Discrete, Multiblock Isotactic–Atactic Stereoblock Polypropene Microstructures of Differing Block Architectures through Programmable Stereomodulated Living Ziegler–Natta Polymerization

Harney, Matthew B.; Zhang, Yonghui; Sita, Lawrence R.

doi:10.1002/anie.200600027

Cited by 137 publications

(105 citation statements)

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“…Busico (15), Coates (16), and Sita (17) have reported group IV catalysts with varying degrees of isospecificity and livingness for the synthesis of iPP block copolymers. Notably, Sita (17) has recently reported the synthesis of elastomeric multiblock polymers with atactic PP and iPP segments. Coates (18) has recently reported a chiral nickel alpha-diimine catalyst that produces di-and elastomeric triblock polypropylenes with isotactic and regioirregular (rPP) PP blocks, controlled by the polymerization temperature.…”

Section: Block Polyolefinsmentioning

confidence: 99%

Semicrystalline thermoplastic elastomeric polyolefins: Advances through catalyst development and macromolecular design

Hotta

Cochran

Ruokolainen

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

123

116

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We report the design, synthesis, morphology, phase behavior, and mechanical properties of semicrystalline, polyolefin-based block copolymers. By using living, stereoselective insertion polymerization catalysts, syndiotactic polypropylene-blockpoly(ethylene-co-propylene)-block-syndiotactic polypropylene and isotactic polypropylene-block-regioirregular polypropyleneblock-isotactic polypropylene triblock copolymers were synthesized. The volume fraction and composition of the blocks, as well as the overall size of the macromolecules, were controlled by sequential synthesis of each block of the polymers. These triblock copolymers, with semicrystalline end-blocks and mid-segments with low glass-transition temperatures, show significant potential as thermoplastic elastomers. They have low Young's moduli, large strains at break, and better than 90% elastic recovery at strains of 100% or less. An isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene pentablock copolymer was synthesized that also shows exceptional elastomeric properties. Notably, microphase separation is not necessary in the semicrystalline isotactic polypropylenes to achieve good mechanical performance, unlike commercial styrenic thermoplastic elastomers.block copolymer ͉ polypropylene T he applications of a polymer are largely determined by its chemical, physical, and mechanical properties. These properties are in turn determined by polymer morphology, which is dictated by polymer structure and composition. Thermoplastic elastomers are a classic example where polymer architecture engenders unique properties. Block copolymers that contain at least two blocks that are hard at room temperature, separated by blocks with a glass transition temperature (T g ) below room temperature, typically exhibit elastomeric properties if the low T g block volume is large (1-5). The most well known elastomers of this type are the polystyrene (PS)-block (b)-polybutadiene-b-PS triblock copolymers, sold commercially by Kraton Polymers. Such materials normally possess a microphase-separated morphology in which 10-nm-scale domains of the hard blocks (e.g., PS) are embedded as spheres or cylinders within a continuous phase of the low T g soft blocks. The hard domains serve as thermally reversible crosslinks that at room temperature produce high levels of recoverable elasticity in the soft phase.Sequence control of a synthetic polymer is most easily accomplished by using a synthetic technique that allows the sequential addition of one or more monomers to the macromolecule in a chain growth process without spontaneous termination. These techniques are collectively called living polymerizations, and despite many successes over the last half century, their further development remains one of the most important frontiers in polymer science. In the case of the Kraton triblock copolymers, a living anionic polymerization process is used to synthesize the materials. Because approximately t...

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Section: Block Polyolefinsmentioning

confidence: 99%

Semicrystalline thermoplastic elastomeric polyolefins: Advances through catalyst development and macromolecular design

Hotta

Cochran

Ruokolainen

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

123

116

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“…In principle, the H 2 -generating (mechanism A) and alkanegenerating (mechanism B) paths could be distinguished by examination of the products: H 2 is an expected byproduct of mechanism A and SiMe 4 , and other saturated alkanes should be observed for mechanism B. For our experiments, the predominate Zr-alkyl species in solution is [(SBI)ZrCH 2 SiMe 3 ] ϩ because of the low levels of initiation, so a major byproduct of mechanism B should be SiMe 4 .…”

Section: Comparison Of B(c6f5)3 and [Cph3][b(c6f5)4] As Activators Formentioning

confidence: 99%

“…Benefits of single-site polymerization include access to a broader range of catalyst structures through rational syntheses, improved control of polymer molecular weight distributions, and compatibility with flexible solution-based polymerization processes. Perhaps more significantly, single-site catalysts enable the discovery and commercial production of novel polyolefin materials, such as ''blocky'' polymers, with unprecedented properties (2)(3)(4). From an academic viewpoint, homogeneous polymerization catalysts offer marvelous opportunities for probing reaction mechanisms and rational design that cannot be achieved with heterogeneous catalysts.…”

mentioning

confidence: 99%

“…Many of the initial discoveries of well defined single-site catalysts centered on metallocenes; however, the so-called nonmetallocenes account for many recent catalyst discoveries (5-7). The most active group 4 catalysts pair a cationic metal center with a noncoordinating anion, such as [MeB(C 6 F 5 ) 3 ] Ϫ , [B(C 6 F 5 ) 4 ] Ϫ , and the products of methide abstraction by methylalumoxane oligomers. Although methylalumoxane is widely used in industry, borane and trityl salt activators form isolable counteranions better suited for mechanistic studies.…”

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confidence: 99%

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Metallocene-catalyzed alkene polymerization and the observation of Zr-allyls

Landis

Christianson

2006

Proc. Natl. Acad. Sci. U.S.A.

