Dielectric Study of the Dynamics of Poly(oxyethylene) Chains in Triblock Copolymers:  Poly(oxyethylene)-b-polystyrene-b-poly(oxyethylene)

Abstract

Calorimetric, X-ray scattering, and optical microscopy measurements have been used to characterize the morphology of two PEO-b-PS-b-PEO copolymers. When the molecular weight of the PS block is much larger than the PEO one, the copolymer does not crystallize from the melt, and two well-separated glass transitions are clearly observed. The glass transition temperatures are different from those of the homopolymers; thus, phase segregation is not complete. For the case of blocks of similar molecular weight, the spherulites fill the whole sample, even if the degree of crystallinity is 60%; thus, the amorphous PS and PEO chains are sandwiched between the lamellae. The dynamics of the PEO chains has been studied by dielectric relaxation. In addition to the structural and the subvitreous relaxation modes, the crystalline copolymer shows a strong high-temperature relaxation that may be attributed to the Maxwell−Wagner interfacial process. It was found that the structure of the polymer does not affect the subvitreous process, but the structural relaxation is strongly dependent on whether the PEO chain is in an amorphous or crystalline sample. The temperature dependence of the relaxation times is compared with that reported in the literature for PS/PEO composites.

Dynamics of poly(methyl methacrylate)–montmorillonite nanocomposites: A dielectric study

“…Apart from giving rise to MWS relaxation, the addition of MMT nanoparticles has also been observed to influence the molecular relaxations of the polymer matrix [13] and [14]. It is noteworthy that a frozen dynamics has been associated with the layer of amorphous polymer neighboring a crystalline region in semicrystalline block copolymers [15] and [16]. This mechanism is another possible contributor to the observed behavior in this PMMA-MMT system.…”

Dynamical mechanical behavior of copolymers made of styrene and methyl methacrylate: Random, alternate and diblock copolymers

“…A second possibility for describing the E* results is to use an empirical function. This approach is frequently use in the analysis of the complex dielectric function 3* [11][12][13][14][15]. Taking into account that in DMTA experiments the mechanical strain and the stress play roles equivalent to those of the electrical displacement and of the electric field in the dielectric relaxation measurements, it can be concluded that the compliance D*Z1/ E* is the mechanical equivalent of 3* [24].…”

“…In the case of block copolymers, it has been found that the so-called normal mode of blocks such as poly(isoprene) or poly(propylene glycol) are different than in the corresponding homopolymers [10][11][12]. Also, the coexistence of an amorphous phase made of one of the comonomers, and a glassy or a crystalline phase formed by the other one may lead to the appearance of a rigid amorphous phase, with well differentiated dynamic properties [13][14][15]. Finally, the existence of concentration fluctuations lead to a broadening of the dynamic relaxations, similar to the one described in polymer blends [16].…”

Molecular Dynamics Simulation of Synthetic Polymers

“…The di-block copolymers in melt state have been studied by divers researcher groups, due to great interesting from the point view of the dielectric and dynamic-mechanics behavior (Alig et al, 1992;Encinar et al, 2008;Karatasos et al, 1996;Kotaka and Adachi, 1997;Kyritsis et al, 2000;Ma et al, 2003;Moreno and Rubio, 2002;Vogt et al, 1992). Dynamic-mechanical spectroscopy is an important technique to characterize the deformation of polymeric materials applying, for example, a tension to material.…”