title: Dynamic crossovers and activated regimes in a narrow distribution poly(n-butyl acrylate): an ESR study.
abstract: The rotational dynamics of the spin probe cholestane dissolved in a narrow distribution poly(n-butyl acrylate) sample has been investigated via electron spin resonance (ESR) spectroscopy. The measurements were carried out in a wide temperature range: different dynamic regions have been recognized, and the coupling of the probe dynamics to the α and secondary relaxations has been revealed. In particular, the coupling with the structural relaxation is ruled by two fractionary Vogel-Fulcher laws (VF). The crossover from one VF region to the other occurs at the temperature T(C) = 1.17T(g), signalling the onset of the cooperativity in the dynamics and confirming a behaviour previously observed in ESR studies carried out on polymeric glass-formers. Furthermore, in this work we discuss the activated regime at the highest temperatures and show that the activation energy does not depend on the length of the polymer main- and side-chains, while its onset temperature linearly depends on the chain length.
authors.forename: Laura
authors.initials: L
authors.lastname: Andreozzi
authors.forename: Ciro
authors.initials: C
authors.lastname: Autiero
authors.forename: Massimo
authors.initials: M
authors.lastname: Faetti
authors.forename: Marco
authors.initials: M
authors.lastname: Giordano
authors.forename: Fabio
authors.initials: F
authors.lastname: Zulli