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[where SBI is rac-Me 2Si(indenyl)2] with complete consumption of 1-hexene before the first NMR spectrum. Surprisingly, the first NMR spectrum reveals, aside from uninitiated catalyst, Zr-allyls as the sole catalyst-containing species. These Zr-allyls, which exist in two diastereomeric forms, have been characterized by physical and chemical methods. The mechanism of Zr-allyl formation was probed with a trapping experiment, leading us to favor a mechanism in which Zr-polymeryl undergoes ␤-H transfer to metal without dissociation of coordinated alkene followed by -bond metathesis to form H2 and Zr-allyl. Zr-allyl species undergo slow reactions with alkene but react rapidly with H2 to form hydrogenation products.dormant site ͉ mechanism ͉ metal allyl ͉ single-site O ver the past 20 years new catalyst technologies have reinvigorated polyolefin chemistry by rapidly expanding new polyolefin materials and technology. The so-called ''single-site'' catalysts based on homogeneous transition metal complexes form the leading edge of new catalyst technologies (1). Benefits of single-site polymerization include access to a broader range of catalyst structures through rational syntheses, improved control of polymer molecular weight distributions, and compatibility with flexible solution-based polymerization processes. Perhaps more significantly, single-site catalysts enable the discovery and commercial production of novel polyolefin materials, such as ''blocky'' polymers, with unprecedented properties (2-4). From an academic viewpoint, homogeneous polymerization catalysts offer marvelous opportunities for probing reaction mechanisms and rational design that cannot be achieved with heterogeneous catalysts.Catalysts based on group 4 metals (see examples in Fig. 1) exhibit the most attractive combination of activity, selectivity, and generality to a wide variety of ␣-olefins. Many of the initial discoveries of well defined single-site catalysts centered on metallocenes; however, the so-called nonmetallocenes account for many recent catalyst discoveries (5-7). The most active group 4 catalysts pair a cationic metal center with a noncoordinating anion, such as [MeB(C 6 F 5 ) 3 ] Ϫ , [B(C 6 F 5 ) 4 ] Ϫ , and the products of methide abstraction by methylalumoxane oligomers. Although methylalumoxane is widely used in industry, borane and trityl salt activators form isolable counteranions better suited for mechanistic studies.As with all polymerization reactions, the phases of chain growth include initiation, propagation, and termination (Fig. 2). The corresponding elementary rate laws and kinetic constants completely describe the catalytic kinetics and the distribution of polymer products (8). We have shown that a combination of active site counting methods, quenched flow reaction kinetics, and polymer end group analysis applied to 1-hexene polymerization catalyzed by B(C 6 F 5 ) 3 -activated catalyst, [(EBI)Zr(Me)][MeB(C 6 F 5 ) 3 ] [where EBI is rac-C 2 H 4 (indenyl) 2 ], lead to rigorous characterization of the kinetic rate laws (8-...

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“…communications. [1,2] These authors had already reported [3] that the (h 5 -pentamethylcyclopentadienyl)Zr-amidinate (Cp Ã )-{N( t Bu)C(Me)N(Et)}ZrMe 2 (Scheme 1, 1) can be converted by methide abstraction (e.g., with [HMe 2 N(C 6 …”

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confidence: 99%

Catalytic Olefin Polymerization is a Mature Field. Isn't it?

Busico

2007

Macro Chemistry & Physics

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In spite of the reputation to be a mature area, Ziegler‐Natta olefin polymerization continues to produce scientific and industrial breakthroughs at a surprising pace. The massive introduction of High Throughput Screening technologies has accelerated the innovation process even further. This Highlight aims at introducing the reader to a number of very recent publications in which novel metallocene and non‐metallocene (“post‐metallocene”) olefin polymerization catalysts, and new concepts of chain growth in insertion polymerization, are disclosed and elegantly and convincingly discussed.magnified image

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Discrete, Multiblock Isotactic–Atactic Stereoblock Polypropene Microstructures of Differing Block Architectures through Programmable Stereomodulated Living Ziegler–Natta Polymerization

Abstract: The past two decades have witnessed dramatic advances in the development of well-defined transition-metal complexes that can function as catalysts for the stereoselective Ziegler-

Cited by 137 publications

References 29 publications

Semicrystalline thermoplastic elastomeric polyolefins: Advances through catalyst development and macromolecular design

Semicrystalline thermoplastic elastomeric polyolefins: Advances through catalyst development and macromolecular design

Metallocene-catalyzed alkene polymerization and the observation of Zr-allyls

Catalytic Olefin Polymerization is a Mature Field. Isn't it?

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