Poly(p-phenylene ether) (PPE) grafted with high-density polyethylene (HDPE), to form PPE-g-HDPE graft copolymers, were prepared by Friedel-Crafts alkylation of vinyl terminated HDPEs onto PPE. High and low molecular weight (MW) vinyl terminated HDPE precursors were synthesized by coordination insertion polymerization with organometallic catalysts that favor beta-hydride transfer. Both types of copolymers are highly effective compatibilizers for PPE/HDPE blends when PPE is the minor phase. The symmetric PPE-g-HDPE copolymer with high MW grafted HDPE shows a somewhat higher efficacy at reducing the dispersed phase size and delaying the onset of PPE phase continuity. However, when HDPE is the minor phase, the asymmetric PPE-g-HDPE copolymer with low-molecular-weight grafted HDPE appears to be more effective at reducing particle anisotropy and at delaying the HDPE phase continuity onset. This delay in HDPE phase continuity onset, in turn, allows the retention of high-temperature PPE stiffness in the blends with 20 wt% HDPE. An examination of the glass transition temperatures indicates that the symmetric copolymer with higher HDPE MW appears to have a marked tendency to form micelles within PPE and thus is less effective at modifying the HDPE/PPE interface when PPE is the matrix. (C) 2018 Elsevier Ltd. All rights reserved.