Epoxy resin oligomers structure

In the narrow sense, bis-maleimide resin means the thermosetting resin eom-posed of the bis-maleimide of methylene dianiline (BMI, bis(4-maleimidophenyl)-methane) and methylene dianiline (MDA, bis(4-aminophenyl)methane) (Fig. 1). Beeause of the addition meehanism, the resin is eured without elimination, whieh is a eharacteristic of this resin. Bis-maleimide resin is used as a thermally stable matrix up to 204°C (400 F) whieh typical epoxy resins may not normally be used. However, in spite of having an imide structure, bis-maleimides are classified as being moderately thermally stable resins. The aliphatic structure of the resin is not stable for long periods above 232°C (450°F.) If a highly aromatic thermally stable thermosetting resin is necessary, acetylene end-capped aromatic imide-based oligomers should be used. 

The epoxy resin most frequently used is the oligomer of the diglycidyl ether of bisphenol-A (DGEBA) whose chemical structure is shown below [1-3]. 

Epoxy resin polymer modified perfluoroether oligomer, hydroxyl terminated - interpenetrating networks (max. 14.3 wt.-% oligomer) - particle-matrix structure (max. 10 wt.-% oligomer) 13.0 - 30.0 19.0-31.0 03Rag... 

Studies of the dependence of EEC properties obtained as above on the formation method showed that the precipitated finely dispersed rubber that is not bonded to the epoxy matrix does not endow it with high mechanical characteristics. When reactive oligomers are applied with high-temperature cure, there is a sharp enhancement of the modifying efficiency, accounting for the more intensive separation of the phases in the system and for the increase of the yield of the epoxy rubber copolymer. Thus, the structure and properties of epoxy resins modified by rubbers are mainly determined by the mode of system curing, but the quantitative relationships between curing mode and final properties have not been sufficiently studied. 

In studies of the ERC heterogeneous structure obtained in copolymerization between the epoxy and rubber oligomers that occurs along with the epoxy resin cure (i.e., hot cure compoimds), the average size of the rubber particles was found to be dependent on its polarity and on the level of compatibility with the epoxy resin as well as on the chemical composition of the modifier [132]. The author also showed that the size of the rubber inclusions decreases and the structure of the composition becomes more homogeneous with increase of the polarity of the elastomers and the curing temperature of the ERC. 

The adhesion properties of ERC are directly related to their phase structure. When comparing the values of X2,3 that characterize the thermodynamic stability of the oligomer mixtures (epoxy resins— rubbers and curing agents-rubbers) with the values of Tad, similar dependence is observed for ERC obtained by the method with PER. The maximum value of the ERC adhesion strength corresponds to that quantity of the rubber at which X2,3 is maximal. 

Fig. 2. Chemical structures of common epoxy resins a) 2,2-Bis[4-(glyddyloxy)phenyl] propane (DGEBA) b) 3,4-Epoxycyclohexylmethyl-3,4-epoxycydohexanecarboxylate (ECC) c) DGEBA oligomer, n = 0.2 typically.

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