This paper reviews recent progress concerning polymeric self-assemblies in confined
spaces, including phase-separated structures of polymer blends and block copolymers.
Although a wide variety of polymer self-assemblies have been studied in terms of conventional
parameters, such as blend ratio, interaction of constituent polymers, block ratio,
and molecular weight, a series of unique structures appear when the systems are self-assembled
under confined conditions. Due to the limited space for phase separation, the polymers
in the confinement are frustrated, and the resulting morphologies are distinctly different
from those formed in free space. We give an overview of experimental and theoretical
studies of the frustrated morphologies. We begin by defining confinement with respect
to dimensionality and surface properties, and then introduce methods for producing
various shapes and sizes of three-dimensional confinement. Finally, we present morphological
and application-oriented studies and discuss the prospects for this research area.