The Law of Polymerization Rate Decay

From the above results, it is clear that the rate decay must be attributed to a chemical deactivation of the polymerization centers with time. Different mathematical expressions have been proposed, for those catalyst systems most widely studied in the literature, in order to express the law of the decay. For propylene polymerization with TiCyMgCl2—AlEt3/EB or with TiCyEB/MgCl2 - Al Et3/EB, Spitz 45-97) proposed an expression of the following type  

However, this law has been verified only for a single polymerization temperature (62 °C), and has only an empirical meaning. 

Previously Keii and Doi had found, in the case of propylene polymerization in a slurry 98) or in the gas phase 99), a second order decay law  

Galli100) found that the kinetic curve, regarding propylene polymerization in a slurry under industrial conditions, can be adequately described by an expression of this type  

The kinetic curve would then be the result of two curves, one representing the 1st order decay attributed to isospecific polymerization centers, and the other representing a stationary state attributed to the less stereospecific centers. This expression can be credited with taking into consideration a stationary state and, furthermore, it is in agreement with the inverse correlation between productivity and isotacticity of the polymer found experimentally. In fact, assuming Is to be the isotacticity of propylene produced by the isospecific centers, unstable with time, and IA the isotacticity of polypropylene produced by the less specific centers, stable with time, the total isotactic index IIt is given by the expression  

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