hard-segment phase domain

Phase domain of microscopic or smaller size, usually in a block, graft, or segmented copolymer, comprising essentially those segments of the polymer that are rigid and capable of forming strong intermolecular interactions.
Hard-segment phase domains are typically of 215 nm linear size.
PAC, 2004, 76, 1985 (Definition of terms related to polymer blends, composites, and multiphase polymeric materials (IUPAC Recommendations 2004)) on page 2002