Normal Mode Relaxation in Linear and Branched Polyisoprene

Abstract

Dielectric spectroscopy was carried out on linear and three-arm star polyisoprenes (PI). The shape of the normal mode peak differed significantly from the corresponding mechanical terminal relaxation function, although the temperature dependencies measured for the two spectroscopies were similar. This represents a departure from the usual correlation between time and temperature dependencies. In accord with mechanical relaxation data on these same polymers, the normal mode peak is found to be broader and more sensitive to temperature for star-branched PI than for the linear polymer.

Effect of temperature on the terminal relaxation of branched polydimethysiloxane

“…However, data obtained over a 120°range of temperature showed clearly that there is an enhancement of the temperature dependence, accompanied by a breakdown of timetemperature superpositioning [14,15]. These results were supported by normal mode dielectric spectroscopy [16]. A value of K ¼ 0:4 kJ/mol was obtained.…”

“…Previous assessments [9,[14][15][16] of the effect of branching on the temperature dependence relied on the assumption that the mechanism to alleviate constraints from entangled branches was a thermally activated process [8]. This means that an Arrhenius plot of terminal relaxation times or viscosities for a branched polymer, normalized by that of the corresponding linear species, would be linear (Eq.…”

“…More usually, enhancement of the temperature dependence is observed for polymers with wellentangled branches [9,11,12,[14][15][16], and it is accompanied by a breakdown of time-temperature superpositioning in the terminal zone. In this regard, the thermorheological simplicity seen in Fig.…”

Rheology of Star-Branched Polyisobutylene

“…On the other hand, the Graessley interpretation, while successfully describing the present results, fares less well in the case of branched 1,4-polybutadiene 20 and 1,4-polyisoprene. [25][26][27] Evidently, further experiments, with other branched polymers and higher molecular weight samples, are needed to clarify this situation. …”

Physico-mechanical and electrical properties of conductive carbon black reinforced chlorosulfonated polyethylene vulcanizates

“…Dielectric spectroscopy offers advantages to study the high frequency dynamics of polymers. Dielectric spectra reflect the same chain motions as the mechanical modulus; however it has reduced interference due to symmetry from shorter time process making it more accurate than the traditional dynamic mechanical analysis [35]. The 'electric modulus' formalism first introduced by McCrum et al [36] and extensively used for the investigation of relaxation phenomena in polymer composites by Tsangaris et al [37,38] can be defined as the inverse quantity of complex permittivity and is given by the following expression (Equation (6)):…”