Epoxy aromatic amines

Oleinik, E. F. Epoxy-Aromatic Amine Networks in the Classy State Structure and Properties. Vol. 80, pp. 49 — 99. 

Structure and Properties of Epoxy-Aromatic Amine Networks in the Glassy State... 

This paper will deal mainly with this type of polymers, focussing on the glassy state of epoxy-aromatic amine-cured polymers. However, many aspects of network glasses cannot be understood without considering the chemistry of their formation, degree of crosslinking, and behaviour in the rubbery state, which will be briefly referred to. 

Important Features of the Chemistry and Topology of Epoxy-Aromatic Amine Networks... 

In conclusion to the short analysis on curing chemistry of epoxy-aromatic amine networks (for more detailed analysis see papers of K. Dusek and B. Rozenberg in this volume), one can say that the chemical structure of the polymers under consideration is mainly determined by the curing reaction in Eq. (I). Equation II becomes important only for polymers with an excess of epoxy groups at T 150 °C. This rather simple situation makes the analyzed polymers very suitable for basic investigations. 

In our analysis and explanations of macro-properties of epoxy-aromatic amine networks, we mostly used the structural features which resulted from computer simulation 6 915 l9). In this section, we shall give a brief description of this model... 

The topological computer model of epoxy-aromatic amine networks showed the following very important structural characteristics of polymers ... 

The calculated equilibrium network moduli of elasticity and experimental moduli measured in the rubbery state10,34) of different epoxy-amine networks show quantitative agreement. This means that the real structural nonuniformity of cross-linked epoxy-aromatic amine polymers exists only at the level of statistical deviations of network structure from the ideal one. A comparison of Ecalc and E p is shown in Fig. 4. 

Figure 5 (a, b) shows typical heat capacities and thermal expansion coefficient curves for some epoxy-aromatic amine networks. Table 1 gives some numerical values for networks with different component ratios P Cp and P values for the glassy state do not practically depend on the chemical composition of networks and are very... 

Practically all OH groups are involved in H bonding in a bulk polymer19), since there are many proton acceptors available in epoxy-aromatic amine networks. At room temperature the concentration of free OH groups in networks is lower than 1-2%. The formation enthalpies of different H bonds in the networks measured by the shift of v(OH) vibrations in IR spectra are shown in Table 4. It is seen that the largest part of all H bonds ( 90% in a stoichiometric mixture) comes from the autoassociation of OH groups. 

Table 4. Enthalpies of formation of H bonds for epoxy-aromatic amine networks...

In Fig. 9 (a-c), TSD traces for some epoxy-aromatic amine networks in the glassy state are shown. It is clearly seen that in the glassy state there exist several different types, at least four, of TSD peaks (Fig. 9c). A special measurement has shown that all TSD peaks are a result of dipole relaxation but not of the migration of ions or heterocurrents. From Fig. 9 a and b it becomes clear that the yl peak belongs to unreacted epoxy groups the P peaks, undoubtedly, are related to some motions of aliphatic chains. The relaxation time as a function of temperature has been measured for two peaks — yt and p2 (dotted lines in Fig. 9c). Both peaks have been refined by... 

In this section, we shall consider only T of epoxy-aromatic amine networks as well as the influence of side reactions on T . The magnitude of Tgxp will be analyzed in Sect. 6. 

In Ref. 26 34) the mechanical behaviour of several epoxy-aromatic amine networks was analyzed in the rubbery state at temperatures of about T + 40 °C. Figure 14 gives some experimental results. If the rubber elasticity theory is obeyed, the following relation holds for uniaxial deformation ... 

Densely crosslinked epoxy-aromatic amine networks behave qualitatively as... 

It is well known that the elasticity of polymer networks with constrained chains in the rubbery state is proportional to the number of elastically active chains. The statistical (topological) model of epoxy-aromatic amine networks (see Sect. 2) allows to calculate the number of elastically active chains1 and finally the equilibrium modulus of elasticity Eca,c for a network of given topological structure 9 10). The following Equation 9) was used for the calculations of E, c ... 

The relationship between E ,c and E"p is given in Fig. 4. A very good correlation shows that all chemical heterogeneities of the epoxy-aromatic amine networks under consideration exist in the rubbery state only on the level of statistical deviations (see also Ref. 10,26)). 

Post-cure thermal treatment of epoxy-aromatic amine polymers stabilizes mechanical properties to a certain extent. However, the embrittlement makes the treatment harmful from the point of view of engineering material properties. 

Here, we shall consider several macroscopic features of the plastic deformation of glassy epoxy-aromatic amine networks. Mostly, the tensile or compression deformation has an inhomogeneous character. Usually, diffuse shear zones (or coarse shear bands) are clearly seen at room temperature deformation. Shear zones start from the defects on the sample boundaries or voids (dust) in the bulk. At higher temperatures, the samples are homogeneously deformed with neck formation (DGER-DADPhS, P = 1) 34>. 

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