Ethylene and propylene copolymerization

Ethylene-propylene rubbers are the important class of elastomers and are widely used in many branches of industry due to their unique properties, in particular good stability to environmental effects, good physical-chemical and elastic characteristics, chemical and ozone-stability, radiation, oils, acids and alkalis stability, etc. [78,79,176,207,253]. 

Triple ethylene-propylene rubbers of SKEP(T) brands contain up to several percents of non-conjugated dienes predominantly dicyclopentadiene (DCPD) and ethylidennorbomene (ENB) as third comonomers [177]. 

At the first time ethylene and propylene copolymers were put into industrial production in 1959 in Italy due to Ziegler-Natta catalytic systems discovery [176,177]. At present various SKEP(T) types are produced in all leading in industry countries particularly in USA, Italy, Germany, Holland, Great Britain, Canada, Japan, France, etc. Nevertheless, there is a lack of ethylene-propylene rubbers at world markets at present and this fact determines advisability of their production expansion. 

In Russia the first and the only large production of SKEP(T) in high-boliling hydrocarbons medium (hexane, heptane, etc.) was placed in operation on zavod SK OAO 

Among known Ziegler-Natta catalytic systems catalysts on the base of V and Ti compounds combination with chloroaluminumalkyles are effective for ethylene and propylene copolymerization [176, 177]. It is particularly convenient to use systems on the base of vanadium compounds (tetrachloride, trichloroxide, triacetylacetonate) and diisobutylaluminum chloride. 

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Ethylene—Propylene Rubber. Ethylene and propylene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) rubber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional rubbers such as SBR and PBD. Ethylene—propylene rubber (EPR) requires peroxide vulcanization. 

Vanadium(IV) forms complexes with charged carboxylate, aryloxide and alkoxide functionalities as well as the neutral carbonyl group. The steric crowding of the /-butoxides allowed structural characterization of the tetraalkoxide (96) by gas-phase electron diffraction.475 Vw phenoxide complexes derived from ligands such as 2-(dimethylaminomethyl)phenol and 4-chloro-2-[(dimethylamino)methyl]phenol are active as ethylene and propylene copolymerization agents 476 Complexes with silanoxides have been prepared by the oxidation of Vnl complexes.477... 

Figure 6.4. Tubular turbulent apparatus for formation of homogeneous high-dispersed sites of macromolecules propagation under ethylene and propylene copolymerization.

Formation of active sited in turbulent regime under ethylene and propylene copolymerization initi-... 

Single-site catalysts enable a broader range of altemalive comOTumers in ethylene and propylene copolymerizations through better comonomer respraise, which allows the use of much lower polar comonomer concentrations. Dramatically new technical properties could be achieved in polyolefin materials when the properties of polyolefins and polar comonomers were combined [16-18]. 

Boron Bromide. Approximately 30% of BBr produced in the United States is consumed in the manufacture of proprietory pharmaceuticals (qv) (7). BBr is used in the manufacture of isotopicaHy enriched crystalline boron, as a Etiedel-Crafts catalyst in various polymerization, alkylation, and acylation reactions, and in semiconductor doping and etching. Examples of use of BBr as a catalyst include copolymerization of butadiene with olefins (112) polymerization of ethylene and propylene (113), and A/-vinylcarbazole (114) in hydroboration reactions and in tritium labeling of steroids and aryl rings (5). 

Table 2 shows characteristic reactivity ratios for selected free-radical, ionic, and coordination copolymerizations. The reactivity ratios predict only tendencies some copolymerization, and hence some modification of physical properties, can occur even if and/or T2 are somewhat unfavorable. For example, despite their dissimilar reactivity ratios, ethylene and propylene can be copolymerized to a useful elastomeric product by adjusting the monomer feed or by usiag a catalyst that iacreases the reactivity of propylene relative to ethylene. 

A copolymer, on the other hand, results from two different monomers hy addition polymerization. For example, a thermoplastic polymer with better properties than an ethylene homopolymer comes from copolymerizing ethylene and propylene ... 

Random copolymers made by copolymerizing equal amounts of ethylene and propylene are highly amorphous, and they have rubbery properties. 

Although hdpe and it-PP are crystalline, the commercial random copolymer of ethylene and propylene (EP) is an amorphous elastomer. The most widely used EP copolymer (EPDM) is produced by the copolymerization of ethylene and propylene with a small amount of an alkyldiene this permits cross-linking or vulcanization. 

