Abstract
Weight-average molecular weight () and its distribution of tetrafluoroethylene-hexafluoropropylene copolymers (FEP) were measured through dynamic melt viscoelastic tests. According to the Cox–Merz law and the four-parameter Carreau–Yasuda equation, the zero-shear viscosity could be obtained from the complex viscosity-frequency relationship. Then, the of FEP could be gained from the relationship of zero-viscosity and molecular weight. Based on Tuminello's theory, the curves of dynamic storage modulus (G′) vs. frequency (ω) could be transformed to a cumulative molecular weight distribution I(M), from which the weight-fraction differential molecular weight distribution (DMW) was obtained. Here, we gave a new function to estimate the front factor that relates frequency to molecular weight through basic rheological theory. Also, we gave a specific way to scale and normalize the differential distribution curves. Furthermore, when the DMW could be expressed by a three-parameter log-normal, like our samples, a very simple function was given to express the scaling factor, normalization factor, and polydispersity index. Additionally, it was also found that the polydispersity index was independent of scaling and the normalization factor.
Published Version
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