Novel thermosetting systems based on cyanate ester resins (CERs) have been created through the polycyclotrimerization reaction of dicyanate ester of bisphenol E (DCBE) in the presence of different amounts of 1-heptyl pyridinium tetrafluoroborate [HPyr][BF4] Ionic Liquid (IL). A significant accelerating effect on the curing kinetics of DCBE was found by FTIR analysis. The reaction mechanism for the [HPyr] [BF4]-catalyzed polycyclotrimerization of DCBE was newly proposed via the formation of a [CN](delta+) -[HPyr](delta-) complex as a key intermediate. Structure-properties relationships for the thermostable CER/ IL networks were investigated by using DSC, DMTA, dielectric spectroscopy, tensile testing, quasi-dc measurements (I-V characteristics), and TGA. All the nanocomposites showed excellent thermal stability up to 300 C-degrees, indicating the formation of a densely crosslinked network even at high IL content (40 wt %), and they could be used at high temperatures above their T-g without significant thermal degradation. Nanoscale phase separation led to the creation of ionic channels within the CER matrix to ensure photosensitivity properties. (C) 2018 Elsevier Ltd. All rights reserved.