Copolymerizations of ethylene and α-olefins with supported piano-stool catalysts

Abstract

Recent developments in single-site catalysis (SSC) have led to many interesting discoveries in ethylene and α-olefin copolymerizations. Here, we report the synthesis of, and polymerizations with, supported piano-stool catalysts and their related analogues. CpTiCl 3, Cp*TiCl 3, TMSCpTiCl 3, and (TMS) 2CpTiCl 3 were covalently bound to a poly(styrene- r-4-hydroxystyrene) copolymer, affording macroligated catalysts. Ethylene/1-octene and ethylene/styrene copolymerizations with each of these supported catalysts were attempted with cocatalysts including methyl aluminoxane, B(C 6F 5) 3, [Ph 3C][B(C 6F 5) 4], and [PhN(CH 3) 2H][B(C 6F 5) 4]. To determine the effects that the macroligand and the substituents on the cyclopentadienyl ring have on polymer yield and activity, comonomer incorporation, polymer composition, molecular weight, polydispersity index, melting point, and crystallization behavior were investigated. We discovered that the catalysts have vastly different, yet interesting, effects on ethylene/1-octene (EO) and ethylene/styrene (ES) copolymerizations. For ethylene/1-octene copolymers, the activity of the supported catalysts and the amount of 1-octene incorporated into the copolymer is dependent upon the substituents on the cyclopentadienyl ring. The formation of EO copolymers using supported aryloxy-based cyclopentadienyl complexes can also be used as additional evidence for the presence of the tethered aryloxy moiety. The copolymer composition and the thermal properties of these copolymers were also studied. Ethylene/styrene copolymerizations produced polymers with varying characteristics specific to the catalyst employed for the polymerizations. Polymers synthesized with the supported CpTiCl 3 and TMSCpTiCl 3 displayed both polyethylene and syndiotactic polystyrene melting points. Conversely, polymers synthesized with the supported Cp*TiCl 3 displayed only a polyethylene melting point, while polymers prepared with the supported (TMS) 2CpTiCl 3 displayed only a syndiotactic polystyrene melting point. These findings suggest that copolymerization of ethylene and styrene is not possible with these catalysts. Analysis of the homopolymerizations of styrene and ethylene with Cp*TiCl 3 and (TMS) 2CpTiCl 3, respectively, shows significantly lower activities, leading to preferential polymerization of the more active monomer during copolymerization.