ABSTRACT
During my work using GPC-UV/VIS to analyze discolored polymers I have encountered four different situations, i.e., where the chromophores are located: (i) on the chain-ends, (ii) random and in all chains, (iii) in crosslinks between chains, or (iv) in small molecules. These four situations result in GPC-UV/VIS plots shown in Figures 1-4, respectively. Notice that in Figure I the region of the 3D plot where the chromophore is located (350-400 nm) is offset to the low MW side of the wavelength that the polymer backbone strongly absorbs (260 nm). This occurs because the chromophore is located on the chain-ends and the concentration of chain-ends, relative to the rest of the polymer backbone, increases as the MW decreases. In Figure 2, the chromophore (350-400 nm) and polymer backbone (260 nm) regions align almost perfectly. This shows that the chromophore is pendant and present in all polymer chains independent of MW. Figure 3 represents the least common situation, i.e., chromophores are concentrated in high MW chains. An example of how this could occur is the formation of chromophoric branches or crosslinks between chains. Finally, Figure 4 clearly shows that the chromophores are located only in low molecular weight molecules since the visible wavelength materials elute at a much longer retention time (18 min) than the polymer (12-14 min). Since the calibration curve for the GPC column is known (Figure 5), the approximate MW of the colored molecules can be determined.
