as detected by nuclear magnetic resonance or broadband dielectric spectroscopy, respectively.