Ethylene, copolymerization

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

Table 4.9 Structures Formed by Backbiting in Ethylene Copolymerizations ...

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. 

An ethylene copolymerization catalyst was prepared by Baita et al. (3) consisting of magnesium chloride/ethyl alcohol adduct, triethyl aluminum, and titanium tetrachloride. 

W. Wang and K. Nomura, Remarkable effects of aluminum cocatalyst and comonomer in ethylene copolymerizations catalyzed by (arylim-ido)(aryloxo) vanadium complexes efficient synthesis of high molecular weight ethylene/norbomene copolymer, Macromolecules, 38(14) 5905-5913, July 2005. 

In a typical ethylene copolymerization condition, the comonomer (i.e. p-methylstyrene) was mixed with solvent (toluene or hexane) and methylaluminoxane (MAO) (30 wt% in toluene) needed in a Parr 450 ml stainless autoclave equipped with a mechanical stirrer. The sealed reactor was then saturated with 45 psi ethylene gas at 30 or 53 °C before... 

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... 

Historically, high-pressure free radical copolymerization has been used to produce highly branched, ill-defined copolymers of ethylene and various polar monomers. Although these materials are in production and extensively used throughout the world, the controlled incorporation of polar functionality coupled with linear polymer structure is still desired to improve material properties. Recent focus in this area has led to the development of new transition metal catalysts for ethylene copolymerization however, due to the electro-philicity of the metal centers in these catalysts, polar functional groups often coordinate with the metal center, effectively poisoning the catalyst. There has b een some success, but comonomer incorporation is hard to control, leading to end-functionalized, branched polyethylenes [44, 46]. These results are undesirable due to low incorporation of polar monomer into the polymer as well... 

Table 11. Reactivity ratios in propylene-ethylene copolymerization...

The fact that ethylene will copolymerize at high pressures is rather fortunate from not only a commercial but also a theoretical view, since it has long been believed that monomer reactivity ratios might be better correlated according to a scheme based on ethylene rather than the currently used Q-e correlation in which styrene is taken as the reference standard. However, until recently no quantitative data on ethylene copolymerizations have been available upon which to base such a scheme. 

Thus, the copolymerization ideality in ethylene copolymerizations—i.e., the proximity of rjr2 to unity—is strictly dependent on the e value of the comonomer. Hence, we see that since ethylene, because of its lack of substituent groups, resides at the center of the e scale, relatively large positive or negative e values may be tolerated without seriously affecting the ideality of the copolymerization. 

Some data recently obtained on high pressure ethylene copolymerizations illustrate the quantitative aspects of an ethylene-based Q-e scheme (6). In Figures 3 and 4 copolymer composition curves for the ethylene-vinyl chloride and the ethylene-vinyl acetate copolymerizations are given. The monomer reactivity ratios for these two systems are tabulated in Table III along with Q values and e values for vinyl chloride and vinyl acetate calculated using ethylene as the standard (Q = 1.0 and g = 0). These Q and e values may be compared with those obtained using styrene as the standard. 

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

Chain propagation of CO/ethylene copolymerization proceeds by a strictly alternating insertion of CO and olefin monomers in the growing chain. It is safe to assume that double CO insertion does not occur for thermodynamic reasons [Ic]. However, the complete absence of double ethylene insertions is remarkable because ethylene insertion in a Pd-alkyl species must be exothermic by about 20 kcal/mol (84 kJ mol). The observation of strict alternation is the more surprising since the same palladium catalysts also efficiently dimerize ethylene to butenes [25]. The perfect alternation is maintained even in the presence of very low concentrations of carbon monoxide. When starting abatch polymerization at a high ethylene/CO ratio, error-free copolymer is produced until all the CO is consumed then the system starts forming butenes (with some catalyst systems at about twice the rate of copolymerization ). 

We are aware of only one other example in which polymerization (in this case CO/ethylene copolymerization) is promoted by pentafluorophenyl abstraction from B(C6F5)3. Barlow, G.K., Boyle,... 

Kinzl, M. et al., SAFT modeling of inert-gas effects on the cloud-point pressures in ethylene copolymerization systems poly(ethylene-co-vinyl acetate)- -vinyl acetate-i-ethylene and poly(ethylene-co-hexene-l)-thexene-l-tethylene with carbon dioxide, nitrogen or -butane, Ind. Eng. Ghent. Res., 39, 541-546, 2000. 

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