Structure-microhardness relationship in semi-interpenetrating polymer networks

Two series of single-phase, semi-interpenetrating polymer networks (semi-IPNs) based on the same linear polyurethane (LPU) and two different heterocyclic polymer networks (HPNs), respectively, were characterized by the room temperature microhardness H measurement. It is shown that the H value linearly increases with both the mass content of the stiffer component (HPN) and the glass transition temperature of a semi-IPN. The latter dependence can be justified on the assumption that the excess enthalpy of the glass with respect to a hypothetical melt state is a measure of the yield strength of the glassy quasi lattice.This work was supported by the DGICYT, Spain (grant PB94-0049). V. P. P. thanks the Ministerio de Educacion y Cultura, Spain, for the award of a sabbatical grant

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

9 pags, 11 figs, 1 tabsFull sequential interpenetrating polymer networks (seq-IPN) of cross-linked polyurethane (CPU) and heterocyclic polymer networks (HPN) based on thermally cured dicyanic ether of Bisphenol A (DCE) were characterized by small-angle X-ray diffraction, dynamic mechanical analysis, stretching calorimetry and microhardness measurements. Neat CPU was shown to be a microphase-separated system characterized by a regular, three-dimensional macrolattice of network junctions, embedded in uniform-size microdomains of stiff chain fragments which spanned the continuous matrix of soft chain fragments. In contrast, no large-scale structural heterogeneities were detected in the HPN. The X-ray long spacing (L), the degree of microphase segregation (DMS), the α-relaxation temperature and the mechanical properties (elastic modulus and microhardness) were studied as a function of HPN content. Results are explained in the light of a model that discusses the maximum degree of CPV swelling by molten DCE as a function of composition. It is suggested that predominantly chemical interactions between the molten DCE and the stiff chain fragment microdomains, reinforcing primary physical interactions, are responsible 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. | Full sequential interpenetrating polymer networks (seq-IPN) of cross-linked polyurethane (CPU) and heterocyclic polymer networks (HPN) based on thermally cured dicyanic ether of Bisphenol A (DCE) were characterized by small-angle X-ray diffraction, dynamic mechanical analysis, stretching calorimetry and microhardness measurements. Neat CPU was shown to be a microphase-separated system characterized by a regular, three-dimensional macrolattice of network junctions, embedded in uniform-size microdomains of stiff chain fragments which spanned the continuous matrix of soft chain fragments. In contrast, no large-scale structural heterogeneities were detected in the HPN. The X-ray long spacing (L), the degree of microphase segregation (DMS), the α-relaxation temperature and the mechanical properties (elastic modulus and microhardness) were studied as a function of HPN content. Results are explained in the light of a model that discusses the maximum degree of CPV swelling by molten DCE as a function of composition. It is suggested that predominantly chemical interactions between the molten DCE and the stiff chain fragment microdomains, reinforcing primary physical interactions, are responsible for the observed transition at 40% HPN content to a more homogeneous phase morphology of seq-IPNS.This work was supported by the DGICYT, Spain (GrantPB94-0049), and by the project INTAS-97-1936. Thanksare due to the Ministerio de Educacion y Cultura, Spain, for a sabbatical grant to V.P.