Effect of Reaction Variables

Isoselectivity also varies with the initiator and coinitiator concentrations. Isoselectivity decreases with increasing zirconocene and MAO concentrations in the polymerization of 1-hexene by Me2Si(H4lnd)2ZrCl2/MAO [Zhao et al., 2000], For polymerization at 50°C with [M] = 8.0 mol L mmmm) decreases from 0.90 to 0.76 when the zirconocene concentration increases from 5.2 to 104 iM with [MAO] kept constant at 62 mM. When [MAO] is increased from 4.0 to 62 mM with [zirconocene] constant at 52 pM, mmmm) decreases from 0.92 to 0.84. Polymerization at higher initiator and coinitiator concentrations at constant monomer concentration is essentially equivalent to polymerization at lower monomer concentrations at constant initiator and coinitiator concentrations. The amount of monomer available per propagating species decreases, there is more time available for epimerization, and isoselectivity decreases. 

In summary, it is important to emphasize that the course of the polymerization depends not only on the initiator structure but also quite strongly on reaction variables such as temperature and reactant concentrations. 

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The first paper of this series concerns the effects of f-BuX, Me3Al, Et2AlX and EtAlCl2, and MeX on PIB yields and polymerization rates. The second paper1 will survey and discuss the effects of reaction variables on molecular weights of PIB and molecular weight control in isobutylene polymerization. 

De Bruijn et al.26 30 used chromatographic and spectroscopic techniques to analyze the effect of reaction variables (such as pH and monosaccharide concentration) on the product profile and developed a reaction model (see Fig. 9) that emphasized the role of a-dicarbonyl compounds. Some of the features of the model shown in Fig. 9 are ... 

Table 6E Effects of reaction variables on substitution and elimination reactions...

Ammoxidation of propane over Fe-zeolites effect of reaction variables, catalyst composition and catalyst structure... 

H. Effect of Reaction Variables on the Photochemical Process Proper... 

Table I. The Effect of Reaction Variables in the Reductive Carbonylation of Methanol ...

The success of this approach is illustrated by Fig. 2, which displays results for the reaction of Fig. 1. This plot depicts the linear increase in the amounts of primary products (including their derivatives) as a function of total product concentration, which is also linear in Y, the abscissa of Fig. 1. Experimental data treated in this manner thus indicate the selectivity to primary products formed by a reaction, regardless of the extent of secondary reactions, and meaningful interpretation of the effects of reaction variables becomes possible. 

Takegami et al. (147) reexamined the reaction of olefins with cobalt hydrocarbonyl to determine the effect of reaction variables and the possibility of isomerization on the structure of the acylcobalt carbonyls formed. Products were recovered as their ethyl esters as described previously. Additionally, the uptake of carbon monoxide was measured. This is important since the presence of an acylcobalt tricarbonyl can be inferred when the amount of ester produced exceeds the amount of carbon monoxide absorbed. 

Bhanage BM, S-i Fujita, Ikushima Y et al (2003) Synthesis of dimethyl carbonate and glycols from carbon dioxide, epoxides and methanol using heterogeneous Mg containing smectite catalysts effect of reaction variables on activity and selectivity performance. Green Chem 5(1) 71—75... 

In addition to a better understanding of the effect of reaction variables on products, rates and molecular weights, this work has also led to new mechanistic concepts such as termination by hydridation and to the optimization of cationic graft-copolymer synthesis. 

Table 1 is a compilation of relatively large scale copolymerization experiments carried out to collect material sufficient for characterization and jdiysical property studies. Results of experiments conducted to elucidate the effects of reaction variables on reactivity ratios i.e., small scale runs ( 20 ml), are listed separately later. 

Effect of reaction variables on the different stages of a three phase catalytic process.24... 

Effect of Reaction Variables. Correlations between the types of product obtained and several reaction variables were studied briefly, and are discussed in the following paragraphs. 

It is obvious from the above considerations, that it is difficult to study one variable at a time, since they interplay with each other. As in the question of mechanism, a better understanding of the effect of reaction variables will have to await more fundamental studies involving plasma probing, etc. 

Prediction of the pathway a secondary substrate will follow is another direct application of the logical consequences of the two competing mechanisms. Read the lust portion of Section 7-S particularly carefully, because it presents a classic example of the use of mechanistic information to explain (and predict) the effects of reaction variables on possible reaction pathways. 

Reference [85] gives many details of the effect of reaction variables such as the temperature at which the AIBN is added the effects of different levels of AIBN, PVP, and styrene on particle size the effect of adding either toluene or water to the reaction medium the addition of water initially or after nucleation and the effect of the level of divinylbenzene and the method of its addition. 

Table 11. Effects of Reaction Variables on Rates and Product Distributions in Hydroformyiations Using HRhfCOjPPhsis ...

Magnesium.— The exchange route to perfluoroalkylmagnesium halides, RfX + RMgBr RpMgBr + RX (X = Br or I R = alkyl or aryl), has received attention by two groups, one of which has presented - in detail its conclusions regarding the effects of reaction variables on yields (see Schemes 3 and 4 - for... 

Gomes D, Borges C, Pinto JC. Effects of reaction variables on the reproducibility of the syntheses of poly-1,3,4-oxadiazole. Polymer 2004 45(15) 4997-5004. 

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