Polybutadiene dielectric relaxation

Dynamics Simulation Study of Dielectric Relaxation in a 1,4-Polybutadiene Melt. 

Polystyrene and polybutadiene homopolymers as well as random and block copolymers of these mers have been studied via dielectric relaxation spectroscopy and tensile stress-strain measurements. The results suggest that some block copolymer systems studied have styrene rich surfaces which appear to partially crosslink upon initial exposure to ozone even though surface oxygen concentrations are not significantly affected. After continued exposure these samples appear to then undergo chain scission. Complex plane analysis implies that after degradation... 

Figure 2. The a-p relaxation bifurcation in the case of the polymer polybutadiene as observed in inelastic neutron scattering( ) and dielectric relaxation (open symbols A, ). Note that the bifurcation temperature accords with the MCT Tc, as in the case of molecular liquids. Tc/To(vfT) is 1.69 in this case[26], or 1.59To if To is taken to be Tg-50. (reproduced form ref. 26, by permission).

We now turn from binary polymer solvent systems to ternary polymer matrix solvent systems. Dielectric relaxation studies using polyisoprenes as probe chains in polybutadiene -heptane solutions were examined by Urakawa,... 

Figure 7.16 Dielectric relaxation spectrum of a 47.7 kDa Mw di-polyisoprene having nonparallel dipoles due to one inversion at the molecular center, dissolved in 700 Da polybutadiene at a concentration of 27 g/1, using original measurements by Watanabe, etal.Cil), with simple-exponential and power-law fits.

Figure 7.17 Dielectric relaxation spectrum of a 21 kDa triblock copolymer (58 g/1 in hexadecane) in which the central 3 kDa is the type-A c -polyisoprene and the two terminal ends are 8 kDa dielectrically inert polybutadienes, using original measurements by Adachi, et al.(2). The high- and low-frequency features are here interpreted as segmental motion and whole-chain reorientation, respectively.

Figure 17. Dielectric loss data of 1,2-polybutadiene (1,2-PBD) at various combinations of temperature and pressure as indicated to demonstrate the invariance of the dispersion of the a-relaxation at constant a-loss peak frequency va or equivalently at constant a-relaxation time ra.

For rubbers such as NR (or synthetic 1,4-polyisoprene) (Santangelo and Roland, 1998) and polybutadiene (both 1,2- and 1,4-isomers) (CareUa et al., 1986), LCB increases the temperature sensitivity of the viscosity and terminal relaxation time. Thus, by comparing apparent activation energies, or, in the more usual case where the behavior is non-Arrhenius, the temperature dependence of the ratio of relaxation times for an unknown and a linear sample of the same polymer, inferences can be drawn concerning LCB (Figure 3.9). For polymers such as 1,4-polyisoprene, which have a dipole moment parallel to the chain, dielectric measurements of the normal mode can be used to measure the temperature dependence and thus assess the presence of LCB. 

O. Urakawa, K. Adachi, and T. Kotaka. Dielectric normal mode relaxation of probe polyisoprene chain in semidilute polybutadiene solutions. 1. End-to-end distances. Macromolecules, 26 (1993), 2036-2041. 

---