Stereoelective polymerization mechanism

Further investigations are necessary to clarify the mechanism of stereoregulation in the polymerization of olefins and diolefins probably the stereoelective polymerization of vinyl monomers and the asymmetric polymerization of diolefinic compounds will give further interesting contributions to the future progresses in this field. 

In a previous paper presented by Dr, Leborgne and Spassky, from the Universite Pierre et Marie Curie, in Paris, it has been shown that it is now possible to prepare optically active polylactones by a "stereoelective" polymerization process. It is the purpose of the present paper to indicate important differences in properties between the optically active and the racemic poly(a-methyl-a-n-propyl-3-propiolactone) (PMPPL). Results will be presented concerning the crystallization and melting properties, as well as the dynamic and transient mechanical properties of these polymers. 

An interesting consequence of the mechanism of stereoelective polymerization of f-butyl thiirane is the possibility of preparing optically pure polymers starting from a racemic mixture as indicated in the last scheme. 

Different independent approaches were used to investigate the mechanism of polymerization of a-olefms with heterogeneous catalysts. As a result, it was shown that isotactic polymerization of racemic mixtures of a-olefms are stereoselective. Also, optically active polymers form with optically active catalysts.Stereoelectivity and stereoselectivity are due to the intrinsic asymmetry of the catalytic centers. This conclusion comes in part from knowledge that propylene coordinates... 

It can be concluded that studies of a subtle elements of propagation, particularly in the coordinated processes, are still needed. Perhaps the advanced quantum mechanical calculations methods would be very helpful for this purpose. The p-substituted p-lactones are still waiting for the stereospecific initiator allowing the stereoelective and/or stereoselective polymerizations to be carried out. Finally, initiators of the stereocontrolled polymerization operating in bulk, high-temperature processes are also wanted. 

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