Functionalized negative neighboring group effect

Other groups such as esters, silylethers, and imides are also successfully incorporated through ADMET depolymerization with 14 (Fig. 8.21).49 For an ester functionality, at least two methylene spacer units must be present between die olefin site and die functional group in order to achieve depolymerization. This is due to die negative neighboring group effect, a deactivation of the catalyst by coordination of the functionality heteroatoms to die catalyst.50 By physically... 

Keywords Acyclic diene metathesis polymerization, ADMET, Condensation polymerization Functionalized polymers, Negative neighboring group effect, Branched polyethylene... 

Abstract The structure/reactivity behavior for pure hydrocarbon diene monomers, and for dienes containing heteroatoms has been examined. Steric hindrance is the controlling factor for hydrocarbon monomers, and intramolecular electronic interactions determine the reactivity of dienes possessing heteroatom functionality. This electronic interaction phenomenon is termed the "Negative Neighboring Group Effect". 

The parameter n reflects the measure of deviation of the system from the behavior of the monomeric acid where n = 1, i.e., it characterizes the degree of interaction between the neighboring functional groups of the macroion. The value of n depends on the structure of the polyelectrolyte and the nature of the counterion pK = pK0 — log (1 — a)/a is the negative decadic logarithm of the effective dissociation constant of the carboxylic CP depending on a. 

Generally these globular dendritic architectures offer several advantages over other kinds of organic polymers, such as the full exposure of the catalytic centers to the environment. In contrast to linear or cross-Hnked polymeric supports, which can partially hide catalytic centers, the functional groups are located on the surface of the dendritic nanoparticle and diffusional Hmitations are less relevant Furthermore the close proximity of the catalytic centers on the surface of the dendritic polymer can enhance the catalytic activity by multiple complexation or even cooperativity. This behavior is described as positive dendritic effect. However, in some cases a negative dendritic effect was observed, which is caused by an undesired interaction or electron transfer between the neighboring catalytic centers on the surface of the dendrimer [70]. 

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