Effect Of Chain Size Research Articles

The Effect of Chain Size and Customer Type on Company Survival: Evidence from Multi-Unit Restaurants

It is commonly believed that economies of scale in branding, operation, and learning provide large chains’ dominance in the retailing industry. Anecdotal and systematic evidence, however, show larg...

The effect of chain size on the modeling of second sphere effects in biomimetic complexes

In this paper, we describe a new method for the systematic synthesis of catalytic dinuclear Zn(II) hydrolases incorporating second coordination sphere effects by using a polyamidoamine dendrimer as a secondary chain model. Six complexes bearing different dendrimer generations were studied in the hydrolysis of 2-hydroxypropyl-4-nitrophenyl-phosphate (HPNP) and sets of kinetic data were compared in order to better understand the effect of the chain model on the reactivity. The results indicate that a chain of 4000gmol−1 is sufficient to represent the second sphere effect in our model. Although the activation entropy ΔS‡ was significantly increased, the kcat value was not increased, due to unfavorable changes in ΔH‡. The dinuclear catalytic center remained intact, acting through the same mechanism, which opens new possibilities for the rational functionalization at this chain length to further increase the complex activity.

Electrochemical One‐Electron Oxidation of Low‐Generation Polyamidoamine‐Type Dendrimers with a 1,4‐Phenylenediamine Core

A series of polyamidoamine (PAMAM)-type dendrimers with a 1,4-phenylenediamine (PD) core is prepared from PD by procedures including Michael addition of methyl acrylate followed by aminolysis with 1,2-ethanediamine. Their one-electron oxidation potentials are determined by differential pulse voltammetry (DPV) in methanol, acetonitrile, dichloromethane, and dimethyl sulfoxide. The dendrimers are more difficult to oxidize than N,N,N',N'-tetramethyl-p-phenylenediamine (TMePD). The oxidation potentials decrease with increasing dendrimer generation up to G0.5, after which the potential is essentially constant up to G2.0. The structures of both the neutral species and the radical cations are studied by DFT calculations at the B3LYP/6-31G(d,p) level of theory, which include a series of simple PDs for comparison. The data show that the structural arrangement close to the PD core is similar to that of N,N,N',N'-tetra-n-alkyl-p-phenylenediamines, including a planar arrangement of the atoms linked to the two PD nitrogen atoms. Thus, the effect of chain size on the oxidation potential appears to be caused primarily by a simple electronic effect. The calculations indicate considerable reorientation of the dendrimer side chains on oxidation, presumably caused by interactions between the positive charge centered at the core and the neighboring ester or amide dipoles. The relative ease of oxidation of TMePD and the lowest members of the series of the dendrimers can be reproduced theoretically only when solvation was included in the calculations. The DPV peak heights vary approximately as predicted from the Stokes-Einstein-Sutherland equation, but the variation of the relative effective radii with the size of the dendrimer is much larger than predicted from the radii obtained by the DFT calculations, that is, the dendrimers exist in solution mainly as aggregates.

Monte Carlo simulation of star/linear and star/star blends with chemically identicalmonomers

The effects of chain size and architectural asymmetry on the miscibility of blendswith chemically identical monomers, differing only in their molecular weight andarchitecture, are studied via Monte Carlo simulation by using the bond fluctuationmodel. Namely, we consider blends composed of linear/linear, star/linear andstar/star chains. We found that linear/linear blends are more miscible than thecorresponding star/star mixtures. In star/linear blends, the increase in the volume fractionof the star chains increases the miscibility. For both star/linear and star/starblends, the miscibility decreases with the increase in star functionality. When weincrease the molecular weight of linear chains of star/linear mixtures the miscibilitydecreases. Our findings are compared with recent analytical and experimentalresults.

Effective Interaction Parameters of Star/Star, Ring/Ring, and Ring/Linear Chemically Identical Blends

The effects of chain size and architectural asymmetry on the miscibility of chemically identical polymer blends composed of star/star, ring/ring, and ring/linear chains are studied by means of an analytical theory. The free energy of these blends is obtained through the summation of the series of the one-loop diagrams at any dimensionality d. From the spinodal equation, we find that for the same total molecular weights the effective repulsions between ring/ring species are higher than those of linear/ linear blends and higher than those of the symmetrical star/star blends of four branches but smaller than the respective interactions of star/star blends where both species have five arms. At d = 3 no phase separation is found for blends composed of ring/ring and ring/linear chains at any size disparity or volume fraction. The same is true in the case of blends composed of star/star or star/linear chains with a few or a moderate number of arms in agreement with recent experimental and theoretical results.