prov:value
| - Linking groups used in the present compositions which are photochemically cleavable are represented by radicals of the formula: ##STR7## in which R1 is C1 -C8 alkyl, aryl or aralkyl; R2, R3 and R4 are each independently hydrogen, C1 -C8 alkyl, or C1 -C8 alkoxy; X21 is halogen, --SH, --SP, --OH, --NH2, --OP or --NHP, wherein P is a suitable protecting group; and q is an integer of from 1 to 10.
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