Terminal moieties polar units

Soluble polystyrene supports differ from the terminally functionalized PEGs and polyethylene oligomers discussed above in that the catalyst moieties are attached to polystyrene via pendant groups, the loading of which can affect both the catalyst activity and separability. One example of a simple polystyrene-supported catalyst is the polystyrene copolymer-supported quaternary ammonium salts 66 and 67 [ 103]. These copolymers can be prepared with varying ratios of the styrene unit in the copolymer - the most active catalysts had 20-40 mol% of the vinylbenzylammonium groups in the copolymers. The utility of these catalysts was studied in a variety of solvents in the addition reaction of glycidyl methacrylate and carbon dioxide (Eq. 23). Polar solvents were most useful. The necessary polymer supports for preparation of catalysts 66 and 67 were prepared from chloromethylstyrene-styrene or chloromethyl-styrene-iV,JV-dimethylacrylamide copolymers that were in turn prepared by radical polymerization of the styrene or acrylamide monomers. The catalysts were recycled up to four times with small (ca. 6%) decreases in activity - de-... 

Ng and co-workers recently prepared semi-flexible dendrons up to the third generation (5,89) using ester terminated quaterthiophene and 3,5-dibromophenol as precursor building blocks, where quaterthiophene moieties were used as branching and peripheral units (Chart 1.81) [517]. Spectroscopic studies revealed that solvent polarity has a strong influence on the absorption and emission spectra of the dendrons. Thus, an increase in the solvent polarity produced a bathochromic shift in the absorption and emission spectra and also a dramatic decrease in the fluorescence quantum yield. 

Materials such as 1, 2 and 3 are known as anionic surfactants because the polar head groups are anionic moieties. Cationic surfactants also exist and these, not surprisingly, also exhibit lyotropic liquid crystal phases. Compound 4 is a simple example of a cationic surfactant that consists of an amine with a long terminal chain that has been converted into the ammonium chloride salt. Accordingly, the ammonium cation constitutes the polar head group and, as usual, the long terminal alkyl chain completes the amphiphilic molecule in the capacity of hydrophobic unit. 

---