Abstract: Amphiphilic random UV sensitive copolymers,poly(7-(4-vinylbenzyloxyl)-4-methylcoumarin-co- acrylic acid) P(VM-r-AA), were synthesized with various hydrophobic unit compositions. These polymers self-assembled into nano micelles in selective-solvent, which were used as polymeric particulate emulsifiers to stabilise the toluene-water interface.Experimentally, the more hydrophobic units the polymer contains, the more rigid the self-assembly micelles are, subsequently, the worse stability the emulsion stabilised by micelles exhibits. It is concluded that swelling polymer segments or chains played an important role in the emulsifying performance of the self assembly micelles, which further confirmed by the distinct discrepancy in the emulsifying performance of the P(VM-r-AA) micelles with PVM molar fraction 12% between the photo-cross-linked and not. Under alkaline condition, the cross linked micelles cann’t stabilise at the toluene water interface due to the restriction of the swelling polymeric chains, while stable toluene-in-water emulsions are stabilised by the uncross linked micelles.