Structure-property relationships for cyanurate-containing, full interpenetrating polymer networks

Full sequential interpenetrating polymer networks (seq-IPN) of cross-linked polyurethane (CPU) and heterocyclic polymer networks (HPN) based on therma lly cured dicyanic ether of Bisphenol A (DCE) were characterized by small-a ngle X-ray diffraction, dynamic mechanical analysis, stretching calorimetry and microhardness measurements. Neat CPU was shown to be a microphase-sepa rated system characterized by a regular, three-dimensional macrolattice of network junctions, embedded in uniform-size microdomains of stiff chain fra gments which spanned the continuous matrix of soft chain fragments. In cont rast, no large-scale structural heterogeneities were detected in the HPN. T he X-ray long spacing (L), the degree of microphase segregation (DMS), the cu-relaxation temperature and the mechanical properties (elastic modulus an d microhardness) were studied as a function of HPN content. Results are exp lained in the light of a model that discusses the maximum degree of CPV swe lling by molten DCE as a function of composition. It is suggested that pred ominantly chemical interactions between the molten DCE and the stiff chain fragment microdomains, reinforcing primary physical interactions, are respo nsible for the observed transition at 40% HPN content to a more homogeneous phase morphology of seq-IPNS. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.