Random chain scission 678 INDEX

Shape of the variation of poiydispersity index (Pi) as a function of ageing time for a iinear poiymer undergoing a random chain scission (a) Pio > 2 (b) Pio < 2. 

Zeichner and coworkers [33,34] developed a measure of the breadth of the molecular weight distribution that is based on the curves of storage and loss moduli versus frequency. Based on data for a series of polypropylenes made by Ziegler-Natta catalysts and degraded by random chain scission, they found that the polydispersity index, i.e., the ratio Af /M , was related to the crossover modulus, G, as shown in Eq. 5.8... 

In a paper published in 1959 [26] Charlesby and Pinner developed the Charlesby-Pinner equation which allows the experimentalist to determine the G(S) and G(X) ratios. The derivation of the equation is based on an initial random molecular weight distribution and relates to the sol firaction, s, to the crosslinking index, y, when both main chain scission and crosslinking occur. 

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