Intermaterial dividing surfaces (IMDS) in strongly segregated block copolymer systems are typically of constant mean curvature (CMC). This observation largely derives from the interplay of the thermodynamics of chain deformation and interfacial tension. Recently, a compositionally symmetric, linear poly(2-vinylpyridine)-b-polyisoprene-b-polystyrene (P2VP-PI-PS) triblock copolymer with each block having a M-w similar to 15 000, was observed to order in a hexagonal lattice of P2VP cylinders, surrounded by a PI annulus within a PS matrix. The PI/PS IMDS was of non-CMC, assuming a pseudohexagonal cross section. This striking morphological behavior originates from the nonuniform degree of chain deformation occurring in the microstructure and indicates that the PI/PS IMDS is strongly coupled to the shape of the Wigner-Seitz cell of the microdomain lattice. We further probe this phenomenon by attempting to alter the curvature of the PI/PS interface through incorporation of homopolystyrene (h-PS) into the PS matrix by preparing P2VP-PI-PS/h-PS (PIS/S) blends having a composition of 90/10 (v/v) and (M-w)(h-PS) similar to 4000-100 000. Using TEM and SAXS, we observe a transition in the PI/PS IMDS as a function of the molecular weight of h-PS. When (M-w)(h-PS) < 50 000, the tethered PS blocks behave as "wet brushes". In this regime, the non-CMC character of the PI/PS IMDS is preserved and a slight contraction in the domain spacing is observed due to a nearly uniform distribution of h-PS in the matrix. When (M-w)(h-PS) = 50 000, behavior characteristic of the "dry brush" regime is seen. The PI/PS IMIDS appears nearly circular in cross section with an accompanying increase in the domain spacing relative to that of the neat triblock. This behavior originates from a nonuniform distribution of h-PS in the matrix, with preferential segregation to the corners of the Wigner-Seitz cell. As the molecular weight of h-PS is further increased, the homopolymer is ejected from the microdomain structure and macrophase separates from the tethered PS blocks.