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The other production route for epoxy resins is the conversion of aliphatic or cycloaliphatic alkenes with peracids: [13] [14] In contrast to glycidyl-based epoxy resins, this production of such epoxy monomers does not require an acidic hydrogen atom but an aliphatic double bond. The epoxide group is also sometimes referred to as an oxirane group.
These molecules have bond angles between ring atoms which are more acute than the optimal tetrahedral (109.5°) and trigonal planar (120°) bond angles required by their respective sp 3 and sp 2 bonds. Because of the smaller bond angles, the bonds have higher energy and adopt more p-character to reduce the energy of the bonds. In addition, the ...
It is a precursor in the production of epoxy resins. [19] Halohydrins react with base to give epoxides. [20] The reaction is spontaneous because the energetic cost of introducing the ring strain (13 kcal/mol) is offset by the larger bond enthalpy of the newly introduced C-O bond (when compared to that of the cleaved C-halogen bond).
A bond of higher bond order also exerts greater repulsion since the pi bond electrons contribute. [10] For example in isobutylene, (H 3 C) 2 C=CH 2, the H 3 C−C=C angle (124°) is larger than the H 3 C−C−CH 3 angle (111.5°). However, in the carbonate ion, CO 2− 3, all three C−O bonds are equivalent with angles of 120° due to resonance.
A bond angle is the geometric angle between two adjacent bonds. Some common shapes of simple molecules include: Linear: In a linear model, atoms are connected in a straight line. The bond angles are set at 180°. For example, carbon dioxide and nitric oxide have a linear molecular shape.
Adhesives may be broadly divided in two classes: structural and pressure-sensitive. To form a permanent bond, structural adhesives harden via processes such as evaporation of solvent (for example, white glue), reaction with UV radiation (as in dental adhesives), chemical reaction (such as two part epoxy), or cooling (as in hot melt).
An epoxy may be used for mounting, but can lead to failure in the epoxy/polymer interface instead of in the bonded joint. [2] The most common method for testing solvent bonds is the tensile shear test using a lap joint configuration. Specimens are tested in shear to failure at a given overlap cross section via tensile loading.
This page was last edited on 16 January 2005, at 10:46 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply.
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