The invention relates to radically copolymerizable acetophenone or benzophenone derivatives, which may be obtained by reacting a) acrylic or methacrylic compounds, which contain at least one isocyanate-reactive group [compounds a)], with b) compounds, which contain at least two isocyanate groups [compounds b)] and c) acetophenone or benzophenone derivatives, which contain at least one isocyanate-reactive group [compounds c)]. Said invention also relates to copolymers, which contain said copolymerizable photoinitiators, as well as to the use of said copolymers in UV-crosslinkable substances, in particular hot-melt pressure-sensitive adhesives.