Mechanical behavior of polycyanurate–polyurethane sequential full-interpenetrating polymer networks

Differential scanning calorimetry and dynamic mechanical spectroscopy studies have been performed between 120 and 600 K in a new series of sequential full-interpenetrating polymer networks (full-IPNs) of crosslinked polyurethane and polycyanurate network (PCN), based on dicyanate ester of 1,1'-bis-4,cyanatophenyl-ethane. The measurements have revealed the existence of two distinct glass transitions in the thermograms and of relaxation losses given by the overlap of two alpha(a)-relaxations in the mechanical spectra whose temperature locations change with changing weight ratio of polymeric component. These observations indicate that the morphology of this new class of full-IPNs is based on double-phase structures characterized by weak interchain interactions. The interpenetration affects markedly the glass transition temperatures revealed in the pure components as a consequence of modifications in the local environments of the relaxing molecular units in the two phases. Below the glass transition, two secondary relaxation losses have been observed which have been ascribed to local molecular transitions within each polymeric component. The analysis of their concentration behaviors leads to a conclusion that the interpenetration process affects markedly the local motion of the PCN component. (C) 2002 Elsevier Science B.V. All rights reserved.