Cross-linked epoxy amine polymers structure

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. 

Properties of the thermosetting polymers are controlled by the molecular composition and structure such as the stoichiometric ratio between the reagents, and the cross-link density of the network. Accordingly, fatigue crack propagation of an Epon 828 MDA epoxy has been examined [96] with respect to amine epoxy ratio and cross-link density. 

The effect of hardener structure on heat resistance of a cross-linked DGEBA resin is shown in Table 19 (140). Thermal stability is affected by the structin-e of the hardener. The heat resistance of aliphatic amine cimed epoxy is low as measured by TGA. The nitrogen atoms are oxidized by atmospheric oxygen to amine oxides, which attack the polymer backbone. Anhydride systems tend to spht off the anhydride at temperatures well below their decomposition point at about 390°C. The ether segments formed by 2-MI and phenohc cured epoxies have the highest thermal stability. 

Evidence for this scheme is that chemically-bound nitrogen is found in the final product the rate of reaction is increased by the presence of phenols and anhydrous non-phenolic tertiary amines are not effective curing agents. Since bisphenol A-epichlorhydrin resins have epoxy groups at each end of the polymer the above scheme results in the formation of a cross-linked polymeric structure. 

As results obtained in Refs. [34, 39] have shown, the behavior of cross-linked pol5nners is just slightly different from the above-described one for linear PC and PAr. However, further progress in this field is quite difficult due to, at least, two reasons excessive overestimation of the chemical crosslinks role and the quantitative structural model absence. In the Ref [39] the yielding mechanism of cross-linked polymer has been offered, based on the application of the cluster model and the latest developments in the deformable solid body S5meigetics field [40] on the example of two already above-mentioned epoxy polymers of amine (EP-1) and anhydrazide (EP-2) curing type. 

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