Epoxy degradation

Characterization of the chemical structure of highly cross-linked polymers, and of the chemical changes that accompany degradation processes, relies on spectroscopic methods. Solid-state nuclear magnetic resonance techniques have the potential to allow a more detailed characterization than before possible of the chemical environment and structure of chemical crosslinks in elastomers and thermoset epoxies. Degradation processes in cross-linked systems have been studied by using infrared spectroscopy, solid-state NMR, and electron spin resonance. 

Gale, R. J., Epoxy degradation induced Au-Al intermetallic void formation in plastic encapsulated MOS memories. Reliability Physics Symposium Proceedings, 22 (1984) 37. 

Calorimetry is an effective analytical tool to characterize the physical properties of a polymer. It allows us to determine melting, crystallization, and mesomorphic transition temperatures and the corresponding enthalpy and entropy changes. The glass transition and other effects that show changes in either heat capacity or latent heat can also be smdied. Hie latter particularly includes chemical reactions such as curing of epoxies, degradation, and loss of volatile components. 

Sihcones (qv) have an advantage over organic resias ia their superior thermal stabiUty and low dielectric constants. Polyurethanes, when cured, are tough and possess outstanding abrasion and thermal shock resistance. They also have favorable electrical properties and good adhesion to most surfaces. However, polyurethanes are extremely sensitive to and can degrade after prolonged contact with moisture as a result, they are not as commonly used as epoxies and sihcones (see Urethane polymers). 

Other materials that are often referred to as secondary plasticizers iaclude materials such as epoxidized soybean oil (ESBO) and epoxidized linseed oil (ELO) and similar materials. These can act as lubricants but also as secondary stabilizers to PVC due to thein epoxy content which can remove HCl from the degrading polymer. 

Although the above experiments involved exposure to the environment of unbonded surfaees, the same proeess oeeurs for buried interfaces within an adhesive bond. This was first demonstrated by using electrochemical impedance spectroscopy (EIS) on an adhesive-covered FPL aluminum adherend immersed in hot water for several months [46]. EIS, which is commonly used to study paint degradation and substrate corrosion [47,48], showed absorption of moisture by the epoxy adhesive and subsequent hydration of the underlying aluminum oxide after 100 days (Fig. 10). After 175 days, aluminum hydroxide had erupted through the adhesive. 

Keto steroids can be obtained in excellent yields via the Beckmann degradation of 17a-hydroxy-or 16a,17a-epoxy-20-ketopregnanes. In the case of the 17-hydroxy compounds, substituents at C-16 readily survive e.g., 16 -Br, 16jS-Cl, Iba-OAc). The 16,17-oxido-20-oximinopregnanes produce 16a-acetoxy-17-ketones. 

Rearrangement of a,/B-epoxy ketones to ftdicarbonyl isomers, 307 Reductive alkylation, 97 Reductive cleavage of halo ethers, 264 Reductive degradation of 19-substitutional steroids, 277, 278 Reformatsky reaction, 139 Removal of the C-10 substituent in steroids. 272... 

The degradation of the matrix in a moist environment strongly dominates the material response properties under temperature, humidity, and stress fatigue tests. The intrinsic moisture sensitivity of the epoxy matrices arises directly from the resin chemical structure, such as the presence of hydrophilic polar and hydrogen grouping, as well as from microscopic defects of the network structure, such as heterogeneous crosslinking densities. 

Phenolic degradation, thermal and thermo-oxidative, 418-425 Phenolic-epoxy networks, 413 Phenolic monomers, second-order reaction rate constants of formaldehyde with, 403... 

The products of the chemical degradation of PETP with triethylene tetramine and triethaneolamine can be used as epoxy resin hardeners, it is demonstrated. Products of PETP aminolysis with triethylene tetramine and aminoglycolysis with triethanolamine, were characterised using NMR and rheometric measurements. Characteristics of the crosslinking process for the system epoxy resin/ PETP/amine degradation product, and epoxy resin/TETA for comparison were investigated by DSC. Three classes of liquid epoxy resins based on bisphenol A, bisphenol F and epoxy novolak resins were used in the experiments. 16 refs. 

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