Elastomer-modified epoxy morphology

W. A. Romanchick, J. E. Sohn, and J. F. Geibel Synthesis, Morphology, and Thermal Stability of Elastomer-Modified Epoxy Resin, in ACS Symposium Series 221 — Epoxy Resin Chemistry II, R. S. Bauer (ed.), American Chemical Society, Washington DC, 1982, pp. 85-118. 

Synthesis, Morphology, and Thermal Stability of Elastomer-Modified Epoxy Resins... 

Figure 2. Morphology of Cured Elastomer Modified Epoxies.

Consequent to documentation surrounding methods of employing reactive nitrile elastomers to modify epoxy resins is a growing body of literature which serves to characterize and elucidate these systems. Such topics as morphology in the cured and uncured state, transitions from toughening to flexlbilization, viscoelastic effects, equilibrium physical properties and phase structure are available to the investigator (12-17). 

All of the above solid rubber-modified epoxy resins visually displayed clearly biphasic morphological properties (i.e., discreet rubber domains in a continuous epoxy matrix). If there is a reaction between a rubber moiety and an epoxide, it would best be studied in a homogeneous reaction mixture. Lower molecular weight epoxy resins are more compatible with CTBN elastomers and will form homogeneous solutions at elevated temperatures. Reaction of an epoxide with a reactive moiety contained in the elastomer, R, will most likely obey the following rate law ... 

It is evident that closely related types of information are conveyed concerning the morphology of CTBN modified epoxy resins by the small deformation data in the upper curves of Figure 8 and the tensile fracture data in the lower curves. Both deformation and fracture data tend to identify a morphological phase change in CTBN modified epoxy above 17% CTBN content wherein the elastomer and epoxy phase become co-continuous. In fact, the curves of Figure 8 appear to imply the essential disappearance of a pure epoxy phase at 50% CTBN as evidenced by loss of the T = 80 C singularities in both E(t) versus T (upper curves) and W versus T (lower curves). 

Composition (type of polymeric components). The base polymer (which is to be modified) may be an amorphous polymer [e.g., polystyrene (PS), styrene-acrylonitrile copolymer, polycarbonate, or poly(vinyl chloride)], a semicrystalline polymer [e.g., polyamide (PA) or polypropylene (PP)], or a thermoset resin (e.g., epoxy resin). The modifier may be a rubber-like elastomer (e.g., polybutadiene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, or ethylene-propylene-diene copolymer), a core-shell modifier, or another polymer. Even smaller amounts of a compatibilizer, such as a copolymer, are sometimes added as a third component to control the morphology. 

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