Olefin polymerization, titanium based

Transition metal catalysis plays a key role in the polyolefin industry. The discovery by Ziegler and Natta of the coordination polymerization of ethylene, propylene, and other non-polar a-olefins using titanium-based catalysts, revolutionized the industry. These catalysts, along with titanium- and zirconium-based metallocene systems and aluminum cocatalysts, are still the workhorse in the manufacture of commodity polyolefin materials such as polyethylene and polypropylene [3-6],... 

The formation of high polymers of olefins in the presence of titanium halogenides with no specially added organometallic co-catalysts was discovered long ago [see (147), and the references therein], A complete description of various alkyl-free polymerization catalysts based on the use of transition metal chlorides may be found in the review by Boor (17), where a comparison of these catalysts with traditional two-component systems is given. 

Ethylene is conveniently polymerized in the laboratory at atmospheric pressure using a titanium-based coordination catalyst [34]. It may also be polymerized less conveniently in the laboratory under high pressures using free radical catalysts at high and low temperatures [35-37]. Other olefins such as propylene, 1-butene, or 1-pentene homopolymerize free radically only to low molecular weight polymers and require ionic or coordination catalysts to afford high molecu-... 

Work on organometal initiator systems for solution polymerization increased significantly with the discovery of the titanium based initiators for olefin polymerization by Karl Ziegler. 

Values in the literature relate to olefin polymerization with heterogeneous titanium based catalysts where the necessary information has been acquired, and the data are given in Table 9. It would not appear to... 

Metallocene derivatives are the most extensively studied class of homogeneous catalysts for the polymerization of olefins. Less saturated and less hindered mono-Gp group 4 metal species of the type [Cp MR2]+ (Cp denotes Cp or a substituted cyclopentadienyl ring) may also behave as useful catalysts or initiators for olefin polymerization. Catalysts for syndiospecific polymerization of styrene based on mono-Cp titanium derivatives with different substituents on the Gp ligand and with various types of tetraphenylborates have been examined. A good relationship between the... 

Recent progresses in the development of the titanium-phosphinimido complexes and their application as olefin polymerization pre-catalysts have been reviewed - and related computational studies have been reported. Based on these theoretical results, the synthesis of a family of pre-catalysts of general formula Cp TiX2[NP(NR2)3] (X = C1, Me) (Scheme 234) containing the tris(amino)phosphinimido ligand has been described.638... 

Silver- and titanium-based nanoparticles are ideal for incorporation into membranes, to reduce the biofouling of polymeric membranes. Silver nanoparticles are also involved in facilitating olefin fransporfafion in fhe gas separation fechniques... 

Many ot-olefins were polymerized by the Ziegler-Natta catalysts to yield high polymers and many such polymers were found to be stereospecific and crystalline. Polymerizations of a-olefins of the general structure of CH2 = CH — (CH2) — R, where x is 0-3 and R denotes CH3, CH-(CH3)2, C(CH3)3, or CsHs, can be catalyzed by vanadium trichloride/triethyl aluminum [80]. The conversions are fairly high, though higher crystallinity can be obtained with titanium-based catalysts [81]. Addition of Lewis bases, such as ( 4119)20, (C4H9)3N, or ( 4119)3 , to the catalyst system further increases crystallinity [82]. 

Recently, Baird and co-workers have reported (75) examples of polymerizations by a simple mono-Cp titanium complex, (C5(CH3)5)Ti(CH3)3 activated with a Lewis acid (B(C6F5)3) that not only copolymerizes ethylene and a-olefins but also induces polymerization of monomers normally associated with cationic polymerization such as isobutylene and vinyl ethers. Shaffer and Ashbaugh foimd (76) that for isobutylene and a-methylstyrene, the metal complex is an initiator rather than a catalyst (if it even participates at all), but that a transition from cationic to coordination polymerization occurs in styrene polymerization as temperature is raised. Even if it merely functions as an initiator, however, these investigations have revealed new polymerization systems based on anions such as [RB(C6F5)3l (R = alkyl, CeFs) that are less prone to side reactions tending to limit the MW and degree of polymerization of monomers like isobutylene at moderate temperatures (T > -80°C). 

Monocyclopentadienyl and (monoindenyl)titanium trichlorides are generating interest as catalyst precursors for syndiospecific polymerization of styrene (112-127). A class of highly active olefin pol5unerization catalysts based on a (monocyclopentadienyl)titanium dimethyl cation [CpTi(CH3)2l+, generated hy... 

A variety of Group 4 metal complexes, in combination with common olefin polymerization activators, have been evaluated as potential catalysts for syn-diospecific polymerization of styrene (for reviews, see Refs. 114, 115, 123, and 426). Monocyclopentadienyl and monoindenyl titanocenes generally exhibit the highest activities (eq. 5) (112-127). Curiously, half-sandwich titanium-trifluoride-based catalysts are more active than their trichloride analogues (124,427,428). The polymerization mechanism for sPS formation is under debate. Kinetic studies and spectroscopic investigations of the catalytic systems suggest a cationic Ti(III) complex as the active species (123). 

Takaoki, K. Miyatake, T. Titanium and vanadium based non-metaUocene catalysts for olefin polymerization. Macromol. Symp. 2000,157, 251-257. 

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