Irradiation solvent resistance

When BF3 is produced in this fashion in an epoxy resin, it catalyzes the cationic polymerization of the resin as discussed earlier. Typically, a small amount of the diazonium compound is dissolved in the epoxy coating formulation and irradiated with UV light to form thin films (0.5 to 1 mil) deposited on metal, wood, or paper substrates. The high reactivity of the BF3 type cure makes it possible to prepare hard solvent-resistant coatings in a few seconds exposure time under a standard 200-W/in. mercury vapor lamp. 

The most innovative photohalogenation technology developed in the latter twentieth century is that for purposes of photochlorination of poly(vinyl chloride) (PVC). More highly chlorinated products of improved thermal stabiUty, fire resistance, and rigidity are obtained. In production, the stepwise chlorination may be effected in Hquid chlorine which serves both as solvent for the polymer and reagent (46). A soHd-state process has also been devised in which a bed of microparticulate PVC is fluidized with CI2 gas and simultaneously irradiated (47). In both cases the reaction proceeds, counterintuitively, to introduce Cl exclusively at unchlorinated carbon atoms on the polymer backbone. 

For a positive resist, the film thickness of the irradiated region after development decreases until eventually a critical dose Dp is reached which results in complete removal of the film 8,9). The sensitivity and contrast (7p) are evaluated in a manner similar to that for a negative resist. After they have been spin-coated and prebaked, a series of pads of known area are exposed to varying doses. The substrate is developed in a solvent that does not attack the unexposed film and the thickness of the film remaining in the exposed areas measured. The film thickness is normalized to the original thickness, and this value is plotted as function of log dose, as shown in Figure 5 where Dp represents the sensitivity of the positive resist. Contrast (7p) is determined from the extrapolated slope of the linear portion of the response curve as... 

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 ... 

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