Influence of Morphology on the Dynamics of the PB Glass Process in SBS

Abstract

The molecular dynamics of two styrene-butadiene-styrene block copolymers with different morphologies and stiffness but with the same phase dimensions (thickness of domains) were investigated. Dynamic mechanical and dielectric measurements were done over wide ranges of frequencies, 10–4–10 Hz and 0.1–105 Hz, and temperatures from –95°C to –17°C and from –93°C to –72°C, respectively. In addition, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and stress-strain behavior investigations were also used in the characterization. The dielectric and dynamic mechanical results showed that the dynamics of the glass process of the polybutadiene phase (PB phase)in both polymers is the same. Therefore, it could be concluded that the difference in morphology does not influence the dynamics of the glass process of the polybutadiene phase in these materials, where the geometrical confinement applied on the PB phase is the same in both polymers. Fitting of the activation curves of the glass process, to evaluate the length of the cooperative reorienting region of the PB phase, delivered a length of 10.3 nm. This result means that the domains seen by TEM (9 & 20 nm) are formed either from one or by association of two structural units (≈ 10 nm).