Effect of Initiator Structure

C2 ansa metallocenes are inherently isoselective, but the degree of isoselectivity as well as activity and polymer molecular weight vary considerably depending on the specific 

The introduction of heteroatoms into the ligands via alkoxy and trisubstituted amino groups has been explored to improve initiator performance through electronic effects. This approach is not promising as initiator performance deteriorates with very few exceptions. The exceptions do not result in performance enhancements at best, performance is 

Bisfluorenyl zirconocenes generally are neither highly active nor highly isoselective. 

Some 3,1-placements (CH2CH2CH2) are observed in propene polymerization, a result of 

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Tang W, Matyjaszewski K (2007) Effects of initiator structure on activation rate constants in ATRP. Macromolecules 40 1858-1863... 

Fig. 2 Effect of initiator structures on ATRP activation rate constants (fcact) with Cu X/ N,N,N, N, N"-pentamethyldiethylenettiamine (PMDETA) (X = Br or Cl) in MeCN at 35 °C. 3° red 2° blue 1° black isothiocyanate/thiocyanate Irft half-filled chloride open bromide filled iodide bottom half-filled amide inverted filled triangle benzyl filled triangle ester open square nitrile open circle phenyl ester open diamond. Reprinted with permission from American Chemical Society [42]...

O.N. Senkov, E.V. Konopleva, and E.G. Ponyatovsky, The effect of initial phase content and structure on workability of a hydrogen-alloyed titanium alloy, Fiz. Met. Metallovedeniye, 77 142 (1994). 

Chen, Y., Puskas, J.E., and Tomkins, M. Investigation of the effect of epoxide structure on the initiation efficiency in isobutylene pol3mierizations initiated by epoxide/TiCLt systems, Eur. Polym. J., 39, 2147-2153, 2003. 

The theories that attempt to describe the initial event in sweet-taste stimulation will be discussed, as will some of the practical attempts to isolate sweet-receptor molecules. Relevant, behavioral data will be examined, particularly where the effects of molecular structure on behavior responses are being evaluated. 

The Effect of Initiator Concentration on the Rate of Polymerization. BME, 2,2-dimethoxy-2-phenyl acetophenone, 2-hydroxy-2,2-dimethyl acetophenone and Darocur-3331 (its structure is not known) were chosen for further evaluation on the effect of initiator concentration on the rate of polymerization. They were chosen because they are the among the most active or the least active initiator in polymerizing HEMA. 

The study of heterogeneous catalysis with the emphasis on the effects of reactant structure stimulates consideration of the reacting system in terms of mutual interactions. Modification of the catalyst surface by the action of reactants is a part of these interactions. This idea is not new, but hitherto little evidence supported it now it is an inherent component of the accepted mechanism of elimination reactions. In general, the working surface may be quite different from the initial surface. Even the solvent may participate in the mechanism, as the results of the Delft school (125, 161, 162) indicate, by temporally accommodating hydrogen species formed in a reaction step from the reactants or hydrogen molecules on the surface. 

Kwak Y, Matyjaszewski K (2008) Effect of initiator and ligand structures on ATRP of styrene and methyl methacrylate initiated by alkyl dithiocarbamate. Macromolecules 41 6627-6635... 

Warren Kaplan argues that we should expect hybrid structures to appear in the pharmaceutical industries of the important middle-income producers of generic medicines (e.g., India). Notwithstanding the possible effect of these structures on pharmaceutical innovation in middle-income countries, this restructuring is likely to have important consequences for access to affordable medicines. The effect of these hybrid structures on real pharmaceutical innovation in the established pharmaceutical industry and in the newer public-private initiatives is still unclear. 

EMPIRICAL CORRELATIONS SUGGESTING IMPORTANCE OF INITIAL ATTACK. A number of empirical correlations have been developed between structure of complex molecules and knock. The effects of particular structural features which... 

Emission of cool flame radiation is associated with an early stage in the preflame reactions of most hydrocarbons, as evidenced by the fact that the appearance of cool flames occurs at the same time as the initial pressure development. At a later time in the cycle a second radiation phenomena, described as a blue flame, has been observed under certain conditions (36, 124). A second cool flame also occurring late in the cycle may be the same phenomenon (81, 103, 131). While the importance of cool flame and blue flame phenomena in the over-all reaction mechanism is not fully understood, their occurrences can be used to mark certain stages in the course of the preflame reactions. This principle has been used extensively in studying the effect of hydrocarbon structure, physical variables, and additives on engine preknock reactions. 

In our opinion, the area of this type of copolymerization is still open to discussion and research, and this suggestion concerns mainly the mechanism of copolymerization, formation of active centres in the initiation by Lewis bases, the influence of proton donors on the course of copolymerization, and tbe effect of the structure of the initiator on the rate of copolymerization. It is necessary, however, to study the copolymerization on model compounds. 

Figure 1. (a) Representative LDA trajectory with time points indicating significant changes in electronic structure, (b) Effect of initial velocity, v0. 

Theoretical calculations of sticking are challenging, due to the interplay of the Coulomb and strong interactions in a non-adiabatic few-body system, yet recent predictions, including the effects of nuclear structure and the deviations from the standard sudden approximation, now converge to a few percent [36], They cannot, however, be readily compared to experiment because most measurements are primarily sensitive to final sticking which is a combination of initial... 

For ions of initial structure (CH3CH2CH=SH)+ and (CH3CH=SCH3)+, average deuterium isotope effects, i, for metastable ion decompositions effecting loss of hydrogen sulphide of 2.3 and 1.8, respectively, were determined [136]. 

The polymers were synthesized by hydride polyaddition with 0.01N platinum-hydrochloric acid-tetrahydrofuran solution as the catalyst. The catalyst concentration equaled 5xl0 6 g per 1 mole of vinyl component in the temperature range of 60 - 150°C. It has been found that the reaction pro-ceeding at high temperatures displays formation of branched structures. The effect of initial mo-nomers structure on the formation rate of polymers, as well as on physical and chemical properties and structural features of synthesized polymers are traced. The reaction proceeds by the general scheme as follows [80] ... 

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