DMAO-activated Rare-earth Metal Catalysts for Styrene and Its Derivative Polymerization

The catalytic performa nee of rare-earth metal dialkyl complexes in combi nation with DMAO(dry methylalumi no xane)is explored.In the presence of 60 equivalents of DMAO,the half-sandwich complex(C_(13)H_(8)CH_(2)Ph)Sc(CH_(2)SiMe_(3))_(2)(THF)(1)is inert for styrene polymerization,but(C_(5)Me_(4)Ph)Sc(CH_(2)C_(6)H_(4)NMe_(2)-o)_(2)(2)con verts 18% styre ne into syn diotactic polystyrene.Under the same conditi ons,the con strained-geometry configuration sandium complex(C13H8CH2Py)Sc(CH_(2)SiMe_(3))_(2)(3a)displays extremely high catalytic activity(>6420 kg·mol_(sc)^(-1)h^(-1))and perfect syndiospecific(rrrr>99%)for styrene polymerization,while its lutetium(3b)and yttrium(3c)analogues are nearly inactive.Although the binary catalytic system 3a/DMAO exhibits very low activity for 4-methoxystyrene polymerization,it is an efficient catalyst for the syndioselective polymerization of other styrene derivatives such as 2-methoxystyrene,4-methylthiostyrene,4-fluorostyrene,4-dimethylhydrosilylstyrene,alkyne-susbstituted styrenes and 4-methylstyrene.In addition,the binary system 3a/DMAO can copolymerize ethylene and styrene to give alternating copolymers with a single glass tran sition at 80℃ and 0.4 MPa ethylene pressures.By in creasing styrene feed amount from 20 mmol to 60 mmol,the styre ne con tent slight in creases from 48.2 mol% to 53.8 mol%,but the polymerizatio n activity is obviously promoted from 240 kg·mol_(Sc)^(-1)·h^(-1) to 532 kg·mol_(sc)^(-1)·h^(-1).