We report the design, synthesis, and physical/ mechanical properties of graft copolymers containing semicrystalline polypropylene side chains and amorphous ethylene/α-olefin copolymer backbones. These materials, a new class of semicrystalline, polyolefin-based thermoplastic elastomers, are made in two steps. First, allyl-terminated syndiotactic or isotactic polypropylene macromonomers are synthesized with controlled microstructure and molecular weight using bis(phenoxyimine)-titanium or chiral ansa-zirconocene catalysts, respectively. Second, a pyridyl-amido hafnium catalyst is used to copolymerize the macromonomer, ethylene, and an α-olefin with precise control of composition and side chain incorporation. With highly crystalline polypropylene side chains and amorphous backbones of low glass-transition temperatures (<−55°C), the samples have strain-to-break values up to 1400% and elastic recovery above 85% at maximum strains up to 1000%. The synthetic method described herein does not require the use of a living polymerization catalyst; in addition, the mechanical properties of these graft copolymers exceed those of the best linear block polyolefins.T hermoplastic elastomers (TPEs) are an important class of industrial materials that are an attractive alternative to vulcanized rubber. 1 TPEs can be melt-processed, do not require vulcanization, and, unlike thermoset rubbers, can be recycled. TPEs are blocky polymers that derive their elastomeric properties from a combination of "hard" segments with high melting points (T m ) or high glass-transition temperatures (T g ) and "soft" segments with low T g . Elastomeric properties can be obtained in structures having at least two hard sequences separated by a soft sequence and are typically linear triblock or multiblock copolymers. In the solid state, the hard segments are dispersed throughout the amorphous matrix and form physical cross-links that produce recoverable elasticity after straininduced deformation. 1 A well-known example of a commercial TPE is a triblock polystyrene-block-poly(ethylene-co-butene)-block-polystyrene copolymer (SEBS). Although many commercial TPEs are prepared via anionic polymerization and contain polystyrene, there has been longstanding interest in the synthesis and properties of TPEs based on other monomers. Bates and co-workers prepared model polyolefin TPEs by anionic polymerization followed by hydrogenation. 2 More recently, bio-derived TPEs have been reported. 3Given the low cost of ethylene, propylene, and α-olefins, considerable academic and industrial efforts have focused on the development of catalysts and reaction conditions to prepare blocky polyolefins. 4 Several approaches are shown in Scheme 1. Early efforts focused on elastomeric polypropylene (Scheme 1A) prepared with nonliving catalysts. Natta reported the first elastomeric polypropylene in 1959 using TiCl 3 /AlR 3 catalyst mixtures, 5 and more recently similar materials were obtained using zirconium and titanium alkyl complexes supported on alumina. 6 In the 1990s, the synth...

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The particle morphology of impact polypropylene was examined experimentally in order to understand how the rubber phase produced in the second step of the polymerisation is distributed inside the growing polymer particles, and how the quantity of rubber produced influences the overall morphology of the final product. flow out of the large pore openings on the surface of the particles. A possible mechanism for the distribution of rubber was proposed.

Bridged zirconocenes bearing seven-membered rings dichlorodimethylsilylenebis(2-methyl-4-phenyl-4-H-azulenyl)zirconium (3a) and dichlorodimethylsilylenebis(2-methyl-4-phenyl-4-H-5,6,7,8-tetrahydroazulenyl)zirconium (4) were synthesized. A silylene-bridged ligand was obtained by the reaction of 2-methylazulene, phenyllithium, and dichlorodimethylsilane. After lithiation of the ligand by n-butyllithium, reaction with zirconium tetrachloride gave a rac and meso mixture of 3. The structure was confirmed by X-ray crystallographic analysis. It was found that both of the phenyl groups at the 4-position are oriented outside toward the metal center and the seven-membered ring is not planar. Furthermore, reaction with hydrogen in the presence of platinum oxide gave 4. When activated with methylaluminoxane, these complexes showed high catalytic activity for polymerization of propene to give isotactic polypropylene.

Copolymerization of propene with 1-hexene was performed at 40 "C under atmospheric pressure using both aspecific and isospecific catalysts composed of TiCI,/MgCl, and AI(C,H,),, and of Solvay type TiCl, and Cp,Ti(CH,), (Cp: cyclopentadienyl), respectively. The isospecific catalyst gave two kinds of copolymers with different content of 1-hexene, whereas the aspecific catalyst gave a uniform copolymer abundant in 1-hexene. Both copolymers produced with the isospecific catalyst were found to show isotactic stereoregulation in the propylene units. From these results, it was concluded that the catalyst composed of Solvay type TiCI, and Cp,Ti(CH,), has two kinds of isospecifically active species which differ in the monomer reactivity ratio for propene-1 -hexene copolymerization.