Ethylene copolymerization with

Backbiting also occurs in ethylene copolymerizations with AN,298 (mcth)acrylatc esters290 and VAc. The structures identified in E-BA... 

These catalysts represent the current state-of-the-art in ethylene copolymerization with polar olefinic monomers, being able to copolymerize a wide variety of polar monomers containing both O and N heteroatoms to generate completely linear, high molecular weight, random copolymers. There are leads to enhance the modest activity of these catalysts, and it will be interesting to watch further developments over the next few years. 

The copolymerization of ethylene with other olefins is affected by the variation of the Al Zr ratio, temperature, and catalyst concentration. These variables lead to changes in the molecular weight and the ethylene content. Higher temperatures lead to increases in the ethylene content and low molecular weights. Investigations of ethylene copolymerization with 1-butene... 

Ethylene copolymerizations with a-olefins relax some of the constraints imposed upon a-olefin homopolymerizations, since while a-olefins insert only at primary palladium alkyl bonds, ethylene will insert at secondary palladium—alkyl bonds as long as they are not adjacent to a tertiary carbon atom. Thus, for an a-olefin with n carbon atoms, the spectrum of the resulting copolymer shows a superposition of resonances for a normal ethylene polymerization with a spectrum containing not only n — 2 branches but also n — 3 (and presumably n — 1) branches, etc. Ethylene can be inserted into any carbon of the a-olefin. 

While a wide range of monomers have been incorporated in ethylene copolymerizations with the palladium a-diimine catalysts, there are also a variety of monomers which slow homopolymerization and are not incorporated into the polymer chain and others which inhibit all polymerization. There is a general trend that removing the polar functionality from the vicinity of the double bond lessens the rate penalty experienced in the copolymerizations. A superior approach is to place a group which blocks doublebond isomerization between the olefinic group and... 

The development of bifunctional catalysts for specific catalytic sequences of reactions in which the product of the first reaction can serve as substrate for the second is of great importance. There are many examples of such reactions. They are, for instance, the monomer-isomerizing polymerization of heptene-2, heptene-3 and 4-methyl-2-pentene and the combination of propene disproportionation with oligomerization, etc. Bifunctional catalysts are most widely used for ethylene copolymerization with a-butene in situ in the production of so-called low-density linear polyethylene (LDLPE). All general methods for LDLPE production are based on incorporation into a PE backbone of short-chain branches, which can be made by catalytic copolymerization of ethylene with a-olefins C3-C10. A macromolecnlar ligand offers wide possibilities of joining the different types of active site in the same matrix (see also Section 12.5.2). 

Copolymerization with a-olefins over a Phillips catalyst is a key method for controlling the density and microstmctures of the polyethylene products in industrial processes. Table 5 also listed the energy barriers for the primary 1,2-insertion of 1-butene and 1-hexene, and the subsequent chain transfer by p-H elimination for all the three kinds of Ti-modified models. The calculated energy barriers showed that Ti-modification could also promote the activity for ethylene copolymerization with a-olefins. The energy differences between comonomer insertion and chain transfer can lead to a conclusion on the effect of Ti-modification on the distribution of the inserted comonomers in polyethylene chains. As listed in Table 5, the difference between energy barriers for chain propagation and for chain transfer decreased for model sites 4g, 12g, and 15g. Therefore, it was reasonable to conclude that Ti-modified catalyst was likely to make low MW polyethylene with much less comonomer insertion because the inserted comonomer mainly led to a chain transfer reaction and left the inserted comonomer at the chain end. As a result, the increased chain termination by comonomer resulted in less SCBs in the low MW fraction and higher density of the polyethylene product for the Ti-modified Phillips catalyst. 

A copolymer is made by polymerizing a mixture of two or more monomers and yields a polymer that incorporates the repeat units of all the monomers used. With a pair of monomers, the ratio of the two repeat units in the polymer is determined by the ratio of the monomers in the feed. As the properties of the polymers are highly dependent on repeat unit composition, the monomer feed unit ratio is closely controlled during reaction. In some instances (such as with ethylene copolymerized with heptene or octene), these can add on branches on the PE chains. This is in fact the case in the synthesis of LLDPE. 

METALLOCENE-CATALYZED ETHYLENE COPOLYMERIZATION WITH 1-OLEFINS... 

Kaminsky and Spiehl also investigated the copolymerization of ethylene with cyclohexene, cycloheptene, and cyclooctene using the isoselective zirconocene rac-Et(Ind)2ZrCl2 under similar conditions to those used for ethylene/CPE copolymerization.Ethylene copolymerization with... 

Ethylene copolymerization with 1-olefin comonomers decrease the polymer vinyl bond concentration because chain transfer to the comonomer ends the polymer chain with a vinylidene bond. Therefore, introducing a 1 -olefin comonomer into the polymerization is expected to lead to lower LCB content, whereas use of... 

Fig. 11. Ethylene copolymerization with 1-hexene T-70°C, Po2h4-2.0 atm, [1-hexene] 0.24 mole/1, and Al/Ti-128 by (a)...

Ethylene copolymerized with other olefins has already been covered above. Ethylene copolymers with polar comonomers are made by the high-pressure route the favoured monomer is vinyl acetate (VAC) which, under the usual reaction conditions, copolymerizes with ethylene ideally. Small amounts of VAC reduce crystallinity and melting point, but increase toughness and flexibility such copolymers (EVAC) are used for tough film, although the moisture permeability is increased by the inclusion of the polar groups. 

Doherty, S., Robins, E.G., Knight J.G., Newman, C.R., Rhodes, B Champion, P.A. and Clegg, W. (2001) Selectivity for the methoxycarbonylation of ethylene versus CO-ethylene copolymerization with catalysts based on C-4-bridged bidentate phosphines and phospholes. Journal of OrganometaUic Chemistry, 640, 182. 

However, Natta and coworkers 25—27) reported that ethylene copolymerized with butene-2 without isomerization and with cydopentene in the presence of Al(hexyl)3/YCl4 or AIEt2Cl/V(acac)3 catalyst to alternating structures (Eqs. 3 and 4) at sufficiently low ethylene concentratiem at -30 C ... 

---