EPR power saturation techniques and spectral differentiation are used to isolate and simulate radical species in UHMWPE

In this study, we found that the linear growth with the square of the power of each radical species in X-irradiated ultra high molecular weight polyethylene (UHMWPE) has a different slope than the other radicals present. We used this fact to isolate radicals, which are known to be in the crystalline regions of polyethylene (alkyl) from the signals due to radicals in the amorphous regions (allyl, polyenyl, peroxyl). A process to eliminate oxidation of irradiated polyethylene was also studied and is discussed at the end. Recording of the radical's spectra was conducted at power settings as low as 10 μW and as high as 100 mW. Once the species were seen to be differentiated by using power saturation techniques (PST), various processing methods and spectral differentiation were used to verify the parameters used in performing simulations of selected spectra. The simulation parameters can be used to give a reasonable picture of the percentage of allyl, alkyl, peroxyl and polyenyl radicals present in UHMWPE EPR spectra. For example, simulation of a composite spectrum, obtained following the decay of the primary alkyl radicals, suggests the presence of allyl (n = 1), dienyl (n = 2), trienyl (n = 3) and polyenyl (n > 3) radicals (-C*-[CHCH-]n).