?- and ?-Relaxations in neat and antiplasticized polybutadiene

Abstract

Dielectric spectroscopy was carried out to measure the α‐relaxation (local segmental motion) and the higher frequency, secondary relaxation (β‐mode) in 1,4‐polybutadiene, both neat and containing a nonpolar diluent, mineral oil. The α‐relaxation shifted to lower frequencies (antiplasticization) in the presence of the diluent, suggesting the glass temperature of the latter is higher than the Tg of the polymer (i.e., >187K). The Tg of neat mineral oil cannot be determined directly, due to crystallization. While the diluent increased the magnitude of the α‐relaxation times, it had no effect on the β‐relaxation. Moreover, neither the shape of the α‐relaxation function nor its temperature dependence was influenced by the diluent. From this we conclude that the main effect of the mineral oil was to increase the local friction, without changing the degree of intermolecular cooperativity of the molecular motions. We also find that near the glass temperature, there is rough agreement between the time scale of the secondary relaxation process and the value of a noncooperative relaxation time estimated from theory. This approximate correspondence between the two relaxation times also holds for 1,2 polybutadiene. However, the β‐process cannot be identified with the noncooperative α‐relaxation, and the relationship between them is not quantitative. © 2000 John Wiley & Sons, Inc.* J Polym Sci B: Polym Phys 38: 1841–1847, 2000

Verifying the Approximate Coinvariance of the α and Johari–Goldstein β Relaxation Times to Variations of Pressure and Temperature in Polyisoprene

“…Moreover, f β of 158 and 0.1 MPa are about 1 and 1.5 decades, respectively, lower than f 0 . These findings are consistent with relation , which states since 1998 − that the JG β-relaxation is not the same as the primitive relaxation, and hence the agreement between f β and f 0 is in order of magnitude only. The relation between the two relaxations comes from the following view of the evolution of dynamics with time. ,, At short times, molecules are mutually caged.…”

Verifying the Approximate Coinvariance of the α and Johari–Goldstein β Relaxation Times to Variations of Pressure and Temperature in Polyisoprene

“…Moreover, f β of 158 and 0.1 MPa are about 1 and 1.5 decades, respectively, lower than f 0 . These findings are consistent with relation , which states since 1998 − that the JG β-relaxation is not the same as the primitive relaxation, and hence the agreement between f β and f 0 is in order of magnitude only. The relation between the two relaxations comes from the following view of the evolution of dynamics with time. ,, At short times, molecules are mutually caged.…”

Clarifying the Molecular Weight Dependence of the Segmental Dynamics of Polybutadiene

“…The PB data do not fall far from the calculated line; however, taken alone there is almost no variation of τ β with β KWW , whereas the model predicts these τ β should vary by about a factor of 0.7 decade for these samples. In this respect the results are similar to an earlier study 55 in which addition of plasticizer to PB reduced T g and thereby substantially reducing τ R ; however, there was no significant change in either β KWW or τ β .…”

The α and Johari–Goldstein Relaxations in 1,4-Polybutadiene: Breakdown of Isochronal Superpositioning

“…Moreover, the behavior reported herein is directly evident in the isochronal spectra, obviating the need to extract relaxation times by fitting the dielectric spectra. The results are consistent with an increasing separation in time scales of the JG and α processes upon addition of antiplasticizer to PBD . An implication of our finding is that if both relaxations exhibit density scaling, their respective scaling exponents will differ.…”

“…This means that the respective scaling exponents cannot be the same. This experimental result is consistent with an earlier study in which slowing down of the α process in PBD through the addition of antiplasticizer (high- T g diluent) did not lead to any change in τ JG (although the JG relaxation times were only measured in the glassy state) . Measurements of secondary relaxations in binary mixtures of glasses suggest behavior at odds with eqs and , , although interpretation of the experimental results has been questioned .…”

Verifying the Approximate Coinvariance of the α and Johari–Goldstein β Relaxation Times to Variations of Pressure and Temperature in Polyisoprene

“…Moreover, f β of 158 and 0.1 MPa are about 1 and 1.5 decades, respectively, lower than f 0 . These findings are consistent with relation , which states since 1998 − that the JG β-relaxation is not the same as the primitive relaxation, and hence the agreement between f β and f 0 is in order of magnitude only. The relation between the two relaxations comes from the following view of the evolution of dynamics with time. ,, At short times, molecules are mutually caged.…”

Clarifying the Molecular Weight Dependence of the Segmental Dynamics of Polybutadiene

“…The PB data do not fall far from the calculated line; however, taken alone there is almost no variation of τ β with β KWW , whereas the model predicts these τ β should vary by about a factor of 0.7 decade for these samples. In this respect the results are similar to an earlier study 55 in which addition of plasticizer to PB reduced T g and thereby substantially reducing τ R ; however, there was no significant change in either β KWW or τ β .…”

The α and Johari–Goldstein Relaxations in 1,4-Polybutadiene: Breakdown of Isochronal Superpositioning

“…Moreover, the behavior reported herein is directly evident in the isochronal spectra, obviating the need to extract relaxation times by fitting the dielectric spectra. The results are consistent with an increasing separation in time scales of the JG and α processes upon addition of antiplasticizer to PBD . An implication of our finding is that if both relaxations exhibit density scaling, their respective scaling exponents will differ.…”

“…This means that the respective scaling exponents cannot be the same. This experimental result is consistent with an earlier study in which slowing down of the α process in PBD through the addition of antiplasticizer (high- T g diluent) did not lead to any change in τ JG (although the JG relaxation times were only measured in the glassy state) . Measurements of secondary relaxations in binary mixtures of glasses suggest behavior at odds with eqs and , , although interpretation of the experimental results has been questioned .…”

Verifying the Approximate Coinvariance of the α and Johari–Goldstein β Relaxation Times to Variations of Pressure and Temperature in Polyisoprene

“…Moreover, f β of 158 and 0.1 MPa are about 1 and 1.5 decades, respectively, lower than f 0 . These findings are consistent with relation , which states since 1998 − that the JG β-relaxation is not the same as the primitive relaxation, and hence the agreement between f β and f 0 is in order of magnitude only. The relation between the two relaxations comes from the following view of the evolution of dynamics with time. ,, At short times, molecules are mutually caged.…”

Clarifying the Molecular Weight Dependence of the Segmental Dynamics of Polybutadiene

“…The PB data do not fall far from the calculated line; however, taken alone there is almost no variation of τ β with β KWW , whereas the model predicts these τ β should vary by about a factor of 0.7 decade for these samples. In this respect the results are similar to an earlier study 55 in which addition of plasticizer to PB reduced T g and thereby substantially reducing τ R ; however, there was no significant change in either β KWW or τ β .…”

The α and Johari–Goldstein Relaxations in 1,4-Polybutadiene: Breakdown of Isochronal Superpositioning

“…Moreover, the behavior reported herein is directly evident in the isochronal spectra, obviating the need to extract relaxation times by fitting the dielectric spectra. The results are consistent with an increasing separation in time scales of the JG and α processes upon addition of antiplasticizer to PBD . An implication of our finding is that if both relaxations exhibit density scaling, their respective scaling exponents will differ.…”

“…This means that the respective scaling exponents cannot be the same. This experimental result is consistent with an earlier study in which slowing down of the α process in PBD through the addition of antiplasticizer (high- T g diluent) did not lead to any change in τ JG (although the JG relaxation times were only measured in the glassy state) . Measurements of secondary relaxations in binary mixtures of glasses suggest behavior at odds with eqs and , , although interpretation of the experimental results has been questioned .…”