Ziegler-Natta catalysts styrenes

Olig omerization and Polymerization. Siace an aHyl radical is stable, linear a-olefins are not readily polymerized by free-radical processes such as those employed ia the polymerization of styrene. However, ia the presence of Ziegler-Natta catalysts, these a-olefins can be smoothly converted to copolymers of various descriptions. Addition of higher olefins during polymerization of ethylene is commonly practiced to yield finished polymers with improved physical characteristics. 

Metallocene catalysis can also make possible the production of copolymers of propylenes with monomers such as long-chain olefins, cyclic olefins and styrene which is not possible with more conventional Ziegler-Natta catalysts. 

Attempts to produce coplymers of ethylene and styrene by free radical and by conventional Ziegler-Natta catalysts systems have, over the years, not proved successful. However, in 1998 Dow announced novel polymers using a metallocene process with the intention of commercial polymerisation using a 23 000t.p.a. capacity plant starting in 1999. 

Hivalloy A process for grafting styrenic polymers on to polyolefines, using a Ziegler-Natta catalyst. The products combine the physical properties of both polymer types. Developed by Montell and commercialized in the United States in 1997. See also Catalloy. Oxley, D. F., Chem. Ind. (London), 1998, (8), 307. 

Stereospedfic Polymerization of Styrene with Ziegler-Natta-Catalysts... 

PS PSF PSU PTFE PU PUR PVA PVAL PVB PVC PVCA PVDA PVDC PVDF PVF PVOH SAN SB SBC SBR SMA SMC TA TDI TEFE TPA UF ULDPE UP UR VLDPE ZNC Polystyrene Polysulfone (also PSU) Polysulfone (also PSF) Polytetrafluoroethylene Polyurethane Polyurethane Poly(vinyl acetate) Poly(vinyl alcohol) poly(vinyl butyrate) Poly(vinyl chloride) Poly(vinyl chloride-acetate) Poly(vinylidene acetate) Poly(vinylidene chloride) Poly(vinylidene fluoride) Poly(vinyl fluoride) Poly(vinyl alcohol) Styrene-acrylonitrile copolymer Styrene-butadiene copolymer Styrene block copolymer Styrene butadiene rubber Styrene-maleic anhydride (also SMC) Styrene-maleic anhydride (also SMA) Terephthalic acid (also TPA) Toluene diisocyanate Ethylene-tetrafluoroethylene copolymer Terephthalic acid (also TA) Urea formaldehyde Ultralow-density polyethylene Unsaturated polyester resin Urethane Very low-density polyethylene Ziegler-Natta catalyst... 

It may be of interest that isotactic polystyrene formed by styrene polymerisation with Ziegler Natta catalysts [13] did not appear to be a polymer that could exhibit significantly better usable properties compared with atactic polystyrene produced in free radical styrene polymerisation processes. 

Subsequent investigations revealed that, in principle, styrene undergoes isospecific polymerisation in the presence of heterogeneous Ziegler Natta catalysts [1-4], Although polystyrene of isotactic structure was also prepared with the use of homogeneous nickel-based coordination catalysts, it appeared to be of low molecular weight [22,23]. 

Although the isospecific polymerisation of styrene monomers has much less steric demands for the Ziegler-Natta catalysts than that of x-oldins, it proceeds with much lower propagation rate constants by comparison with the polymerisation of x-olefins for example, on a molar basis, styrene is ca 100 times less reactive than propylene in the polymerisation [30,33], Also, compare the relatively slow polymerisation of styrene and other vinylaromatic monomers with the relatively fast polymerisation of vinylcyclohexane [20,31,34-36]. 

The mechanism of the isospecific polymerisation of styrene and its ring-substituted analogues in the presence of heterogeneous Ziegler-Natta catalysts is the same as for x-olefins. As regards the mode of monomer insertion, it has been reported as primary (1,2) insertion [37,38]. 

Styrene polymerisation with heterogeneous Ziegler Natta catalysts activated by alkylaluminium compounds generally produces a mixture of isotactic and non-stereoregular polymer. For example, polystyrene produced with the... 

One of the best catalysts for the syndiospecific polymerisation of styrene appeared to be that derived from CpTiCl3 and methylaluminoxane. The polymerisation rate for this system decreases with increasing polymerisation time such behaviour is very similar to that of other Ziegler Natta catalysts. A maximum polymerisation rate is achieved at 50 °C [6]. Other catalysts such as CpTi(OBu)3 [Al/Me/O] are also reported to exhibit a very high activity and syndiospecificity in the polymerisation of styrene [50,51]. 

Styrene, which can be treated formally as an a-olefin branched in the 3-position, forms copolymers with ethylene and a-olefins (as well as with /i-olefins, involving isomerisation copolymerisation). Both heterogeneous Ziegler-Natta catalysts and a single-site metallocene catalyst promote the copolymerisation. 

Styrene undergoes copolymerisation with ethylene and various a-olefins in the presence of heterogeneous Ziegler-Natta catalysts. Its reactivity in the copolymerisation is quite low, which is illustrated by the values of the relative reactivity ratios, r and r2, presented in Table 4.5 [118]. One may note, however, a considerably high relative reactivity of styrene in copolymerisation with vinyl-cyclohexane. The copolymerisation of styrene with small amounts of a-olefin, such as 1-octene or 1-decene, yields copolymers of reduced crystallinity and thus reduced brittleness compared with the homopolymer of styrene. 

Styrene/a-olefin copolymers containing a predominant amount of styrene units can be easily formed through the monomer isomerisation-copolymerisation of styrene and /i-olefin such as m-2-butene in the presence of heterogeneous Ziegler-Natta catalysts such as TiCl3—AlEt3. Styrene appeared to be a favourable comonomer for monomer isomerisation-copolymerisation with internal olefins, since only the isomerisation of /i-olefin to a-olefin, and not the isomerisation of styrene (in contrast to the olefin), occurs in the presence of Ziegler Natta catalysts [119] ... 

Table 4.5 Relative reactivity ratios for copolymerisation of styrene (ri) and a-olefins (r2) with heterogeneous Ziegler-Natta catalysts...

How can one obtain styrene-rich styrene/ot-olefin copolymers using heterogeneous Ziegler-Natta catalysts Give an example. 

What are the advantages of half-sandwich metallocene-based catalysts as compared with heterogeneous Ziegler-Natta catalysts in styrene polymerisation What are the possible consequences of this for developing industrial processes ... 

Beside the homopolymerization of BD Nd-based Ziegler/Natta catalyst systems are also applied for the homopolymerization of IP, the copolymerization of the dienes BD and IP, the homopolymerization and copolymerization of substituted dienes as well as for the copolymerization of BD with alkenes such as styrene, ethylene and other ethylene derivatives. 

The Ziegler-Natta catalyst trimethylammonium o-methyl-1-(2-hydroxy Icy do hexyl)-carborane zirconium chloride has been prepared and affixed to a Merrifield resin. When used as a polymerization catalyst for vinyl chloride, t-butyl acrylate, styrene, or ethylene, oligomers with molecular weights <6000 daltons were obtained. 

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