With benzophenone as photoinitiator

a two-step vapor-phasc photografting of AA in LDPE film has been studied mechanically The diffusion of BP into LDPE film has been carried out by dipping LDPE film into BP acetone solution for various periods of time and monitoring the concentrations in the film bvmeasuring its absorption at 254nm on a 756-MC spectrophotometer．The diffusion coefficient

whichdecreased with the increasing of the concentration of BP

Was between 0．8～2．0 X 10-12m2·sec-1．This monitoring method was also used in the study of the photoreducrion of BP．The results showed that

when far UV(λG) increased quickly at first

and then leveled up．while the far UV was filtered

G became lower at the beginning of the reaction than that while it WaS radiated by UV directly．but about 5 min later

there was little difference．Raising temperature could increase the percent of graft remarkably．Furthermore．the grafting system showed some living polymerization character：The graft yield increased continually even BP has bean used up

which can be interpreted by the re-cleavage of the weak bond formed by LDPE chain and semipinacol radicals．Based on these facts

a monomer diffusion controlling principle

which Was thought the main factor affecting the graft yield was discussed．