Modified Cole–Cole plot based on viscoelastic properties for characterizing molecular architecture of elastomers

Abstract

AbstractThe types of molecular architecture commonly present in many commercial elastomers include long branching, which in extreme cases results in crosslinked gel network. This architecture was modeled by preparing a series of ethylene–propylene copolymer samples in which the degree of branching was systematically varied. The frequency‐dependent viscoelastic properties of these model systems were measured over a temperature range of 80–230°C with a Rheometrics Mechanical Spectrometer. Time–temperature superposition was employed to obtain master curves of the storage G′ and loss G″ moduli and complex viscosity. The viscoelastic properties of the model samples change systematically with the variations in molecular architecture. Specifically, the low frequency Newtonian viscosity behavior is progressively replaced by non‐Newtonian power‐law behavior, and the G′ response relative to that of the G″ is significantly enhanced as long‐branching increases. The practical use of a modified Cole–Cole plot, in which the axes are expressed as the logarithms of G′ and G″, for analysis of molecular architecture is demonstrated. Changes in the long‐branch architecture of the model samples were readily detected as systematic variations in shape and displacement of the modified Cole–Cole plot. On the other hand, the data of molecularly linear elastomer samples of different Mw but similar MWDs were reduced to a single master Cole–Cole plot.