Homogeneous polymerization of ethylene

Ronca S, Forte G, Ailianou A, Komfield JA, Rastogi S (2012) Direct route to colloidal UHMWPE by including LLDPE in solution during homogeneous polymerization of ethylene. ACS Macro Lett 1 1116-1120... 

Mahdavi H, Badiei A, Zohuri GH, Rezaee A, Jamjah R, Ahmadjo SJ (2007) Homogeneous polymerization of ethylene using an iron-based metal catalyst system. J Appl Polym Sci 103 (3) 1517-1522. doi 10.1002/app.24949... 

The polymerization of ethylene was carried out in an identical way with these heterogeneous catalysts as with the homogeneous systems. Typical results are given in Table XII and show that the Si-0 ligand enhances the activity of the transition metal site for polymerization. Some of the higher activities are minimum values since the concentration of ethylene in the diluent is well below equilibrium concentrations and with these conditions the process is diffusion controlled. 

Non-metallocene complexes, such as aryloxide 31 and amide 138, have also been utilized as catalyst systems for the polymerization of a-olefins. Moreover, the homogeneous olefin polymerization catalysts have been extended to metals other than those in Group 4, as described in Sect. 7. Complexes such as mono(cyclopentadienyl)mono(diene) are in isoelectronic relationship with Group 4 metallocenes and they have been found to initiate the living polymerization of ethylene. These studies will being further progress to the chemistry of homogeneous polymerization catalysts. 

Many homogeneous catalytic processes, in particular of anionic nature, are known, in which the polymerization takes place by stepwise addition (polymerization of ethylene oxide (34) of ethylene at low pressure and temperature with ALfia (7, 35), of styrene by Szwarc catalysts (36), for which the growth of the macromolecule can last for a very long time). This led some researchers to talk of a life of macromolecules and of living molecules (37). 

As mentioned in Section 9.3, Jackson (141) has obtained estimates of the chain-transfer coefficient of the growing radical with polymer in the free-radical polymerization of ethylene, C,p, by choosing the value so as to fit the MWD. As the polymerization conditions for the polymers mentioned in Table 10.1 are not disclosed, it is necessary to choose typical conditions 220° C and 2000 atm will be selected. Under these conditions Ctp, the ratio of the rate constant for attack on polymer (per monomer unit) to that for propagation, in a homogeneous phase, was found to be about 4.0 x 10 3. This is in good agreement with the known transfer coefficients for the lower alkanes (160), when allowance is made for the differences in pressure and temperature (100). The relation between Ctp and k is ... 

The first section of this chapter describes the most important high pressure process run under homogeneous conditions to manufacture Low Density PolyEthylene (LDPE). The radical polymerization of ethylene to LDPE is carried out in tubular reactors or in stirred autoclaves. Tubular reactors exhibit higher capacities than stirred autoclaves. The latter are preferred to produce ethylene copolymers having a higher comonomer content. 

Polymerization of Ethylene. The initial investigations were carried out using homogeneous organometallic catalysts. The results are shown in Table III. 

An ESI mass spectrometer coupled online to a microreactor was used to intercept the catalytically active cationic intermediates of the Ziegler-Natta polymerization of ethylene with the homogeneous catalyst system [Cp2Zr(Me)Cl]-MAO (MAO = methylaluminoxane). For the first time these intermediates were studied directly in the solution and their catalytic activity proved.60... 

We describe a mechanistic and kinetic study of polymerization of ethylene and 1-hexene by the homogeneous catalyst Cp2ZrCl2-(MeAlO)x-toluene. 

Anionic polymerization of ethylene has been used to prepare terminally functionalized ethylene oligomers. The reaction proceeds as shown in equation (12). Phosphite as well as phosphine-hmctionalized ethylene oligomers have been prepared. Nickel(O) phosphine complexes can be bound to such a functionalized oligomer. The bound complexes have similar activity as their homogeneous counterparts for the cyclooligomerization of butadiene. 

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