Ethylene/propene copolymerization

In ethylene—propene copolymerization the former monomer is greatly favoured and a value for r, of 72 was found. Hydrogen is particularly active as a chain transfer agent for this catalyst, a value of fetr,H,/ tr,M 3.8 X 10 being quoted, some ten times greater than that for a conventional Ziegler system [133b]. The active species in both these systems was ascribed to a low valence Cr complex. 

A) Monomer feed and copolymer composition for ethylene/propene copolymerization with the catalyst VCl4/AlEt2Cl at —78°C have been shown to fit accurately empirical relationships [322]... 

Homogeneous vanadium-based catalysts formed by the reaction of vanadium compounds and reducing agents such as organoaluminum compounds [10-12] are used industrially for the production of elastomers by ethylene/propene copolymerization (EP rubber) and ethylene/propene/diene terpolymerization (EPDM rubber). The dienes are usually derivatives of cyclopentadiene such as ethylidene norbomene or dicyclopentadiene. Examples of catalysts are Structures 1-4. Third components such as anisole or halocarbons are used to prevent a decrease in catalyst activity with time which is observed in the simple systems. 

The copolymerization of carbonyl monomes with alkenes has been even less studied than that between different carbonhyl monomers. The radiation-initiated copolymerization of styrene with formaldehyde proceeds by a cationic mechanism with a trend toward ideal behavior, r = 52 and r2 = 0 at —78°C [Castille and Stannett, 1966]. Hexafluoroacetone undergoes radiation-initiated copolymerization with ethylene, propene, and other a-olefins [Watanabe et al., 1979]. Anionic copolymerizations of aldehydes with isocyanates have also been reported [Odian and Hiraoka, 1972]. 

Statistical copolymerization occurs among ethylene and various a-olefins [Baldwin and Ver Strate, 1972 Cooper, 1976 Pasquon et al., 1967 Randall, 1978]. The reactivities of monomers in copolymerization generally parallel their homopolymerization behavior ethylene > propene > 1-butene > 1-hexene [Soga et al., 1989]. Table 8-7 shows monomer reactivity ratios for several comonomer pairs. 

The uncertainties and poor j eement in determinations of ethylene/ propene reactivity ratios from monomer and polymer composition [m = (Mj/Mj) monomer p = (Mi/M2) polymer] and the copolymerization equation p = (1 + rjm)/(l + rj/m) give particular interest to approaches based on the analysis of monomer unit distributions in the copolymer. 

Two classes of diene have been copolymerized successfully with ethylene/propene, in both of which one double bond is deactivated such that the monomer behaves as a mono-olefin. These are unconjugated diolefins, such as cis and trans 1,4-hexadiene or 3,7-dimethyl 1,6-octa-diene, and compounds containing the 2-norbornene structure... 

The copolymerization of ethylene and carbon monoxide to give alternating copolymers has attracted considerable interest in both academia and industry over recent decades [1, 2]. Attention was focused on aliphatic polyketones such as poly(3-oxotrimethylene) (1) because of the low cost and plentiful availability of the simple monomers. The new family of thermoplastic, perfectly alternating olefin/ carbon monoxide polymers commercialized by Shell provides a superior balance of performance properties not found in other commercial materials the an ethylene/ propene/CO terpolymer is marketed by Shell imder the tradename Carilon . About the history of polyketones see Refs. [3-11],... 

Coordination copolymerization of ethylene with small amounts of an a-olefin such as 1-butene, 1-hexene, or 1-octene results in the equivalent of the branched, low-density polyethylene produced by radical polymerization. The polyethylene, referred to as linear low-density polyethylene (LLDPE), has controlled amounts of ethyl, n-butyl, and n-hexyl branches, respectively. Copolymerization with propene, 4-methyl-1-pentene, and cycloalk-enes is also practiced. There was little effort to commercialize linear low-density polyethylene (LLDPE) until 1978, when gas-phase technology made the economics of the process very competitive with the high-pressure radical polymerization process [James, 1986]. The expansion of this technology was rapid. The utility of the LLDPE process Emits the need to build new high-pressure plants. New capacity for LDPE has usually involved new plants for the low-pressure gas-phase process, which allows the production of HDPE and LLDPE as well as polypropene. The production of LLDPE in the United States in 2001 was about 8 billion pounds, the same as the production of LDPE. Overall, HDPE and LLDPE, produced by coordination polymerization, comprise two-thirds of all polyethylenes. 

