Inhibition process, mixed solvents

The change from inhibition to acceleration of the rate of electrode reaction occurs exactly at the mixed solvent composition at which the process of reactant resolvation begins in the bulk of the solution. It appears that even partial resolvation of vanadium(III) ions (Avv(in)>0) initiates the increase of the rate of reaction in the surface phase, when the concentration of the organic solvent is considerably higher there than in the bulk. Such behavior is observed in mixtures of water with solvents of Lewis basicity lower (AN) and also higher (HMPA) than water. 

Free radical polymerization may be carried out in various media. Bulk polymerization is the simplest, but while the reactants (monomers) are most often liquid, the product (polymer) is solid. This leads to problems when removing the polymer from the reactor. In addition, since most free radical polymerizations are highly exothermic, the high viscosity of the monomer/polymer mix inhibits the removal of the heat of reaction. Solution polymerization will reduce, to some extent, the viscosity of the polymerizing mass, but it brings with it the environmental and health issues of organic solvents. In addition, the solvent reduces the monomer concentration, and hence the rate of polymerization. Finally, recovery and recycling of the solvent can add substantially to the cost of the process. Nevertheless, solution polymerization of vinylic monomers is used in a number of commercial processes. 

One problem associated with the PCM scheme is that during application of a photoresist such as AZI350J onto a PMMA film, a thin layer of PMMA is redissolved and mixed with the photoresist so that a thin interfacial layer is formed that remains after development of the photoresist layer and inhibits proper exposure and development of the PMMA layer. Because the PMMA developer, such as chlorobenzene or toluene, used in the capped process is chosen to be a nonsolvent for the photoresist, such a solvent cannot remove the interfacial layer. Therefore, some process, like plasma treatment, is required to remove the interfacial layer prior to the blanket exposure of the bottom PMMA layer (83, 85). 

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