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 2-15 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 (https://doi.org/10.1351/pac200476111985)