Temperature Dependence of Mechanical and Dielectric Relaxation in cis-1,4-Polyisoprene

Abstract

The linear viscoelastic properties of 1,4-polyisoprene (PI; M W = 504 000) were measured by combined mechanical and dielectric spectroscopies. For local segmental motion, the respective mechanical and dielectric relaxation times, although differing substantially in magnitude, have identical temperature dependencies. The shape of the segmental relaxation function itself was sensitive to temperature. The data, obtained over a 160 degree range of temperatures, could be reduced to yield ostensibly satisfactory master curves; however, detailed analysis reveals the usual breakdown of time−temperature superpositioning in the glass transition zone. Given the near equivalence of the respective breadths of its terminal and segmental dispersions, thermorheological complexity in PI is unanticipated by theory. In the plateau zone, the mechanical spectrum of PI exhibits power law behavior, with an exponent (0.21) close to a proposed universal value.

Birefringence of Polymers in the Softening Zone

“…We also note that for both measures of the position in the spectrum at which the glassy component's contribution becomes negligiblesD(t) attaining a value 4 times higher than the glassy compliance 3,12-14 (largedashed line in Figure 2) and decay of the local segmental relaxation function to zero 15 (short-dashed line in Figure 2)seqs 15-20 indicate dominance of the rubbery component. Thus, the assumption of strain additivity enables the experimental data to be accurately reproduced and the deduced contributions of the glassy and rubber components are consistent with alternative methods of assessing their relative significance.…”

“…3,[12][13][14] (iv) As determined by dielectric spectroscopy, the local segmental relaxation decays to zero near the middle of the transition zone. 15 These results should prompt reexamination of the assumption of stress additivity and any inferences derived from it.…”

Anomalous Behavior in Blends of a Polychlorinated Biphenyl with Polystyrene Oligomer Investigated by Mechanical and Dielectric Spectroscopy

“…Because the difference between τ(M′′) and τ( ′′) depends on the dielectric strength, the relative magnitudes for the two spectroscopies vary for different materials. [5][6][7][8][9][10] A useful approach to assess the dynamics of glass formers is by comparison of their T g -normalized temperature dependences. The steepness of such T g -scaled Arrhenius plots ("fragility") provides a means to classify the behavior of different glass formers.…”

Comparison of the transient stress–strain response of rubber to its linear dynamic behavior

“…This is a wellknown effect of the increasing contribution of the segmental dynamics, as temperature is decreased. 36,[41][42][43][44][45][46][47] The segmental modes have a stronger temperature dependence than the chain modes, and in the transition zone both influence the response. Nevertheless, the a T are valid for superposition of the rubbery response up through the onset of this glass transition.…”