Surface functionalities, control methods

Arguably the most challenging aspect for the preparation of 1 was construction of the unsymmetrically substituted sec-sec chiral bis(trifluoromethyl)benzylic ether functionality with careful control of the relative and absolute stereochemistry [21], The original chemistry route to ether intermediate 18 involved an unselective etherification of chiral alcohol 10 with racemic imidate 17 and separation of a nearly 1 1 mixture of diastereomers, as shown in Scheme 7.3. Carbon-oxygen single bond forming reactions leading directly to chiral acyclic sec-sec ethers are particularly rare since known reactions are typically nonstereospecific. While notable exceptions have surfaced [22], each method provides ethers with particular substitution patterns which are not broadly applicable. 

Bromination. Bromination of polymer surface employing the bromoform plasma presents a highly selective method of controlled surface functionalization. Only traces of Br anions were detected as negligible side-products by means of XPS and, under adverse conditions, the deposition of polymer layers was observed as measured with a microbalance. The XPS measured introduction of Br at polymer surfaces for two types of plasma treatment is illustrated in Fig. 4. 

Unfortunately, current S3mthesis techniques, such as chemical vapor deposition, arc discharge, laser ablation, or detonation, typically lead to a mixture of various nanostructures, amorphous carbon, and catalyst particles rather than a particular nanostructure with defined properties, thus limiting the number of potential applications [1]. Even if pure materials were available, the size-dependence of most nanomaterial properties requires a high structural selectivity. In order to fully exploit the great potential of carbon nanostmctures, one needs to provide purification procedures that allow for a selective separation of carbon nanostructures, and methods which enable size control and surface functionalization. 

The selectivity of activated carbons for adsorption and catalysis is dependent upon their surface chemistry, as well as upon their pore size distribution. Normally, the adsorptive surface of activated carbons is approximately neutral, such that polar and ionic species are less readily adsorbed than organic molecules. For many applications it would be advantageous to be able to tailor the surface chemistry of activated carbons in order to improve their effectiveness. The approaches that have been taken to modify the type and distribution of surface functional groups have mostly involved the posttreatment of activated carbons or modification of the precursor composition, although the synthesis route and conditions can also be employed to control the properties of the end product. Posttreatment methods include heating in a controlled atmosphere and chemical reaction in the liquid or vapor phase. It has been shown that through appropriate chemical reaction, the surface can be rendered more acidic, basic, polar, or completely neutral [11]. However, chemical treatment can add considerably to the product cost. The chemical composition of the precursor also influences the surface chemistry and offers a potentially lower cost method for adjusting the properties of activated... 

Several laboratories have developed the methods of mesoporous silica surface functionalization with simultaneous removal of the surfactant and grafting of organic functionalities without prior calcination. A convenient and highly controllable approach to the surface functionalization of mesoporous silica[221] employs an alcoholic solution of... 

Seed functionalization These methods consist of the functionalization of a latex seed by a monomer or monomer mixture. This often permits surface incorporation to be increased, and is well adapted to formulating controlled charge density model colloids. 

The preparation of nylon-6,6 fabric containing N-chlorinated hydantoin functional groups which were covalently linked to the surface of the polyamide was outlined. The N-chlorinated hydantoin functional groups had biocidal activity against pathogenic microorganisms. Attenuated total reflectance FTIR spectroscopy studied showed that chlorination of the treated nylon-6,6 caused a blue shift of the hydantoin amide bands. This could be used as a quality control method to measure the degree of chlorination of the nylon-6,6 and hence, of the biocidal efficiency of the material. 25 refs. 

---