A triple hydrogen bonding interaction effectively controlled the stereochemistry during radical polymerization of acylamide derivatives. An acrylamide monomer, in which amide ( proton donor site, D) and pyridine ( proton acceptor site, A) moieties were arrayed in the DAD sequence, was polymerized in the presence of a cyclic imide as the ADA-type receptor in CHCl3 to give syndiotactic polymers (r = 72%) even at 60 degrees C while atactic polymers (r = 43%) were obtained without the mediator. Furthermore, the simultaneous control of the tacticity and the molecular weights of the polymers were attained by RAFT polymerization in the presence of the mediator.