REACTION MECHANISM OF BENZOPHENONE -PHOTOINITIATED CROSSLINKING OF POLYETHYLENE

【摘要】 <正> The radical intermediates, the crosslink microstructures, and the reaction mechanism of benzophenone （BP）-photoinitiated crosslinking of low-density polyethylene （LDPE） and model compounds （MD） have been reviewed in detail.The spin-trapping electron spin resonance （ESR） spectra obtained from the LDPE/BP systems with spin-trap agents showthat two kinds of polymer radical intermediates are mainly formed: tertiary carbon and secondary carbon radicals. The spin-trapping ESR studies of MD/BP systems give further evidence that photocrosslinking reactions of PE predominantly takeplace at sites of tertiary carbon, secondary carbon, and especially allylic carbon when available. The high resolution ¹³C-NMR spectra obtained from LDPE and MD systems show that the crosslink microstructures have H- and Y-type links andthat their concentrations are of the same order. The fluorescence, ESR ¹³C and ¹H-NMR spectra from the PE and MDsystems demonstrate that the main photoreduction product of BP（PPB） is benzpinacol formed by the recombination of twodiphenylhydroxymethyl （K·） radical intermediates. Two new PPB products: an isomer of benzpinacol with quinoid structure,1-phenylhydroxymethylene-4-diphenylhydroxymethyl-2, 5-cyclohexadiene and three kinds of α-alkyl-benzhydrols have beendetected and identified. These results provide new experimental evidence for elucidating the reaction mechanism in the BP-photoinitiated crosslinking of polyethylene.更多还原

【Abstract】 The radical intermediates, the crosslink microstructures, and the reaction mechanism of benzophenone （BP）-photoinitiated crosslinking of low-density polyethylene （LDPE） and model compounds （MD） have been reviewed in detail.The spin-trapping electron spin resonance （ESR） spectra obtained from the LDPE/BP systems with spin-trap agents showthat two kinds of polymer radical intermediates are mainly formed: tertiary carbon and secondary carbon radicals. The spin-trapping ESR studies of MD/BP systems give further evidence that photocrosslinking reactions of PE predominantly takeplace at sites of tertiary carbon, secondary carbon, and especially allylic carbon when available. The high resolution ¹³C-NMR spectra obtained from LDPE and MD systems show that the crosslink microstructures have H- and Y-type links andthat their concentrations are of the same order. The fluorescence, ESR ¹³C and ¹H-NMR spectra from the PE and MDsystems demonstrate that the main photoreduction product of BP（PPB） is benzpinacol formed by the recombination of twodiphenylhydroxymethyl （K·） radical intermediates. Two new PPB products: an isomer of benzpinacol with quinoid structure,1-phenylhydroxymethylene-4-diphenylhydroxymethyl-2, 5-cyclohexadiene and three kinds of α-alkyl-benzhydrols have beendetected and identified. These results provide new experimental evidence for elucidating the reaction mechanism in the BP-photoinitiated crosslinking of polyethylene.更多还原