Thermophysical Properties and Molecular Relaxations in Cured Epoxy Resin + PEO Blends: Observations on Factors Controlling Miscibility

Abstract

Summary: Thermophysical properties and molecular relaxations in aromatic amine‐cured diglycidyl ether of bisphenol‐A (DGEBA) epoxy oligomer and poly(ethylene oxide) (PEO) mixtures were determined by DSC and dielectric techniques (TSC, DRS). The binary blends were judged to be fully miscible in the amorphous state (wPEO < 40 wt.‐%), as evidenced by the single composition‐dependent glass transition temperatures Tgs. In the amorphous blends, negative deviations of dielectric/thermal Tg‐estimates from the linear mixing rule or the behavior predicted by the Fox equation reveal weaker intermolecular interactions, compared to strong self‐association of hydroxyls in the cured thermoset. Morphological changes in PEO‐rich blends (wPEO ≥ 40 wt.‐%) are in accordance with their complicated interface structure, previously reported to consist of amorphous PEO regions, branched epoxy resin chains and an imperfect epoxy resin network located between PEO lamellae. In these blends, PEO crystallites exert steric hindrances in the amorphous regions, causing strong Tg upshifts. Changes in the relaxation dynamics of glyceryl segments (e.g., in the activation energy barrier and relaxation strength) are in accordance with the idea that the close matching between the molecular polarities of PEO, epoxy resin and the cure agent significantly contributes to the observed miscibility.

Cure kinetics, morphology and miscibility of modified DGEBA-based epoxy resin – Effects of a liquid rubber inclusion

“…However, there are several reports on DGEBA-based epoxy resin and elastomeric modified blends on immiscibility or miscibility depending on the structure of the curing agent. In a very recent interesting investigation by Kalogeras et al [30], aromatic amine-cured DGEBA epoxy resin and poly(ethylene oxide) (PEO) blends were analyzed by DSC and dielectric techniques to study the parameters controlling miscibility. In another recent work [31], miscibility parameters were analyzed by DSC for ternary thermosetting blends composed of epoxy resin, PEO, and poly(3-caprolactone) (PCL).…”

Intermolecular force and thermal properties of the sulfonyl epoxy blends cured with DGEBA epoxy

“…The backbone stabilization 42,43 The parameter q is related to the change in energies of the different mixture components system. The parameter q can be expressed as the following eq.…”

Dielectric Analysis (DEA)

“…For example, by increasing the size of the ester sidegroup R 2 (from methyl, to ethyl, n -propyl, n -butyl, etc. The signal shows a narrow relaxation time distribution and is dependent on the chain structure [e.g., by showing internal plasticization with increasing alkyl group length (Dudognon et al 2003(Dudognon et al , 2004] or dopants [e.g., by being antiplasticized -i.e., appearing at higher temperatures -in blends with dye molecules (Kalogeras et al 2006b(Kalogeras et al , 2007a]. At the same time, the α transitions are shifted to lower temperatures ( " internal plasticization " effect) and merge with the secondary signals (Hedvig 1977 ; Dudognon et al 2004 ).…”

“…Several relaxations have been isolated and comprehensively studied by dielectric as well as dynamic mechanical spectroscopy, and subsequently attributed (not always in a straightforward manner) to the amorphous or crystalline microphases in the material [e.g., see Sauer et al (1997) for information on the relaxation activity of POM]. Changes in the local molecular environment are possible by a number of means, including the use of highor low -molecular -weight diluents, crystallization (McGrum et al 1967 ), or interpenetrating network formation (Kalogeras et al 2006b(Kalogeras et al , 2007a. At somewhat lower temperatures, and only in selected polymers, the spectra show a normal -mode (n) relaxation (see Section 6.2.4.3 ).…”