group at the upper limit the organosiloxane units can all contain a group possessing the benzophenone derivative structure nevertheless if the number of the groups possessing the benzophenone derivative structure is too low sensitization will be insufficient if the number is too high the miscibility with photosensitive resins especially with photosensitive silicone resins and photosensitive organopolysiloxanes will decrease therefore it is preferable to have this group present at 0 2 to 50 of the total number of organic groups r 4 q in each molecule a preferred embodiment of the present invention is an organopolysiloxane photosensitizer wherein all r 4 groups are methyl groups the resulting methyl containing photosensitizers are particularly useful in the methyl silicone photocurable resins delineated below a particularly useful embodiment of the present invention is the fluid organopolysiloxane photosensitizers illustrated by the examples disclosed below and encompassed by the general formula r 3 4 sio r 2 4 sio x r 4 hsio y r 4 qsio z sir 3 4 herein r 4 and q are as delineated above preferably ch 3 and str8 respectively and x y and z have average values such that their sum is less than 1000 and z is at least 1 the values of x and y can both be zero.