Figure 5 Productivity in the copolymerization of ethylene with 1-propene, 1-hexene or 1,5-hexadiene...

The highest productivity of 4400 kg polymer/g Zr resulted in the homopolymerization of ethylene. It was found lower in the copolymerization with propene, 1-hexene and 1,5-hexadiene. With increasing concentration of the comonomer in the feed the productivity decreased and was only 50 to 600 kg polymer/g Zr in the homopolymerization of the pure comonomers. The lowest productivity was observed with 1,5-hexadiene. 

The product of hydrogenation of natural rubber is atactic. This product also results from the radical copolymerization of propene with ethylene. 

An interesting effect is observed for the polymerization with ethylene(bisin-denyl) zirconium dichloride and some other metallocenes (Fig. 5). Although the activity of the homopolymerization of ethene is very high, it increases when copolymerizing with propene [66]. 

Uncomplexed acrylates do not copolymerize with ethylene only polyacryla-les (e.g. polyethyl acrylate) are formed. BF2 is a strong Lewis acid used as an initiator in cationic polymerizations. With acrylic monomers it forms a complex which can be relatively easily copolymerized with ethylene and propene. This process is similar to radical reactions it requires an initiator [96],... 

There exist many alternating copolymerizations ethylene or propene with alkyl acrylates [244], vinyl acetate with maleic anhydride [245], styrene with acrylonitrile [246], styrene with fumaronitrile [247], vinyl carbazol with fumaronitrile, vinyl ferrocenne with diethylfumarate [248], and further pairs or systems of three monomers [238, 249-253]. External conditions can support or hinder alternation. At not too high temperatures, vinyl acetate forms a donor—acceptor complex with maleic anhydride. Under these conditions (and in the presence of a radical initiator), an alternating copolymer is formed. The concentration of the complex decreases with increasing temperature above 363 K the complex cannot exist. Under these conditions, copolymerization yields a statistical copolymer whose composition depends on the composition of the monomer mixture [245]. 

The dimerization of propene in a flow system over supported potassium or sodium on graphite or potassium carbonate, at 150° and under pressure, gave good yields of dimers, and the copolymerization of ethylene with propene on supported alkali metal catalysts gave 92 pentenes (9). 

With the VCl4/Al(Hex)3 catalyst the ratio of the rates of polymerization of ethylene and propene is ca. 1800, considerably larger than that found for more active catalysts for propene polymerization, such as TiCl4 /AIR3. The lai e ratio for the vanadium catalysts is because most of the catalyst sites cannot initiate the polymerization of propene, although once they have added a molecule of ethylene they can subsequently add either ethylene or propene. In conformity with this view it is found that the soluble portion of the catalyst will polymerize ethylene but not propene. The overall activation energy for copolymerization with VCI4 /Al(Hex)3 was found to be 6.5 kcal mole and to be the same as for the two individual monomers [194]. 

Ethylene copolymerization Random comonomer distribution, LLDPE comonomers propene, higher a-olefins, cycloolefins (COC), dienes... 

It is also possible to copolymerize ethylene with a-olefins such as propene, 1-butene, 1-pentene, 1-hexene, and 1-octene, forming linear low-density polyethylene (LLDPE). The product of copolymerization parameters V2 obtained by using ethylenebis(l-indenyl)zirconium dichloride (11) indicates random incorporation of the comonomer [38]. 

Most unsaturated substances such as alkenes, alkynes, aldehydes, acrylonitrile, epoxides, isocyanates, etc., can be converted into polymeric materials of some sort—either very high polymers, or low-molecular-weight polymers, or oligomers such as linear or cyclic dimers, trimers, etc. In addition, copolymerization of several components, e.g., styrene-butadiene-dicyclo-pentadiene, is very important in the synthesis of rubbers. Not all such polymerizations, of course, require transition-metal catalysts and we consider here only a few examples that do. The most important is Ziegler-Natta polymerization of ethylene and propene. 

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