The nanostructure and dynamics over the temperature range of -140 to 300 degrees C were studied in a series of polycyanurate (PCN)-poly(tetramethylene glycol) (PTMG) hybrid networks by wide-angle X-ray diffraction and small-angle X-ray scattering, with a synchrotron radiation setup, and by differential scanning calorimetry (DSC) and laser-interferometric creep rate spectroscopy (CRS) techniques, respectively. The networks were synthesized from the dicyanate ester of bisphenol A and hydroxyl-terminated PTMG with a number-average molecular weight of 1.000 g/mol; the PTMG content varied from 0 to 40 wt %, and the degree of its chemical incorporation into the PCN network changed from 78.8 to 97%. The noncrystalline structure and considerable structural nanoheterogeneity of the hybrid networks were shown. CRS/DSC analysis revealed a complicated dynamic behavior, that is, a wide dispersion of glass transitions in the hybrid networks due to the presence of nanodomains with different degrees of rigid crosslinking (i.e., compositional nanoheterogeneity). Besides the physical significance, the plurality of glass transitions found in the PCN-PTMG hybrid networks was also of practical interest because it resulted in increasing mechanical strength of the brittle PCN network due to microplasticity arising at room temperature and moderate temperatures and the retention of some rigidity and creep resistance at temperatures much higher than the basic glass-transition temperature. (c) 2005 Wiley Periodicals, Inc.