End-group density

The preparation of thin films and layers from dendrimers by self-assembly is a topic of great current interest since it allows the construction of functional interfaces that use specific dendritic properties such as size, shape, porosity, end-group density and multifunctionality. It is also an area of research that benefits substantially from the flexible character intrinsic to most dendrimers. 

To establish a qualitative relationship between the orientation and the layer structure, we examined the number of layers and the end-bead density. We found that the adsorption of functional end-beads results in an alternate ordering in the subsequent layers, i.e., upward orientation in the second layer, downward orientation in the third, etc. Our result provides a direct interpretation of experimental surface energy data for PFPE films with functional end-groups. The nondispersive component of surface energy exhibited an oscillatory pattern with increasing film thickness and was shown to be approximately proportional to end-group density, as demonstrated in our study. ... 

Polybutenes enjoy extensive use as adhesives, caulks, sealants, and glaring compounds. They are used as plasticizers in mbber formulations with butyl mbber, SBR, and natural mbber. In linear low density polyethylene (LLDPE) blends they induce cling to stretch-wrap films. Polybutenes when modified at their unsaturated end groups with polar fiinctionahty are widely employed in lubricants as dispersants. Blends of polybutene with polyolefins produce semisoHd gels that can be used as potting and electrical cable filling materials. 

The isothermal densities within each of the five groups of esters reveal a significant dependence on the molecular structure. At a constant temperature and pressure, the liquid density of the ester decreases with increasing molecular weight and the successive addition of the methylene groups, (X), even though the concentration of the end-groups remained constant. 

The presence of a large number of chain-ends in the fully synthesized dendrimer molecules makes them highly soluble and also readily miscible, for example with other dendrimer solutions. The solubility is controlled by the nature of the end-groups, so that dendrimers with hydrophilic groups, such as hydroxyl or carboxylic acid, at the ends of the branches are soluble in polar solvents, whereas dendrimers with hydrophobic end-groups are soluble in non-polar solvents. The density of the end-groups at the surface of the dendrimer molecule means that they have proportionately more influence on the solubility than in linear polymers. Hence a dendritic polyester has been shown to be more soluble in tetrahydrofuran than an equivalent linear polyester. 

Figure 13. The overall density (volume fraction) profile for DMPC bilayers is shown here. Apart from the distribution of the overall DMPC molecules, the density distribution of the head-group units (including the choline group, the phosphate group and the oxygens of the glycerol unit), and the end groups of the lipid tails are also indicated. In addition, the free-volume profile and the water profile are depicted...

When the conductivity and optical density had attained their maximum values, the spectra showed that double bonds were still present. The acid released by the decomposition of the ester catalyses the subsequent slow cyclisation whereby these terminal double bonds form indanyl end groups [23]. 

Their results are indicative of a low-density region inside the dendrimer with a considerable end-group interaction in the shell. Similar results were obtained from CHARMm molecular mechanics calculations on the dendritic box (Figure 16.12b), which indicated a globular architecture in which the dendritic interior is... 

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