Chain structure, aggregation state structure, and tensile behavior of segmented ethylene-propylene copolymers produced by an oscillating unbridged metallocene catalyst.

Segmented ethylene-propylene copolymers (SEPs) with different propylene contents were prepared by an unbridged metallocene bis(2,4,6-trimethylindenyl)zirconium dichloride [(2,4,6-Me3Ind)2ZrCl2] catalyst. Due to oscillation of the unbridged ligands in the catalyst, the SEPs are composed of segments with low propylene contents, alternated by the segments with high propylene contents. Such a chain structure was verified by (13)C NMR and successive self-nucleation and annealing (SSA). As the propylene/ethylene feed ratio during copolymerization increases, the comonomer contents in both segments are increased, leading to noncrystallizability of the high propylene segments and smaller crystallinity of the low propylene segments. Consequently, SEPs may be used as thermoplastic elastomers (TPEs). The aggregation state structures at nano- and micro-scales were characterized with small angle X-ray scattering, transmission electron microscopy and polarized optical microscopy, and compared with those of ethylene-octene multiblocky copolymers (OBCs) with similar crystallinity. It is found that SEPs form thinner lamellar crystals with a lower melting temperature due to shorter length and higher comonomer content of the low propylene segments. Moreover, the short length of the high propylene segments in SEPs results in an evidently thinner amorphous layer among the lamellar crystals, thus lots of amorphous phases are excluded out of the interlamellae. Accordingly, ill-developed spherulites or even bundle crystals are formed in SEPs, as compared with the well-developed spherulites in OBCs. SEPs exhibit the tensile property of typical TPEs with diffused yielding and large strain at break.

Synthesis and application of binuclear α-diimine nickel/palladium catalysts with a conjugated backbone.

A series of binuclear nickel/palladium catalysts C4-C7 with conjugated α-diimine ligands were designed, prepared and fully characterized. The binuclear nickel complexes C6 and C7 were activated by modified methylalumoxanes (MMAO) to generate highly active ethylene polymerization catalysts with activities up to 1050 kg [mol (Ni) h](-1). The activity of C7 is twice that of the mononuclear analogue under the same conditions. The effects of the catalyst structure, cocatalyst ratio, polymerization time, solvent and feeding monomer on the catalytic activities, molecular weight and branching structures of the resulting polymers were evaluated. The binuclear palladium complexes C4-C5 produced polyethylene with two separate peaks in GPC curves in ethylene polymerization. In contrast, the mononuclear analogue C3 produces polyethylene with a unimodal GPC curve. Probably, two active species are generated in the binuclear palladium catalyst system and are responsible for the bimodal feature of the GPC curves. The performance of the binuclear palladium complexes in ethylene/methyl acrylate copolymerization was also investigated.