Theoretical Mechanistic Studies of the Polymerization of Functionalized Styrenes Catalyzed by Rare-Earth-Metal Complexes: Stereoselectivity Regulation

The polymerization mechanism of amino-functionalized styrene catalyzed by different cationic rare-earth-metal catalysts [(C5H5)­Sc­(NMe2CH2C6H4-o)]+ (Sc-1) and [(C5Me4SiMe3)­Sc­(NMe2CH2C6H4-o)]+ (Sc-2) has been evaluated by density functional theory (DFT) calculations. Having achieved an agreement between theory and experiment, it was found that apparent steric hindrance is the main reason the two catalysts can facilitate the polymerization of the same monomer (N,N-dimethylamino) styrene (DMAS) (a), while the stereoselectivity of polymerization over catalysts Sc-1 and Sc-2 was atacticity and syndiotacticity, respectively. Moreover, as a result of the C–H···π interactions of monomer (N,N-diphenylamino) styrene (DPAS) (b) with the catalyst, the amino-functionalized syndiotactic polystyrene was produced by Sc-1. In addition, such a regulation manner was theoretically demonstrated by studying the polymerization of various amino-functionalized styrene monomers, and the obtained results showed that the stronger the C–H···π interactions, the higher the syndiotactic selectivity of the catalyst.