Viscoelastic behavior of interpenetrating networks of polyurethane and polyurethane acrylate

Abstract

SynopsisThe temperature dependence of the dynamic viscoelastic behavior of interpenetrating networks (IPN) of polyurethane (PU) prepared from poly(oxypropylenedio1) (POP) and toluylene diisocyanate (TDI), and of polyurethane diacrylate (PUA) prepared from POP and TDI by reacting isocyanate groups of the prepolymer with 2-hydroxyethyl acrylate, was measured in the main transition region. The photoelastic behavior of IPN swollen in dimethylformamide (DMF) and methyl ethyl ketone (MEK) was examined in the rubbery region. The temperature dependences of the dynamic Young modulus E* of IPN in the concentration range of PUA 3 50 vol.% indicate a pronounced two-phase behavior. The effect of the composition of IPN on the temperature dependence of the modulus E* was quantitatively described by Takayanagi's two-phase model with the conclusion that the PU network is the continuous phase of IPN at I 90% PUA. While in the range of high concentrations of PUA ( 3 5%) the contributions of phases to E* are additive within the whole range of temperatures, the thermomechanical behavior at low PUA concentrations (640%) is more complex. T h i s finding is interpreted by the existence of an interfacial layer which leads to the loss of the distinct two-phase character of IPN. The higher number of elastically active network chains (EANC) of the PUA network compared with the PU network corresponds to different molecular weights of POP used in the preparation of both components. The nonadditive dependence both of the concentration of EANC and of the stress-optical coefficient on composition confirms the heterogeneous character of the IPN structure.

Use of SAXS to Characterize the Morphology of Poly(polyethylene glycol diacrylate)/Epoxy Resin Interpenetrating Networks

“…nical spectroscopy, as well as other experimental methods. 7,8 The main problems in IPN morphology centred around the shape and size of the phases and aspects of dual-phase continuity. In particular, theoretically derived equations were developed to predict the domain size as a function of composition.9h12 Recently, small-angle neutron and X-ray scattering (SANS and SAXS, respectively) have been applied to the study of the morphological features of IPNs.13h15 The development of microheterogenous regions, as well as periodic or modulated structures in hybrid matrices, points to the role played by interphase interaction and interphase layers inÑuencing the properties of these systems.…”

Phase-Separated Interpenetrating Polymer Networks

“…Dotted curve calculated by Eqs. 124-127 for model of homogeneous mixture (E * = 0.5 (E * PU + E * PUA )) with the composition PU/PUA = 1 : 1 assuming that PU is the continuous phase [184] phase forms a continuous medium up to 90 vol % of the PUA network. Such a conclusion agrees with the data of electron microscopy.…”

“…The Takayanagi model allows calculation of the value of the complex modulus E * . In [184] the methods of calculating E and E * were proposed. For this purpose, using the parameters of the Takayanagi model, the following set of equations was derived:…”

“…At the same time, the increase in the segregation degree leads to the decrease in the thickness and the fraction of an interphase. A theoretical estimate of the influence of an interphase on the viscoelastic characteristics of IPNs and similar systems may be given on the basis of a model of the Takayanagi type [184,238,239].…”

“…This shortcoming is absent in the case of a three-phase model, presented in Fig. 42 [184]. The modulus of the three-phase model E * may be calculated as follows:…”