With larger amount of propylene a random copolymer known as ethylene-propylene-monomer (EPM) copolymer is formed, which is a useful elastomer with easy processability and improved optical properties.208,449 Copolymerization of ethylene and propylene with a nonconjugated diene [EPDM or ethylene-propylene-diene-monomer copolymer] introduces unsaturation into the polymer structure, allowing the further improvement of physical properties by crosslinking (sulfur vulcanization) 443,450 Only three dienes are employed commercially in EPDM manufacture dicyclopentadiene, 1,4-hexadiene, and the most extensively used 5-ethylidene-2-norbomene. 

The effect of nucleophilic dienes on the copolymerization of ethylene and propylene has been reported by Gladding, Fisher and Collette (88). Table 8 shows that 1.4-hexadiene decreased the tendency for propylene to enter into the ethylene-propylene terpolymer, produced by a triisobutyl aluminum-vanadium oxychloride catalyst. 

All higher a-olefins, in the presence of Ziegler-Natta catalysts, can easily copolymerize both with other a-olefins and with ethylene. In these reactions, higher a-olcfins arc all less reactive than ethylene and propylene. 

Leclerc and Waymouth (119) and, independently, Arndt et al. (120) synthesized alternating copolymers of ethylene and propylene with zirconocene catalysts. The ethylene/propylene (EP) copolymerizations were carried out at 30 and 60°C for each of four metallocene catalysts (Me2C(3-RCp)(Flu)) ZrCl2 (R = H, Me, lsoPr, tertBu) (Fig. 10). As the size of the substituent increased, there were distinct changes in the copolymerization behavior and in the polymer microstructure. 

Johnson LK, Mecking S, Brookhart M, Copolymerization of Ethylene and Propylene with Functionalized Vinyl Monomers by Palladium(II) Catalysts, J Am Chem Soc, 118, 267-268 (1996)... 

In the present paper we pay special attention to block polymers with polypropylene and polyethylene as the initial anionic block. However, both crystalline and amorphous block polymers of ethylene and propylene, butadiene, and several other olefins and dienes have been made by the AFR technique. The second or free radical block has been made from 4-vinylpyridine, 2-methyl-5-vinylpyridine, and mixtures with other monomers, as well as a number of acrylic monomers. Vinyl chloride, vinylidine chloride, vinyl acetate, and several related monomers have not been successfully copolymerized. 

Toughened polypropylene may be prepared by block copolymerization in which ethylene monomer is added during the final stages of the polymerization of propylene (4). Thus, some polypropylene chains would contain an end block of rubbery ethylene-propylene copolymer. Alternatively, a blend of an elastomeric copolymer of ethylene and propylene (EPR or EPDM) with isotactic polypropylene (PP) can produce an impact-resistant polymer (5). 

The same model has been used lt6) to explain the copolymerization of ethylene and propylene with TiCl+/EB/MgCl2—AlEt3, with various amounts of EB added to the cocatalyst. The triad sequence distribution calculated for the copolymer obtained without EB was in disagreement with reactivity ratios, while the values obtained with high concentrations of EB did agree. Thus, the two active species mentioned, having two and one vacancies respectively, would be characterized by... 

Unconjugated dienes can produce an even more complicated range of macro-molecular structures. Homopolymers of such monomers are not of current commercial importance but small proportions of monomers like 1,5-cyclooctadicne are copolymerized with ethylene and propylene to produce so-called EPDM rubbers. Only one of the diene double bonds is enchained when this terpolymeriza-tion is carried out with Ziegler-Natta catalysts (Section 9.5). The resulting small amount of unsaturation permits the use of sulfur vulcanization, as described in Section 1.3.3. 

The copolymerization of ethylene and propylene is found to be essentially random r ri = 1) with (C2H5)2AICI/VO(OC2H5)3 catalyst in chlorobenzene at 30°C. (Such polymerizations are discussed in Chapter 9.) The control of such systems is frequently on monomer concentration in the gas phase over the reaction mixture. This is because gas phase concentrations vary less with temperature, pressure, and solvent. What monomer composition in the gas phase is needed to produce a copolymer containing 30 mol% propylene. The reactivity ratio of ethylene (rj) has been found to be 5, based on gas phase concentrations. 

Ethylene-propylene rubbers (EPR) are basically random copolymers of ethylene and propylene, with 60-70% (w/w) ethylene. Polyethylene and polypropylene are homopolymers that display too high a degree of crystallinity to be used as elastomers. Nevertheless, random copolymerization produces linear chains with sufficient structural irregularity to prevent crystallization. The copdlymerization process leads to amorphous, fully saturated chains. 

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