Chain redistribution

Extrinsic factors (environment) such as the medium conditions also play a large part in the complexation process, especially pH and ionic strength (salt and polyelectrolyte concentrations). Also of prime importance is the way that the complexation itself is conducted, i.e., mixing parameters such as the stoichiometry of the components, the addition rate, and order of addition of the components (kinetic versus thermodynamic). Even if this process is fast and kinetically cOTitroUed (in water without added salt), i.e., far from the thermodynamic equilibrium, it can be followed by a slower stage in which the chains redistribute to a IPEC conformation closer to equilibrium [59]. 

A second process that occurs concurrently with the dissociation— redistribution process is an intermolecular rearrangement by which cyclohexadienone groups move along a polymer chain. The reaction maybe represented as two electrocycHc reactions analogous to a double Fries rearrangement. When the cyclohexadienone reaches a terminal position, the intermediate is the same as in equation 8, and enolization converts it to the phenol (eq. 9). 

This process, which predominates at low temperatures, causes migration of internal ketal stmctures along a chain but does not involve the dissociation to separate aryloxy radicals that occurs during the redistribution process. 

Different locations of parent elements. and Th are generally located in minor phases within host rocks. Due to different U/Th ratios in these phases, recoil from the two chains may be affected by different surrounding matrix characteristics or mineral sizes. Not only might the primary distribution of U and Th be different, but earlier weathering or alteration may also have redistributed U and Th. This is discussed further below. 

The computational efficiency of the dynamics in Step 2 on the 2nnd lattice permits the study of the cohesion (and complete mixing) of two thin films [173]. Time scales for equilibration of the density profile, redistribution of chain ends, and complete intermixing of the chains span several orders of magnitude of time, expressed in MC steps, and are all accessible via the 2nnd simulation [173],... 

The ESA spectra of this series of A-n-A dyes are shown in Fig. 20. They exhibit broad and intense bands in the visible range (400-600 nm for G37,400-630 nm for G38,450-630 nm for G74, and 450-700 nm for G152) and weak bands in the NIR as revealed in Fig. 20 for G38. We observe that lengthening of the conjugation chain leads to a 30-40 nm red shift of the ESA peaks, which is similar to the behavior of D-rc-D polymethine dyes. This red shift ( 30-40 nm) is much smaller than for the linear absorption bands ( 100 nm). Another experimental feature is connected with the redistribution of the ESA magnitude from the shorter to the... 

Schwarzer D, Kutne P, Schroder C, Troe J (2004) Intramolecular vibrational energy redistribution in bridged azulene-anthracene compounds ballistic energy transport through molecular chains. J Chem Phys 121 1754... 

The concept of dynamic silver clusters capable to transfer between molecules was also pointed out recently by Ras et al. for silver clusters prepared by photoactivation using PM A A as scaffold [20], Every specific initial ratio of silver ions to methacrylate unit, Ag+ MAA, results in distinct spectral bands (Fig. 12a, b). Thus, an initial ratio 0.5 1 gives an absorption band at 503 nm, whereas a ratio 3 1 gives a band at 530 nm. The shuttle effect was proven when for a given silver cluster solution with ratio 3 1 and absorption at 530 nm, a blue shift was achieved by the addition of pure PMAA. For instance if the added amount of polymer decreases the ratio Ag+ MAA from 3 1 to 0.5 1, the new optical band will match exactly with the band corresponding to a solution with initial ratio 0.5 1, that is 503 nm (Fig. 12c). The explanation given for this blue shift was the redistribution of the existent silver clusters in PMAA chains over the newly available PMAA chains, in other words that the clusters shuttle from partly clusters-filled chains to empty ones. 

These type of reactions are generally named as "equilibration" or "redistribution" reactions due to the nature of the processes. During the reactions the catalyst can only cleave the (Si-0) bonds in the cyclic or linear species including that of the "end blocker" and growing chains. However, the (Si-R) or (R-X) bonds are stable. Therefore at the end of the reactions the linear oligomers are functionally terminated and the minority (10-15%) cyclic side products are nonfunctional. After elimination of catalyst, the cyclic side products can usually be removed from the system by... 

Fig. 4.7 A schematic representation of a cationic displacement along a polymeric chain above its Tg. (a) An initial activated step (ft) allows the formation of an interstitial pair, the migration of which (c) and (d) is assisted by local free volume redistribution.

Alkane metathesis (AM shown for n-aUcanes in 6), which has also been referred to as disproportionation or redistribution of alkane chains, has great potential in the context of petroleum refining. 

Although for more detailed information it is necessary to consult the original articles, in principle the RBR graph of a reaction consists of a set of solid, dashed, and bold lines, in which the solid lines represent the bonds that are involved in the redistribution process but are not broken, the dashed lines represent the bonds that are broken or formed during the rearrangement, and the bold lines represent the chain of atoms that are unchanged during the conversion and are thus common in both initial and final product. 

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