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

• Published in: European polymer journal 2000, Vol.36 (11), p.2327-2335
• Main Authors: Meloun, J., Krakovský, I., Nedbal, J., Ilavský, M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Epoxide networks; Equilibrium modulus; Exact sciences and technology; Organic polymers; Photoelasticity; Physicochemistry of polymers; Properties and characterization; Rheology and viscoelasticity; Stress-optical coefficient; Time-temperature superposition; X-ray scattering
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/S0014-3057(00)00013-6

Viscoelastic and equilibrium photoelastic behaviour and small-angle X-ray scattering of epoxide networks based on bisphenol A diglycidyl ether (DGEBA) and two poly(oxypropylene)diamines (Jeffamine ® D-400 and D-2000) were investigated. Networks were prepared with the stoichiometric ratio of amine hydrogens and epoxy (E) groups ( r H=2[NH 2]/[E]=1) with various compositions of (D-400 + D-2000)/DGEBA; seven networks with the weight ratios of D-400/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 photoelastic functions at the reference temperature T r=0°C are shifted to shorter reduced times t/a(T, T r ) (a(T, T r ) is the horizontal shift factor) by ∼18 decades. Although mechanical and optical shift factors, 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 factors for three-component networks are different and cannot be described by the WLF equation. As expected, the equilibrium modulus decreases with increasing contents of D-2000 diamine in networks. On the contrary, the equilibrium stress-optical coefficient C e passes through a maximum at the weight fraction of DGEBA in networks, w E≈0.50. SAXS experiments show a non-homogeneous distribution of DGEBA segments in three-component networks; the deviations from homogeneous distribution reach a maximum for networks with w E≈0.50. All data suggest that in three-component networks, chemical clusters formed by sequences with non-random participation of short and long diamines exist and that optical functions are more sensitive to these chemical heterogeneities than mechanical modulus. In addition, a modification of photoelastic apparatus for automatic measurement of the strain-birefringence was suggested.