Coordination polymerization metallocene

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 annual production of various polymers can be measured only in billion tons of which polyolefins alone figure around 100 million tons per year. In addition to radical and ionic polymerization, a large part of this huge amount is manufactured by coordination polymerization technology. The most important Ziegler-Natta, chromium- and metallocene-based catalysts, however, contain early transition metals which are too oxophiUc to be used in aqueous media. Nevertheless, with the late transition metals there is some room for coordination polymerization in aqueous systems [1,2] and the number of studies published on this topic is steadily growing. 

Coordination Polymerization of 1,3-Dienes Single-Site (or Metallocene) Catalysts Living Radical Polymerizations Other Types of Polymerizations, Polymers Ring-Opening Polymerization... 

However, there is also a major difference between the two types of catalysts. The olefin polymerization metallocene catalysts (cf. Section 2.3.1.1) are much more electrophilic, due to the higher positive charge of the metal ion, than the pal-ladium(II) complexes discussed above. For polyketone formation, electrophilicity needs to be balanced so that olefins can still compete with carbon monoxide for coordination to the metal cation. 

Not only palladium, but many more non-metallocene late (and early) transition metal catalysts for the coordination polymerization of ethene and 1-olefins were reported [11]. Among the most significant findings in this area are the disclosures of novel highly active and versatile catalysts based on (i) bidentate diimine [N,N] nickel and palladium complexes [12], (ii) tridentate 2,6-bis(imino)pyridyl [N,N,N] iron and cobalt complexes [13], and (iii) bidentate salicyl imine [N,O] nickel complexes [14]. 

An interesting example of the reaction mechanisms with multiple cycles is coordination polymerization. The most important industrial coordination polymerization processes are Ziegler-Natta and metallocene catalyzed olefin polymerization processes (Figure 5.31). 

Coordination polymerization involves the use of transition metal catalysts. Examples are Ziegler-Natta polymerization by Tl/Al systems, metallocene polymerization with Ti, Zr, Hf catalysts, or metathesis polymerization with W, Mo, Re metals. Synthesis of functional polymers by organometallic catalysts are particularly difficult because transition metds are not only l ed by protic functionality, they are often poisoned by heteroatoms (e.g. N, O). 

Coordination polymerization of hydroxyl, carboxyl and amino monomers can also be effected by the judicious use of protecting groups. For example, amino and hydroxyl monomers have been protected by silyl ethers and aluminate salts for Ziegler Natta and/or metallocene polynrierization and carboxyl monomers have been protected via aluminate salts. Alternatively, organoborane synthons have been used to carry... 

A great variety of possibilities are available when a metal is part of a linear or crosslinked macromolecule (Section 1.2.1, Fig. 7-1). One possibility is the covalent incorporation of a metal into a homochain (metal-metal connections) or a heterochain (metal-heteroatom connections). Coordinative bonds between a metal ion and another coordinating donor group can lead to linear chains or to supramolecular organizations when coordination polymers are formed. n-Bonds between rt-rich aromatic compounds and metal ions can result in polymeric metallocenes. Covalent and coordinative bonds are realized in cofacially stacked metal complexes. In addition, dendrimers containing the interaction of metals and another group in different bonds are treated in this chapter. 

Fig. 5 Cationic group 4 metallocene catalysts employed for investigation of coordination polymerization of MBL, yMMBL, and MMBL...

In a recent study, Yu et al. combined the palladium-diimine-catalyzed metallocene polymerization and ATRP to synthesize polyethylene-h-polystyrene and polyethylene-h-poly(butyl acrylate) [165]. A relatively new coordination olefin polymerization method - degenerative transfer coordination polymerization - was recently combined with ATRP to prepare block and graft copolymers with linear polyethylene segments [166-169]. 

Metallocenes or late transition metal catalysts were iiKxeas-ingly utilized over the years for the (co)polymetization of olefins including the synthesis of graft copolymers. In this last case coordination polymerization had to be combined with other polymerization processes to give access to macromonomets. However, only a few examples of coordination homopolymer-ization or copolymerization of macromonomets aimed to design comb-shaped polymers were described in the literature. In the following these examples will be described briefly. 

These linear elastomers are produced by coordination polymerization using a Phillips or Z-N catalyst at low P and T. Here belongs Mxsten XLDPE from Eastman Chem. and Attane ULDPE from Dow. The first metallocene-catalyzed VLDPE was a hexene copolymer with p = 0.912 g mL made in the UNIPOL gas-phase process with Z-N catalyst and introduced by ExxonMobil as Exceed metallocene VLDPE. The resin has outstanding sealing properties (hot tack and seal strength) compared with ZN-VLDPE. The solution polymerization in a hydrocarbon usually is carried out in a continuously stirred tank reactor (CSTR), at r = 160-300 °C and P = 2.5-10 MPa with the residence time of 1-5 min [Dow in 1992 and UCC in... 

In chain reactions the different types of monomers can be added subsequently to an active chain end. The most important techniques here are sequential living polymerization techniques, such as anionic or cationic polymerization. Certain metallocenes can be used in coordination polymerization of olefins leading to stereo block copolymers, like polypropylene where crystalline and amorphous blocks alternate with each other due to the change of tacticity along the chain [34]. In comparison to living polymerization techniques, free radical and coordination polymerization lead to rather polydisperse materials in terms of the number of blocks and their degree of polymerization. 

The coordination polymerization by transition-metal catalysts, such as Ziegler—Natta catalysts or metallocenes, is the most versatile method for preparing Unear polyolefins under mild and controlled conditions. Unfortunately, attempts at direct incorporation of functional monomers during polymerization run into the problem of catalyst poisoning caused by the interaction of organic functimialities with the catalyst center [129]. 

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