Macro-photoinitiators having defined polymer chain structure are provided. The macro-photoinitiators are terminated with residues of thiol and/or hydroxyl functional photoinitiators. The macro-photoinitiators may be prepared by controlled radical polymerization methods, such as atom transfer radical polymerization and single electron transfer polymerization methods. Also provided are curable (e.g., photocurable) compositions that include the macro-photoinitiators of the present invention.