Abstract

AbstractThe shape of the dynamic moduli vs. temperature curves of polymers fundamentally depends on the temperature dependence of the relaxational properties of the polymers. When the frequency dependence of the reduced loss modulus is represented by an empirical function describing the dispersion peak, the distribution of the relaxation times and the storage modulus vs. frequency curve corresponding to that peak can be calculated. The temperature dependence of the reduced moduli can then be expressed as a function of the activation energy of the relaxation process and of a single parameter describing the width of the relaxational distribution function. This analysis is useful for a better understanding of the loss modulus vs. temperature spectrum and is applied to a linear polyethylene. Furthermore, a discussion is given of the differences in the spectra of linear polyethylenes and polypropylenes, mixtures of polyethylene and polypropylene, and copolymers of ethylene and propylene. When ethylene is randomly built into a polypropylene chain, the β‐transition of polypropylene is shifted to lower temperatures over a distance which is determined by the ethylene content. No shift is observed in mixtures of polyethylene and polypropylene. Here, the β‐peak of the loss modulus vs. temperature spectrum is only lowered and its height is a measure of the amount of amorphous polypropylene. The height of the loss modulus in the α‐region is determined by the total fraction of crystalline material in the mixture, the height of the γ‐peak is proportional to the ethylene content. The loss modulus spectrum can, to a large extent, be used for distinguishing between these different polymers.

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