Chain separation

Reasons for these trends are clearly related to the polarity of the plasticizer and its abiUty to impart free volume by chain separation. Differences in polarity affect the temperature at which the plasticizer can penetrate the polymer matrix and the magnitude of the interaction with the polymer chain that results. 

Figure 4-4. Schematic rcprcsenlalion of ihc one-clcclron structure of a single siilbcnc molecule and that of a cofacial dimer formed by iwo chains separated by 4 A. lire INDO-ealculated energy splil ot the HOMO and LUMO levels when going from Ihc isolated molecule to the dimer are also given.

In a regime of strong interaction between the chains no optical coupling between the ground slate and the lowest excited state occurs. The absence of coupling, however, has a different origin. Indeed, below 7 A, the LCAO coefficients start to delocalize over the two chains and the wavefunclions become entirely symmetric below 5 A due to an efficient exchange of electrons between the chains. This delocalization of the wavcfunclion is not taken into account in the molecular exciton model, which therefore becomes unreliable at short chain separations. Analysis of the one-electron structure of the complexes indicates that the... 

Figure 4-9. INDO/SCI-simulalcd absorption and emission spectra of two slilbene molecules with a huge interchain distance (solid lines) and those of a cofacial dimer formed by two slilbene chains separated by 4 A (dolled lines).

Figure 16-22. Molecular packing of Oocl-OPV3-CN. The oclyloxy side-chains separate (lie non-planar ir-systcms.

This series of polymers made it possible to investigate the contribution of each type of pendant chain separately. Poly(Dat-rym), the polymer carrying no pendant chains at all, was virtually insoluble in all common organic solvents. Due to its thermal instability in the molten state, poly(Dat-Tym) could be neither compression-nor injection-molded. In this respect, the processibiUty of poly(Dat-Tym) was not improved as compared to conventional poly(L-tyrosine). 

After It has been determined which chain In the variant Is aberrant, specific structural studies are required. Several procedures are available which differ from one laboratory to the other and Include chain separation by column chromatography, modification of the sulfhydryl groups through reaction with... 

The kinetics of reactions of bifunctional compounds are especially significant in relation to polymer reactions. The esterification rate constants shown in the third column (B) of Table V for the homologous series of dibasic acids do not differ greatly from those for the monobasic acids. These differences vanish as the length of chain separating the carboxyl groups increases. 

When collagen is heated, it is denaturated, losing its structure the polypeptide chains separate and unwind, and, as the collagen cools down, it soaks up surrounding water and forms gelatin. 

Here c is the polymer concentration by weight. < the density of the polymer, a an effective bond length or measure of the coil dimensions, and to the monomeric friction factor. The subscript zero indicates the pure polymer. Since 2 (H), the mean-square end-to-end chain separation, the viscosity will be directly proportional to the polymer concentration unless the plasticizer modifies the coil swelling. At high molecular weight the monomeric friction factor is increased by the factor (MIMf)" and M, is increased relative to the undiluted polymer [equation (55)]. Thus... 

The side chain separation varies in a range of 1 nm or slightly above. The network of aqueous domains exhibits a percolation threshold at a volume fraction of 10%, which is in line with the value determined from conductivity studies. This value is similar to the theoretical percolation threshold for bond percolation on a face-centered cubic lattice. It indicates a highly interconnected network of water nanochannels. Notably, this percolation threshold is markedly smaller, and thus more realistic, than those found in atomistic simulations, which were not able to reproduce experimental values. 

Calculations in Roudgar et al. focused on the shortest SGs (i.e., CF3SO3H) under conditions of minimal hydration (i.e., with one H2O per SG). The main parameter considered is the nearest neighbor distance of the terminal, fixed C atoms. It was varied from 5 A < dec 12 A, which encompasses the range of side chain separations found in prototypical ionomer membranes. The VASP based on DFT was used. Figure 6.13 displays the formation... 

In step four the bottoms are mixed with water and a trace of sulfuric acid. The chains separate from the aluminum in favor of a hydrogen atom, creating the higher alcohols and aluminum hydroxide, Al (OH)3, which drops out of solution as a precipitate. The aluminum product can be readily dehydrated to alumina, AI2O3, and sold. Some processes use sulfuric acid, H2SO4, to do the hydrolyzing instead of water. That results in by-product aluminum sulfate, A1(S04)3, a marketable but less valuable product than alumina. 

If a carbon chain separates an electron donor (D) and electron acceptor (A) sites in the same molecule, the exiplex-resembling state may originate on photoirradiation. Such an exiplex state represents some resonance hybrid of the electron-transfer configuration [D+ -(CH2) -A ] mixed with the locally excited configuration [D -(CH2) -A] or [D-(CH2) -A ]. 

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