In this study, poly(arylene ether nitriles) containing pendant carboxyl groups (PEN-COOH) was first synthesized via nucleophilic aromatic substitution reaction from phenolphthalein, hydroquinone and 2,6-dicholorobenzonitrile. Then, poly(arylene ether nitriles) with pendant phthalonitrile groups (PEN-CN) was obtained via the Yamazaki-Higashi phosphorylation route from 4-(4-aminophenoxy)phthalonitrile (APN) with PEN-COOH in the presence of CaCl2, thus the phthalonitrile as pendant groups in PEN-CN were easily crosslinked by further thermal treatment. The effect of crosslinking density on the thermal stabilities, dielectric properties and water absorption of the PEN-CNs was investigated. These results showed that the T-g of PEN-CN was improved from 182 to 213 degrees C, dielectric constant (epsilon) was increased from 3.1 to 3.9, and dielectric loss (tan delta) was decreased from 0.090 to 0.013 at 1 kHz. The water absorption of PEN-CNs after thermal crosslinking was <1.01 wt %, which showed excellent water resisting property. Therefore, this kind of poly(arylene ether nitriles) containing pendant phthalonitrile could be a good candidate as matrix resins for high-performance polymeric materials. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 127: 1676-1682, 2013