In this manuscript we report the crosslinking of pre-existing macromolecules in solution through the use of photoactive benzophenone chromophores. We show that a bifunctional crosslinker composed of two benzophenone chromophores as well as a single benzophenone chromophore crosslink poly (butadiene) and poly (ethylene oxide) in solution to form insoluble gels when irradiated with UV light. The molecular weight between crosslinks of the photo-generated gels was compared for the two crosslinkers, for an equivalent amount of benzophenone chromophores in each solution, by measuring the swelling ratio of the gels formed. Gels formed from the bifunctional benzophenone crosslinker were shown to contain more than twice as many crosslinks compared to gels formed from the crosslinker composed of a single benzophenone chromophore. EPR measurements of a nitroxide derivative absorbed into the gels further supported a higher crosslink density for the gels formed from the bifunctional benzophenone crosslinker. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 168-174, 2011