α‐Aminocaprolactam is reacted with the isocyanate function of 2‐isocyanatoethyl (meth)acrylate to yield monomers 2‐[3‐(2‐oxoazepin‐3‐yl)ureido]ethyl (meth)acrylate. These hydrogen bond‐forming monomers crystallize easily in macroscopic bunches of needles. Subsequently, homopolymers and copolymers of the monomers with N,N‐dimethylacrylamide are synthesized radically. The homopolymers have spherical structures and are semi‐crystalline showing large amorphous domains. Polymeric solutions of the homopolymers in water–ethanol have an upper critical solution temperature. In contrast, the solutions of the copolymers in water have a lower critical solution temperature. If copolymerized in concentrated solution, the copolymers show gelation after treatment with excess water. © 2014 Society of Chemical Industry