Stereoelective coordination catalyst

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... 

In conclusion, i lle It Is evident that much has been learned about reactions producing polyethers and important factors which affect them, there remain Intriguing unanswered questions. While there has been much speculation, it Is not clear that we know in any detail the structural features of stereoselective and stereoelective coordination catalysts for epoxide polymerization. 

Polymerisations of tiiranes in the presence of coordination catalysts containing multinuclear species have been extensively studied in terms of their stereoselective and stereoelective behaviour. For monosubstituted tiiranes, the polymerisation can proceed enantiosymmetrically and lead to a mixture of isotactic chains of opposite configurations. By using optically active catalysts, the polymerisation may occur enantioasymmetrically, with the enchainment of only one of the two enantiomers. 

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