Polymerization kinetics ethylene

Fig. 27 Ethylene polymerization kinetic curves of catalysts activated by TEA cocatalyst during slurry polymerizatimi (a) Phillips catalyst al) and Cat-A/1.5 catalyst a2) (Al/Cr molar ratio = 20.0) (b) Cat-A/1.5 catalyst (W) and S-2 catalyst b2) (Al/Cr molar ratio = 15.0). Polymerization conditions catalyst amount, 160 mg polymerization temperature, 90°C ethylene pressure, 0.15 MPa solvent, heptane, 70 mL...

Choi KY, Tang S, Yoon Modehng of ethylene polymerization kinetics over supported chromium oxide catalysts, Macromol Theory Simul 13(2) 169—177, 2004. 

Fang Y, LiuB, Terano M Various activation procedures of Phillips catalyst for ethylene polymerization, Kinet Catal 47(2) 295—302, 2006. 

The shape of the kinetic curves depends on the catalyst type and polymerization conditions (ethylene pressure, temperature, concentration of inhibitors in reaction medium) (89, 97, 98). The types of the kinetic curves obtained. at ethylene polymerization under various conditions are presented in Fig. 1. 

Fig. 1. Examples of the kinetic curves during ethylene polymerization by chromium oxide catalysts. Support—SiOs temperature—80°C polymerization at constant ethylene pressure in perfect mixing reactor. Curve 1—catalyst reduced by CO at 300°C. Curve 2— catalyst activated in vacuum (400°C) polymerization in the case of (1) and (2) in solvent (heptane) ethylene pressure 10 kg/cm2 02 content in ethylene 1 ppm, HsO 3 ppm. Curves 3, 4, 5, 6—catalyst activated in vacuum (400°C) polymerization without solvent ethylene pressure 19 (curve 3), 13 (curve 4), 4 (curve 5), and 2 (curve 6) kg/cm2 02 content in ethylene 1 ppm, HsO = 12 ppm.

The change of shape of the kinetic curves with monomer and inhibitor concentration at ethylene polymerization by chromium oxide catalysts may be satisfactory described 115) by the kinetic model based on reactions (8)-(14). 

In Benning el al. (146) some data on the kinetics of ethylene polymerization in the presence of TiCl2 activated by ball-milling are given. Polymerization was studied at 140-260°C (the solution process in cyclohexane). The first orders of the polymerization rate on the monomer and catalyst concentrations have been established. The polymerization decreased with temperature a sharp drop in rates at about 180-200°C was observed. 

The kinetics of ethylene polymerization at temperatures below 90°C (the slurry process) were studied in Bukatov el al. (157, 159). The steady-state polymerization rate was observed the first order in the polymerize tion rate with respect to ethylene and the catalyst concentration was found. The polymerization rate increased on increasing the polymerization temperature from 20° to 80°C (Eeu = 7.5 0.5 kcal/mole). 

Radiolytic ethylene destruction occurs with a yield of ca. 20 molecules consumed/100 e.v. (36, 48). Products containing up to six carbons account for ca. 60% of that amount, and can be ascribed to free radical reactions, molecular detachments, and low order ion-molecule reactions (32). This leaves only eight molecules/100 e.v. which may have formed ethylene polymer, corresponding to a chain length of only 2.1 molecules/ ion. Even if we assumed that ethylene destruction were entirely the result of ionic polymerization, only about five ethylene molecules would be involved per ion pair. The absence of ionic polymerization can also be demonstrated by the results of the gamma ray initiated polymerization of ethylene, whose kinetics can be completely explained on the basis of conventional free radical reactions and known rate constants for these processes (32). An increase above the expected rates occurs only at pressures in excess of ca. 20 atmospheres (10). The virtual absence of ionic polymerization can be regarded as one of the most surprising aspects of the radiation chemistry of ethylene. 

The kinetics of the reaction has been studied by IR as well as laser reflection interferometry (LRI) [21,145]. The amount of polymer grown on the surface was measured from the LRI signal as a function of time. It was shown that propylene polymerization was about 30 times slower than ethylene polymerization [145]. hi addition, Kim et al. estimated the polymerization ac-... 

