No abstract

Macromolecular antioxidants with highly suppressed leaching to the environment, based on hyperbranched poly(ethyleneimine) carrier with bonded sterically hindered phenol and 2 alkyl compatibilizing groups with various chain length were synthesized and tested for their efficiency in stabilization of polyolefins. The synthesis of the macromolecular antioxidants was carried out by amidation of the amine groups present in poly(ethyleneimine) with various carboxylic acids containing sterically hindered phenol and compatibilizing groups, such as n-butyryl, lauryl or stearyl. The structure of the resulting polymers was analyzed by 1 H NMR and by GPC. The antioxidant content of the samples was determined by UV-Vis spectroscopy. The efficiency of the synthesized antioxidants in thermooxidative stabilization of polypropylene was determined by chemiluminescence. The efficiency in photostabilization of polypropylene and polyethylene was investigated by using FT IR and UV-Vis spectroscopies. It was found that the macromolecular antioxidant which did not contain any compatibilizing groups shows the best stabilizing efficiency in both thermooxidative and photooxidation tests. The extent of extraction of the synthesized macromolecular antioxidants from polypropylene films was investigated as well. Low extent of extraction of the maromolecular antioxidants from the polypropylene films was observed in contrast to the high level of leaching of commercially used low molecular weight phenolic antioxidant. These results indicate the environmental advantage of the investigated poly(ethyleneimine) based macromolecular antioxidants over the widely applied low molecular weight compounds.

Peroxyl radicals generated as a result of y-irradiation of isotactic and atactic polypropylene and high-density polyethylene have been identified and quantified by a combination of electron spin resonance (ESR) and derivitization infrared spectroscopies. When samples are maintained a t 5-60 "C, peroxyl radicals are indefinitely stable in polyolefins yet react smoothly with nitric oxide to give nitrates. From infrared spectroscopy it is possible to identify the structure of some of these nitrates (primary, secondary, or tertiary) and hence the structure of the peroxyl radicals that are the origin of all oxidative chains in the polymers.Good agreement was found between total peroxyl species measured by ESR and the total level of nitrate products from infrared. From polyethylene, the dominant peroxyl species is proposed to be -CH&H(02')-CHz-, whereas in the polypropylenes the secondary peroxyl dominated over the tertiary species. This dominance is very different from that expected from peroxyl radical selectivity for attack on polymer CH groups in the subsequent propagation reactions.