Preform epoxy

A waterborne system for container coatings was developed based on a graft copolymerization of an advanced epoxy resin and an acryHc (52). The acryhc-vinyl monomers are grafted onto preformed epoxy resins in the presence of a free-radical initiator grafting occurs mainly at the methylene group of the aHphatic backbone on the epoxy resin. The polymeric product is a mixture of methacrylic acid—styrene copolymer, soHd epoxy resin, and graft copolymer of the unsaturated monomers onto the epoxy resin backbone. It is dispersible in water upon neutralization with an amine before cure with an amino—formaldehyde resin. 

Another potential route for the synthesis of organofunctionally terminated disiloxanes is the modification or transformation of preformed carbofunctional disiloxanes into others. For this purpose, disiloxanes with halogen, cyano and epoxy end... 

Fiber-Matrix Composites. As shown in Figure 1.75, there are two main classifications of FMCs those with continuous fiber reinforcement and those with discontinuous fiber reinforcement. Continuous-flber-reinforced composites are made from fiber rovings (bundles of twisted filaments) that have been woven into two-dimensional sheets resembling a cloth fabric. These sheets can be cut and formed to a desired shape, or preform, that is then incorporated into a composite matrix, typically a thermosetting resin such as epoxy. Metallic, ceramic, and polymeric fibers of specific compositions can all be produced in continuous fashions, and the properties of the... 

Figure 12.4 Compaction behavior of a woven carbon fiber fabric. The solid curve shows the behavior at room temperature the other two lines show the behavior at 100 C and 110°C. The fabric was factory treated with an epoxy preform binder...

Other chemistries have been used to prepare preformed reactive modifiers for epoxy and unsaturated polyester resins. Particles are generally composed of... 

Similarly prepared solid epoxy films can be ground into powder. The powder can be pressed into preformed pellets and applied directly to the adhesive joint as annular rings or... 

The powder can be applied directly to the substrate surface by electrostatic coating processes or dusting onto a warmed surface. It can also be formed into shapes or preforms by the application of pressure in a die mold. This process is similar to how pharmaceutical tablets are made. In this way shaped preforms can be made that will conform to a specific joint geometry. There are a wide variety of applications to which epoxy preforms can be adapted. They can be used to... 

There are several common forms of solid epoxy adhesives. These include film, tape, powder, and preformed shapes. Certain formulations are better suited for specific forms. For example, casting of tape or film adhesive from solvent solutions lends itself to working with multicomponent hybrid systems, where each resin can be solubilized and blended together in a universal solvent. B-staged systems are generally more brittle and better suited for powders or preformed adhesives. 

Solid epoxy adhesives may also be fused or compacted into various shapes or preforms (see Fig. 13.2) such as sticks, rings, and beads.5 They can then be easily applied to a specifically shaped part. Similar to thermoplastic hot-melt adhesives, these thermosetting epoxy adhesives flow on the substrate by heating. However, the product will cure to an infusible thermoset stage with continued heating. Once cured, the product demonstrates properties similar to those of other structural epoxy adhesives. These solid epoxy adhesives are sometimes referred to as thermosetting hot melts. 

FIGURE 13.2 Solid epoxy preforms are designed to provide a simple method for sealing or bonding high-volume components. Courtesy Multi-Seals, Inc., Manchester, CT.)... 

Preformed sticks or tubes of solid epoxy may also be applied much as a solder is.6 To apply, the area to be bonded is heated until sufficiently hot to cause the stick solder to flow when drawn across the surface. After application, the adhesive is cured by conventional thermal techniques. If two substrates are to be bonded, both must be preheated prior to... 

The resin matrix can be either thermosetting or thermoplastic. Thermosetting resins such as epoxy, polyimide, polyester, and phenolic are used in applications where physical properties are important. Polyester and epoxy composites make up the bulk of the thermoset composite market. Of these two, polyesters dominate by far. Reinforced with glass fiber, these are known as fiberglass-reinforced plastics (FRPs). FRPs are molded by layup and spray-up methods or by compression molding either a preform or sheet molding compound (SMC). 

Solid epoxy adhesives, such as powder, preforms, or film, are the least toxic because they have very low vapor pressures. However, they still can present a hazard when they are heated to a liquid and more volatile state to cure. 

Optically active allylic alcohols and homoallylic epoxides. The reaction of optically active 2,3-epoxy halides (1), available by Sharpless asymmetric epoxidation of allylic alcohols, with a preformed mixture of vinylmagncsium bromide and Cul (2 equiv. each) in THF at —23° does not result as expected (7.H1-82) in a homoallylic epoxide, but... 

Reaction of Sulfonyl-Stabilized Oxiranyllitbiums. Reaction of sulfonyl-stabilized oxiranyllitbiums with primary alkyl halides gives acceptable yields of products. More reactive alkyl triflates give generally better yields but, due to the instability of oxiranyl-lithiums, yields are often not reproducible when electrophiles are added to a solution of the preformed oxiranyllitbiums. It is recommended that the alkylation reaction be carried out by an in situ trapping method. Treatment of a solution of epoxy sulfone (1.0 equiv) and triflate (1.5 equiv) in THE-DMPU (or HMPA) at — 100 °C under argon with n-BuLi (1.0 equiv) followed by stirring... 

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