The structure of isotactic polypropylene, obtained by means of Ziegler-Natta catalysis, can be characterized only by molecular weight distribution. The mechanism of stereospecific catalysis eliminates other variables, i.e., short and long branching. In this case it is possible to develop a rheological study dependent only by polydispersity. The spectrum of relaxation times of five samples of polypropylene have been calculated from swelling measurement in the molten state and from flow master curves. The molecular weight distribution of the samples has been calculated by means of the relaxation spectrum, as suggested by Ferry. This information has been compared with that obtained by a fractionation method. There is a good agreement between the calculated and measured polydispersity curves. 946 ( 1961). C) SWELLlNG io5 406 M 407 Fig. 13. Molecular weight distribution function calculated from Eqs. 16 and 17, using H(lnt) determined from (A) viscosity data and Eq. 11, (C) swelling data and Eq. 7 . Curve B gives the distribution measured by fractional elution. Results for sample C.
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