| Abstrakt: | SUMMARIES. The tendency to crosslink under near-ultraviolet and visible radiation has been demonstrated in polymers prepared from the n-propyl, n-butyl and isobutyl, n-amyl and isoamyl methacrylate esters, particularly in those with alkyl groups that contain tertiary hydrogens. The ratio of chain breaking to crosslinking has been shown to vary with temperature, the higher temperature favoring an increase in the tendency to crosslink. A number of toluene-soluble polymers have been found that exhibit little tendency to crosslink under the near-ultraviolet. Moreover, for those methacrylate polymers that do tend to crosslink, inhibitor systems can be used to delay the onset of insolubility as much as 15-fold. We have determined that the reciprocity law (intensity of illumination times induction time) essentially holds true over a 3o-fold range of intensity. Further, the rate of formation of insoluble matter has been shown to increase logarithmically with the decrease in the lowest wavelength of irradiance in the range of 400 to 300 nm. Crosslinking of these polymers can take place under the normal conditions of daylight or fluorescent-lamp illumination encountered in a museum, although at an extremely low rate. |
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