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 take place 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 and that their concentrations are of the same order.The fluorescence

ESR

13C and 1H-NMR spectra from the PE and MD systems demonstrate that the main photoreduction product of BP(PPB) is benzpinacol formed by the recombination of two diphenylhydroxymethyl(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 been detected and identified.These results provide new experimental evidence for elucidating the reaction mechanism in the BP-hotoinitiated crosslinking of polyethylene.