Nitroxide-functionalized polymers are attractive macroinitiators for nitroxide mediated polymerization (NMP) and further modification of polymers. In this work, a facile reaction method to chemically bond nitroxide groups to polymer chains has been demonstrated with incorporation of 2,2,6,6-tetramethylpiperydinyl-1-oxyl (TEMPO) groups into poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) through the atom transfer radical coupling reaction. The TEMPO-functionalized PPO (PPO-TEMPO) has been used as a macroinitiator for NMP of styrene to result in the corresponding PPO-g-PS graft copolymers. Moreover, PPO-TEMPO could be used to carry out a thermally-induced self-crosslinking reaction through radical coupling. The crosslinked PPO displays enhanced mechanical properties, reduced oxygen permeability coefficient (from 22.5 barrer to 3.5 barrer), low dielectric constant (2.40 at 10 GHz) and low dissipation factor (0.008 at 10 GHz), so as to have high potential for application in dielectric layers of microelectronics. (C) 2017 Elsevier Ltd. All rights reserved.