Highly polar end groups

One of the first properties of hyperbranched polymers that was reported to differ from those of linear analogs was the high solubility induced by the branched backbone. Kim and Webster [31] reported that hyperbranched polyphenylenes had very good solubility in various solvents as compared to linear polyphenylenes, which have very poor solubility. The solubility depended to a large extent on the structure of the end groups, and thus highly polar end-groups such as carboxylates would make the polyphenylenes even water-soluble. 

Detergents minimize fuel system deposits at low concentrations, and at high concentrations can remove deposits that have already formed. Detergents are molecules that have a highly polar end group and a nonpolar hydrocarbon tail. A conventional amino amide type detergent is shown in... 

Dendritic polymers are used as functional thin layers. Highly branched aromatic polyesters with polar end groups show good response behaviour in gas phase and liquid sensors [46]. Ease of recycling of the expensive platinum complexes (e.g. by nanofiltration) is a positive aspect of the use of such sensor den-drimers [47]. 

Puskas et al. extracted paraffinic deposits from oil wells and pipelines (47). This hydrophobic paraffin derivative had a high molar mass and melting point and contained polar end groups (carbonyls). This paraffinic derivative stabilized water-in-oil emulsions at concentrations of 1 to 2%. 

Whereas the polymers employed by Qiao et al. [133, 206] concerned only star polymers with low Tg (below 48 °C), Li and coworkers [207] studied the construction of macroporous polymeric films on various nonplanar substrates with static breath figures technique, using linear polymers with high Tg. For this purpose, two kinds of linear polymers with high Tg, polystyrene-6-poly(acrylic acid) and polystyrene without polar end groups, were employed to prepare three-dimensional macroporous films on different nonplanar substrates. 

In the absence of lubricant on the slider, the adhesion stress is taken to be the tensile strength of the interface between the slider carbon overcoat (material 1) and the disk lubricant (material 2). It is the force per unit area to separate the two materials. Only dispersion-force contributions to the tensile strength are included in the following, because the high velocity between the slider and disk asperities does not allow time for dipole orientation [19], and there are relatively few polar end groups per unit area of disk surface. An approximate expression for the tensile strength with atoms separated by distance Cjj is derived as follows [20]. 

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. 

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