One of the most exciting developments in the areas of catalysis, organometallic chemistry, and polymer science in recent years has been the intense exploration and commercialization of new polymerization technologies based on single-site and metallocene coordination olefin polymerization catalysts.1 The vast number of specifically designed/synthesized transition metal complexes (catalyst precursors) and main-group organometallic compounds (cocatalysts) allows unprecedented control over polymer microstructure, the generation of new polymer architectures, and the development of new polymerization reactions. Commercialization of new generations of single-site and metallocene catalyst-based technologies has provided the multibillion pound per year polyolefins industry with the ability to deliver a wide range of new and innovative olefin-based polymers having improved properties.2-4 The intense industrial activity in the field and the challenges to our basic understanding that have come to light have in turn 1391 Chem. Rev. 2000, 100, 1391−1434

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Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure−Activity Relationships

Precise control of polyolefin stereochemistry using single-site metal catalysts.

Stereoselective Ring-Opening Polymerization of meso-Lactide: Synthesis of Syndiotactic Poly(lactic acid)

Research on "post-metallocene" polymerization catalysis ranges methodologically from fundamental mechanistic studies of polymerization reactions over catalyst design to material properties of the polyolefins prepared. A common goal of these studies is the creation of practically useful new polyolefin materials or polymerization processes. This Review gives a comprehensive overview of post-metallocene polymerization catalysts that have been put into practice. The decisive properties for this success of a given catalyst structure are delineated.

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Post-metallocenes in the industrial production of polyolefins.

On treatment with 1 equiv of [Ph3C][B(C6F5)4], the scandium half-sandwich bis(alkyl) complex (C5Me4SiMe3)Sc(CH2SiMe3)2(THF) showed extremely high activity (up to 1.36 × 104 kg of sPS/(mol Sc·h)) and syndiospecificity (rrrr > 99%) for the polymerization of styrene at room temperature in toluene. More remarkably, this catalyst system could also effect the syndiospecific copolymerization of styrene with ethylene to yield styrene−ethylene copolymers having syndiotactic styrene−styrene sequences. The styrene content in the copolymers could be easily controlled by changing the styrene feed and could reach higher than 80 mol %. This is the first example of formation of such types of styrene−ethylene copolymers, which are expected to show novel properties.

Scandium half-metallocene-catalyzed syndiospecific styrene polymerization and styrene-ethylene copolymerization: Unprecedented incorporation of syndiotactic styrene-styrene sequences in styrene-ethylene copolymers

Syndiotactic polystyrene, namely XAREC® is being developed by Idemitsu Petrochemical Co., Ltd. as a major new polymer family. XAREC® is a new crystalline engineering thermoplastic with a crystalline melting point of 270 °C. Because of its crystalline nature, XAREC® has a high heat resistance, an excellent chemical resistance and a water/steam resistance. XAREC® also has the dip soldering resistance. Potential applications for XAREC® include surface-mount electronic devices and electrical connectors. In this paper, some mechanistic models for polymerization and stereo-regulation as well as the factors which affect the activity and stereospecificity of the catalysts are discussed. The effects of substitutions on Cp ligand of half titanocene complexes were examined. The bulky substitution groups reduce the activity. Also, borate compounds as activator and effects of hydrogen are discussed.

Syndiospecific polymerization of styrene

Several non-metallocene (Ti, Zr) and substituted mono-Cp titanium metallocenes have been tested in the presence of methylalumoxane (MAO) as catalyst for syndiospecific polymerization of styrene. Effect of substitutions on the titanium and Cp ligand, molar ratio of Al/Ti, TMA and temperature on activity, Mwt. and % sPS were studied. CpTi(OiPr)3 gives a less active catalyst than Cp*Ti(OiPr)3 and the resulting sPS is less stereoregular and of lower molecular weight.

Mao based catalysts for syndiotactic polystyrene (sPS)

There are disclosed carbonate polymers having terminal arylcyclobutene moieties. Such carbonate polymers are prepared from one or more multi-hydric compounds and have an average degree of polymerization of at least about 2 based on multi-hydric compound. These polymers, including blends thereof, can be easily processed and shaped into various forms and structures according to the known techniques. During or subsequent to the processing, the polymers can be crosslinked, by exposure to heat or radiation, for example, to provide crosslinked polymer compositions. These compositions have a good combination of properties, including for example, processability into shaped articles having unexpectedly good combinations of toughness, solvent resistance, ignition resistance, modulus and resistance to thermal linear expansion.

Arylcyclobutene terminated carbonate polymer

Vinyl aromatic polymers having stereo regular structure of high syndiotacticity are prepared utilizing coordination catalysts in a suspension polymerization process.

Suspension polymerization of vinyl aromatic monomers to polymer having high syndiotacticity

The syndiotactic polystyrene polymerization activity of a fluorinated half-sandwich complex, η 6 -pentamethylcyclopentadienyl titanium trifluoride (Cp * TiF 3 ), in the presence of relatively low amounts of methylalumoxane (MAO; MAO/Cp * TiF 3 molar ratio = 200/1) and triisobutylaluminum, is significantly increased by the addition of phenylsilane in molar ratios to Cp * TiF 3 ranging from about 300/1 to 600/1, if the phenylsilane is added to the monomer. Lower amounts of phenylsilane, such as a 100/1 molar ratio to Cp * TiF 3 , lead to a reduced polymerization activity in comparison with styrene without phenylsilane. A prereaction of phenylsilane with the catalyst mixture shows a behavior that is strongly dependent on the storage time of the composition and the temperature. A storage time of about 16 h is sufficient to reduce the polymerization conversion to about half of the original value. The results are discussed on the basis of a chain-transfer reaction with phenylsilane and several catalyst complexes of different stabilities and activities, including an alkylation product of phenylsilane.

Thomas H. Newman

Papers

Syndiospecific polymerization of styrene

Mao based catalysts for syndiotactic polystyrene (sPS)

Arylcyclobutene terminated carbonate polymer

Suspension polymerization of vinyl aromatic monomers to polymer having high syndiotacticity

The influence of phenylsilane on the syndiotactic polymerization of styrene with ?5-pentamethylcyclopentadienyl titanium trifluoride