Secondary and Segmental Relaxation in Polybutadienes of Varying Microstructure:  Dielectric Relaxation Results

Abstract

The dielectric behavior of polybutadiene copolymers with different compositions of 1,2 and 1,4 units is analyzed to study the influence of the microstructure on the relaxation spectrum, especially the β relaxation. The experimental data were obtained between 10-2 and 106 Hz and temperatures above and below T g. Above T g, the relaxation spectra are described by the superposition of two processes, the main α relaxation at low frequencies and a β relaxation at high frequencies. The α relaxation has the typical Vogel−Fulcher−Tammann behavior and exhibits a quasi-linear shift of time scale upon change of the vinyl content. The high-frequency process shows Arrhenius behavior only in the case of the homopolymers. For the other samples with a mixture of microstructures, spectral broadening occurs and deviation from the Arrhenius behavior is observed. In these samples, the relaxation can be modeled by the simple assumption that the high-frequency process consists of a superposition of two separate processes, each with the properties of the β relaxation of one of the homopolymers. This suggests that secondary relaxations can relax quite independently from the segmental relaxation and are therefore restricted to a very local environment influenced by intramolecular interaction.

Unified application of the coupling model to segmental, Rouse, and terminal dynamics of entangled polymers

“…1. The VFTH parameters which capture these data are A a = 6.607 · 10 À15 s, B a = 1214 K, and T 1,a = 139.1 K. In a similar manner, dielectric results from Hofmann et al [31] and Colmenero et al [32] were combined with dynamic shear data [26] for 1,2-polybutadiene (1,2-content > 93%) as shown in Fig. 2.…”

Positron annihilation and relaxation dynamics from dielectric spectroscopy and nuclear magnetic resonance: Cis–trans-1,4-poly(butadiene)

“…The first possibility has already been discussed in Ref. 26 in connection with dielectric work on the similar c-t-1,4-PBD sample, 45 where on the basis of the dielectric β DS relaxation time distribution G[log τ β (T )] slightly extrapolated toward lower T's some of us tentatively proposed that this slight bend effect could be associated with a high-f tail of the slow secondary β DS process. As for the second hypothesis, the scattering intensity coming from the harmonic motion of the H atoms in low-T region and any nonelastic contribution from various types of the H-mobility at higher temperatures can be measured by elastic and quasi-elastic neutron scattering (NS) experiments.…”

“…On the other hand, the fully amorphous PBD polymer can be obtained under special synthesis conditions of anionic polymerization with the appropriate combinations of the major cis-and trans-isomer and minor vinyl-isomer microstructures giving cis-trans-1,4-poly(butadiene)s (c-t-1,4-PBD). 41 A number of structural 42 and especially, dynamic methods such as rheology, 43 dynamic neutron scattering (NS), 44 BDS, 45 and dynamic light scattering (LS) (Ref. 46) have been used in investigations of these PBD's.…”

Segmental Relaxation of Poly(styrene-co-vinylphenol)

“…[7][8][9][10][11][12][13][14][15] In this paper we describe dielectric and mechanical measurements on polystyrene copolymerized with varying levels of vinylphenol. The hydrogenbonding capacity of the latter enhances miscibility, leading to a number of interesting blends.…”