Here we report the phase behavior of a family of montmorillonite (MMT) block copolymer brushes (MBBs), a novel class of polymer nanocomposites. MBBs are comprised of discrete MMT platelets encapsulated with block copolymer brushes. These MBBs were synthesized via surface-initiated atom transfer radical polymerization using halogenated alkylammonium surfactants to localize initiation sites on the clay surfaces. Two styreninc MBB systems-poly(styrene-b-n-butyl acrylate) and poly(styrene-b-t-butyl acrylate)-were prepared varying the composition and total <(M)overbar>(n) = 80-250 kDa. MBB materials were compared with their non-clay bulk block copolymer counterparts via electron microscopy and a host of mechanical tests in both the solid and melt states. Notably, MBBs have similar melt-state rheological properties compared to neat block copolymers and are thus amenable to current processing techniques. MBBs were found to self-assemble into single grain morphologies across incredibly large areas (>3 mu m) which resulted in extremely well-ordered, defect-free lamellar structures with applications in microelectronics. (C) 2015 Wiley Periodicals, Inc.