Scheme 4 Mechanism of chain growth for a all Pd(II) polymerizations and ethylene polymerizations with Ni(II), and b a-olefin polymerizations with Ni(II). Specific kinetic data shown for Ni catalyst 1.15b [63]...

The Effect of Crosslinker Concentration on the Rate of Polymerization. Ethylene glycol dimethacrylate is used most frequently as the crosslinker for HEMA formulations useful in contact lens manufacturing. To demonstrate the effect of crosslinker concentration on the curing rate, formulations derived from HEMA/Glycerine/BME at 85/15/0.17, while varying EGDMA (from 0.34 to 0.68), the peak times were about the same (3.73 and 3.61 minutes respectively). This is reasonable due to the similarity in molecular structure of the crosslinker and the monomer, and the low amount of crosslinker used. The possible presence of other crosslinker, such as the dimerization product of HEMA, is even less a factor to be considered in polymerization kinetics, due to low concentration (normally much less than 0.1 %, in-house information). 

Jabarin, S. A. and Lofgren, E. A., Solid state polymerization of poly (ethylene terephthalate) kinetic and property parameters, J. Appl. Polym. Sci., 5315-5335 (1986). 

In any case, such chain transfer processes lead to a continuous increase of the molecular weight of the alkylaluminum compounds during the polymerization. It is, however, possible that alkylaluminum molecules having a low molecular weight are regenerated by a mechanism similar to those reported in the study of the kinetic behavior of ethylene polymerization, in the presence of trialkylaluminum 36) or through a dissociation to a hydride ... 

Title Catalyst for Ethylene Polymerization, Preparation Thereof, and Method for Controlling the Polymerization Kinetic Behavior of Said Catalyst... 

Chien, J. C. W. Kinetics of ethylene polymerization catalyzed by bis(cyclo-pentadienyl)-titanium dichloride-dimethylaluminium chloride. J. Amer. Chem. Soc. 81, 86 (1959). 

CoCp unit C-C bond activation, 7, 80 CoCp unit CH activation, 7, 79 in ethylene polymerization, 7, 81 substituted ligands, 7, 71 synthetic applications, 7, 74 with )4-cyclobutadiene applications, 7, 66 new ligand preparation, 7, 70 with )4-(cyclobutadiene) ligands, 7, 59 dendrimeric cobaltocenium derivatives, 7, 88 with fullerenes, 7, 51 HP-NMR and HP-IR studies, 1, 488 with rj -hydrocarbyl units, 7, 8 immobilized, as polymer support, 12, 681 kinetic studies, 1, 520 with )3-ligands, 7, 56 with metallaboranes, 3, 158 overview, 7, 1-119... 

All of the studies published to date fail to identify the active catalyst species present in the RLi-TMEDA polymerization of ethylene. The kinetics data of both Hay and Shud and their co-workers fall short in this respect. A more fundamental approach is needed. It may be appropriate at this time to study the 13C- and 7Li-NMR of alkyllithium compounds in the presence of various chelating diamines and polar modifiers such as THF and dimethyl ether. 

Kinetics of High Pressure (Low Density) Ethylene Polymerization... 

Many kinetic studies on the high pressure ethylene polymerization are found in the literature (8-11). All authors agree on the following main reaction steps ... 

Other catalysts, highly active in ethylene polymerization, have been obtained by co-milling MgCl2 with Ti compounds other than chlorides37). Even though these catalysts are active for the propylene polymerization, they are stereospecifically poor and have mainly been used to determine kinetic parameters at short polymerization times 38). 

The Mg/Ti catalysts for polyethylene have been the most widely studied for historical reasons. The most comprehensive kinetic scheme for ethylene polymerization was provided recently by B6hm85) (see Fig. 27). 

Based on the proposed model and on the experimental observation that the polymerization rate is proportional to the monomer concentration, it has been concluded that olefin coordination constitutes the rate determining step. However, the variety in preparation and performance of Mg/Ti catalysts for ethylene polymerization is such that it is impossible to reduce it to a single kinetic scheme, even though the active principle may be, in any case, constituted by MgCl2 89-90-91>. Ethylene polymerization with these catalysts has recently been reviewed 89) and will not be dealt with in detail here. However, it is important to underline that Mg/Ti catalysts for... 

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