Effect of chemical clusters on photoelastic behaviour and small-angle X-ray scattering of epoxide networks based on poly(oxypropylene)diamines

Viscoelastic and equilibrium photoelastic behaviour and small-angle X-ray s cattering of epoxide networks based on bisphenol A diglycidyl ether (DGEBA) and two poly(oxypropylene)diamines (Jeffamine(R) D-400 and D-2000) were in vestigated. Networks were prepared with the stoichiometric ratio of amine h ydrogens and epoxy (E) groups (r(H) = 2[NH2]/[E] = 1) with various composit ions of(D-400 + D-2000)/DGEBA; seven networks with the weight ratios of D-4 00/D-2000 = 1/0, 0.83/0.17, 0.67/0.33, 0.5/0.5, 0.33/0.67, 0.17/0.83 and 0/ 1 were prepared. Time-temperature superposition was applied to photoelastic data. With increasing content of long D-2000 diamine, the superimposed pho toelastic functions at the reference temperature T-r = 0 degrees C are shif ted to shorter reduced times t/a(T, T-r) (a(T, T-r) is the horizontal shift factor) by similar to 18 decades. Although mechanical and optical shift fa ctors, log a(T, T-r), of two-component networks are virtually the same and their temperature dependences can be described by the WLF equation, these f actors for three-component networks are different and cannot be described b y the WLF equation. As expected, the equilibrium modulus decreases with inc reasing contents of D-2000 diamine in networks. On the contrary, the equili brium stress-optical coefficient C-e passes through a maximum at the weight fraction of DGEBA in networks, w(E) approximate to 0.50. SAXS experiments show a non-homogeneous distribution of DGEBA segments in three-component ne tworks; the deviations from homogeneous distribution reach a maximum for ne tworks with w(E) approximate to 0.50. All data suggest that in three-compon ent networks, chemical clusters formed by sequences with non-random partici pation of short and long diamines exist and that optical functions are more sensitive to these chemical heterogeneities than mechanical modulus. In ad dition, a modification of photoelastic apparatus for automatic measurement of the strain-birefringence was suggested. (C) 2000 Elsevier Science Ltd. A ll rights reserved.