A photoactive additive formed from the reaction of: (i) a benzophenone having the structure of Formula,, or: wherein R and R' are independently alkyl, aryl, alkenyl, halogen, sulfonate, phosphate, phosphonate, nitrile, thiophene, or pyrrole; p is an integer from 0 to 5; q and r are independently an integer from 0 to 4; s is an integer from 0 to 3; L is alkylene, arylene, alkenylene, substituted alkylene, substituted arylene, substituted alkenylene, or amino, preferably L is an oxyalkylene; and Y is hydroxyl, alkoxy, aryloxy, or halogen; or an anhydride thereof; and (ii) a first linker moiety comprising a plurality of functional groups and having the structure of one of the following Fomulas, and -: wherein R a and R b each represent a halogen atom or a monovalent hydrocarbon group and may be the same or different; p and q are each independently integers of 0 to 4; and A represents one of the groups of formula (B-1): wherein R c and R d each independently represent a hydrogen atom or a monovalent linear or cyclic hydrocarbon group and R e is a divalent hydrocarbon group; wherein each R k is independently a C 1-10 hydrocarbon group, and n is 0 to 4; wherein each X is independently hydrogen, halogen, or alkyl; and j is an integer from 1 to 20; wherein R 13 and R 15 are each independently a halogen or a C 1 -C 6 alkyl group, R 14 is a C 1 -C 6 alkyl, phenyl, or phenyl substituted with up to five halogens or C 1 -C 6 alkyl groups, and c is 0 to 4; wherein R 1 represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aryl-substituted alkenyl group having 7 to 13 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms; R 2 represents a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aryl-substituted alkenyl group having 7 to 13 carbon atoms, or a fluoroalkyl group having 1 to 12 carbon atoms; m represents an integer of 0 to 4; and n represents an integer of 0 to 14; wherein R 1 to R 4 are each independently a hydrogen atom, a hydrocarbon group with 1 to 9 carbon atoms which may contain an aromatic group, or a halogen atom; or wherein R 1 is an isosorbide unit and R 2 -R 9 are each independently a hydrogen, a halogen, a C 1 -C 6 alkyl, a methoxy, an ethoxy, or an alkyl ester; and (iii) a difunctional chain extender has the structure of one of the where Y is hydroxyl, halogen, alkoxy, or aryloxy; and where n is 1 to 20. (i) a benzophenone having the structure of Formula,, or: wherein R and R' are independently alkyl, aryl, alkenyl, halogen, sulfonate, phosphate, phosphonate, nitrile, thiophene, or pyrrole; p is an integer from 0 to 5; q and r are independently an integer from 0 to 4; s is an integer from 0 to 3; L is alkylene, arylene, alkenylene, substituted alkylene, substituted arylene, substituted alkenylene, or amino, preferably L is an oxyalkylene; and Y is hydroxyl, alkoxy, aryloxy, or halogen; or an anhydride thereof; and (ii) a first linker moiety comprising a plurality of functional groups and having the structure of one of the following Fomulas, and -: wherein R a and R b each represent a halogen atom or a monovalent hydrocarbon group and may be the same or different; p and q are each independently integers of 0 to 4; and A represents one of the groups of formula (B-1): wherein R c and R d each independently represent a hydrogen atom or a monovalent linear or cyclic hydrocarbon group and R e is a divalent hydrocarbon group; wherein each R k is independently a C 1-10 hydrocarbon group, and n is 0 to 4; wherein each X is independently hydrogen, halogen, or alkyl; and j is an integer from 1 to 20; wherein R 13 and R 15 are each independently a halogen or a C 1 -C 6 alkyl group, R 14 is a C 1 -C 6 alkyl, phenyl, or phenyl substituted with up to five halogens or C 1 -C 6 alkyl groups, and c is 0 to 4; wherein R 1 represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aryl-substituted alkenyl group having 7 to 13 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms; R 2 represents a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aryl-substituted alkenyl group having 7 to 13 carbon atoms, or a fluoroalkyl group having 1 to 12 carbon atoms; m represents an integer of 0 to 4; and n represents an integer of 0 to 14; wherein R 1 to R 4 are each independently a hydrogen atom, a hydrocarbon group with 1 to 9 carbon atoms which may contain an aromatic group, or a halogen atom; or wherein R 1 is an isosorbide unit and R 2 -R 9 are each independently a hydrogen, a halogen, a C 1 -C 6 alkyl, a methoxy, an ethoxy, or an alkyl ester; and (iii) a difunctional chain extender has the structure of one of the where Y is hydroxyl, halogen, alkoxy, or aryloxy; and where n is 1 to 20.