Developing solvents

Fig. 24. Representative cross-linking systems employed in negative tone CA resists, (a) Epoxy polymers requiring organic solvent development, (b) PHOST-based cross-linking systems requiring aqueous development, (c) Monomeric cross-linking agents used in PHOST matrix polymers.

In studies in Denmark in the 1920s, Henrik Dam noticed that chicks fed a diet extracted with nonpolar solvents developed hemorrhages. Moreover, blood taken from such animals clotted slowly. Further studies by Dam led him to conclude in 1935 that the antihemorrhage factor was a new fat-soluble vitamin, which he called vitamin K (from koagulering, the Danish word for coagulation ). 

Water-soluble polymeric dyes have been prepared from water-insoluble chromophores, viz., anthraquinone derivatives. Unreacted chromophore and its simple derivatives, which are all water-insoluble, remain in solution due to solubilization by the polymeric dye. A method has been developed to separate and quantitate the polymeric dye and these hydrophobic impurities using Sephadex column packing. The solvent developed has the property of debinding the impiirities from the polymer, and further allows a separation of the imp irities into discrete species. This latter separation is based on the functional groups on the impurity molecules, having a different interaction with the Sephadex surface in the presence of this solvent. The polymer elutes at the void volume... 

BCD [Base-Catalyzed Decomposition] A process for decomposing hazardous organochlorine compounds by treating them in oil at 300 to 350°C with sucrose and a high-boiling solvent. Developed by the U.S. Environmental Protection Agency in 1991. 

Butex A process for separating the radioactive components of spent nuclear fuel by solvent extraction from nitric acid solution, using diethylene glycol dibutyl ether (also called Butex, or dibutyl carbitol) as the solvent. Developed by the Ministry of Supply (later the UK Atomic Energy Authority) in the late 1940s. Operated at Windscale from 1952 until 1964 when it was superseded by the Purex process. 

Cansolv A "flue-gas desulfurization process based on the selective absorption of sulfur dioxide in certain amine-based organic solvents. Developed by Union Carbide Corporation the first plant was planned for startup at Newburgh, IN, in 1994. See HS. 

Dilchill [Dilute, chill] A process for dewaxing petroleum by controlled crystallization, with cooling accomplished by the incremental addition of a cold solvent. Developed by Exxon Research Engineering Company. 

Rectiflow A multi-stage, liquid-liquid extraction process for removing non-paraffinic components from lubricating oils. Furfural has been used as the solvent. Developed and used by the Shell Petroleum Company in the 1940s, subsequently abandoned. 

Sepasolv MPE [Methyl isopropyl ester] A variation on the Selexol process, using the methyl isopropyl ethers of polyethylene glycol as the solvent. Developed by BASF. Four commercial plants were operating in 1985, removing hydrogen sulfide from natural gas. Wolfer, W., Hydrocarbon Process., 1982,61(11), 193. 

UNICARB [Union Carbide carbon dioxide] A process for spray painting objects using supercritical carbon dioxide as the solvent. Developed by Union Carbide Company and workers at Johns Hopkins University. 

In many cases the solvent was observed to have a large effect on the optical purity of the product. Examples of this, with a ketone and the rhodium cp TsDPEN catalyst, are shown in Table 35.3. Further optimization of this reaction improved the enantiomeric excess to 98%. A second example involved the reduction of 4-fluoroacetophenone in this case the enantioselectivity was largely unaffected, but the rate of reduction changed markedly with solvent. Development of this process improved the optical purity to 98.5% ee. 

It was indicated earlier that swelling limits resolution in solvent-developed negative resists. It was also intimated that swelling effects could be minimized if there were a sufficient polarity change between the exposed and non-exposed areas of the type mentioned in the previous discussion of the PBOCST system. A similar principle was utilized by Hofer et al., (145-146) at IBM, based on ion pair formation. The resist consists of a polystyrene polymer to which tetrathiofulvalene (TTF) units have been attached. When spun down with an acceptor such as CBr4, a complex is formed which, on irradiation, undergoes an electron transfer reaction to form an ion pair ... 

The kinetics of the laser-induced polymerization was followed either by measuring the thickness of the insoluble polymer film formed on the quartz plate after laser exposure and solvent development, using UV spectroscopy or by monitoring the decrease of the IR absorption of the coating at 810 cm-1 which corresponds to the twisting vibration of the acrylate CH2=CH double bond. This last method permits accurate evaluation of the rate of polymerization (Rp) by observing the variation of the 810 cm-1 band, and using Equation 2 ... 

Draw a picture in your notebook of the polyamide thin-layer plate exposed under UV light after each of the two or three solvent developments. These pictures should look similar to Figure E2.7. Three fluorescent areas should be evident after solvent 2 however, better separation is achieved by solvent 3. A blue fluorescent area at the bottom of the plate is dansic acid (DNS-OH), which is a hydrolysis product of dansyl chloride. A blue-green fluorescent spot about one-third to one-half up the plate is dansyl amide (DNS-NH2), which is produced by reaction of dansyl chloride with ammonia. A third spot, which usually fluoresces green, is the dansyl derivative of the NH2-terminus amino acid. Note the positions of the standard dansyl amino acids and compare with the unknown. What is the identity of the NH2-terminal amino acid Are any other fluorescent spots evident on the plate Using polarity or nonpolarity, try to explain the position of each molecule on the thin-layer plate. 

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