







Block copolymers comprising chemically distinct polymers linked together are intriguing, because microphase separations of block copolymer melts provide superb periodic morphologies: lamellar, bicontinuous, cylindrical and spherical phases. A common feature in these morphologies, which is not usually mentioned, is that at least one component occupying large blocks of copolymers is unbounded in space, such as a matrix in a spherical or a cylindrical phase. Using Monte Carlo simulations, we show that a cellular and periodic morphology appears in microphase separations of symmetric "ABCD" starblock copolymer melts. In the structure, all components form spatially bounded cellular domains. Because periodic elements are cells instead of atoms, we refer to the structure as a "cell crystal'' and the phase as a "cell (crystalline) phase," whose lattice constant is nanoscale of the order of 10100 nm, the domain sizes of microphase separations. 







