Two calorimetric glass transitions do not necessarily indicate immiscibility: The case of PEO/PMMA

Abstract

Differential scanning calorimetry has been used to examine blends of a poly(ethylene oxide) (PEO), Mn = 300 g/mol, and a poly(methylmethacrylate) (PMMA), Mn = 10,000 g/mol, across the complete composition range. The relatively low molar mass of the PEO minimizes interference from crystallization. In the midrange of composition, ∼25–70% PEO, two broad, but distinct, glass transitions are resolved. These are interpreted as distinct glass transitions of the two components, as anticipated by the self‐concentration model of Lodge and McLeish. The composition dependence of the observed transitions is well described by the self‐concentration approach, using lengthscales of approximately two‐thirds of the Kuhn length. The results are compared with previous measurements on PEO/PMMA blends and other miscible systems. The principal, general conclusion is that one should actually expect two glass transitions in a miscible polymer blend or polymer solution; the rule of thumb that two transitions indicate immiscibility is incorrect. Furthermore, attempts to rationalize two transitions on the basis of incomplete segmental mixing, or other unspecified “nanoheterogeneity,” may not be justified in many cases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 756–763, 2006

Amorphous Polymer Blends: Recent Developments

“…Qualitatively, these experimental results support the self-concentration idea, in that individual polymer chain dynamics for the blend constituents should depend on the relative concentrations of each of the compo nents in the blend, as discussed in References [28,37] in which concentration dependent results were obtained based on variations in the amounts of each polymer in the blend. This does not mean that similar glass transition temperatures cannot exist for miscible blend components.…”

Effect of additives on the composition dependent glass transition variation in PS/PP blends

“…The T g values of individual blend components are often used as indicators of miscibility. 2 A single intermediate T g is observed in completely miscible blends and inward T g shifts are observed when there is partial miscibility between blend components. Immiscible blends are just mechanical mixtures of the constituent polymers and such blends generally do not show shifts in their T g , but rather reflect the properties of the neat components.…”

Scale-Dependent Miscibility of Polylactide and Polyhydroxybutyrate: Molecular Dynamics Simulations

“…Lodge et al 13 also suggested that the presence of two g T cannot be used as a criterion of immiscibility and semi-miscibility. A local increase in the self-concentration due to chain connectivity of polymers is an intrachain effect.…”