Bonding, secondary operations

Overmolding is the process by which two different materials are joined into one assembly without using secondary operations like gluing or welding. In case the materials are chemically compatible, chemical bonds may form between them and so mechanical interlocks are not required. There are two common techniques of overmolding—insert molding and multiple-shot injection molding. 

Enamines. The condensation of a secondary amine and a ketone to make an enamine is a well known reaction which has seen wide use in organic synthesis [176-178]. Imines of a primary amine and a ketone exist in a tautomeric equilibrium between the imine and secondary enamine forms, although in the absence of additional stabilization factors cf. Scheme 5.33), the imine is usually the only detectable tautomer. Nevertheless, the enamine tautomer is very reactive toward electrophiles and Michael additions occur readily [179]. The mechanism of the Michael additions of tertiary and secondary enamines are shown in Scheme 5.34. For tertiary enamines, the Michael addition is accompanied by proton transfer from the a -position to either the a-carbon or a heteroatom in the acceptor, affording the regioisomeric enamine as the initial adduct [180]. The proton transfer and the carbon-carbon bond forming operations may not be strictly concerted, but they are nearly so, since conducting the addition in deuterated methanol led to no deuterium incorporation [180]. 

For joints which exhibit solely interfacial failure then obviously i = 1 and, from Equation 7.9, Go takes the same value as Go (interfacial). Hence, if only secondary bonds are operating across the interface then the value of Go should be equal to the value of the thermodynamic work of adhesion, Wa, as may be seen from the data in Table 3.5. Alternatively, if stronger interfacial forces are present, such as primary bonds, then the value of Go is much greater than VTa, as may be seen from the results in Fig. 4.3. 

Die compaction of a blended powdered material into a green compact which is then sintered with heat to increase the bond strength. Usually secondary operations are performed to improve dimensional accuracy, surface roughness, strength and/or porosity (see 3.11 F). 

The preparation of amines by the methods described m this section involves the prior synthesis and isolation of some reducible material that has a carbon-nitrogen bond an azide a nitrile a nitro substituted arene or an amide The following section describes a method that combines the two steps of carbon-nitrogen bond formation and reduction into a single operation Like the reduction of amides it offers the possibility of prepar mg primary secondary or tertiary amines by proper choice of starting materials... 

Some species have a large number of exchangeable hydrogens. Thus, metal ions with many coordinated water molecules will become completely deuterated in D20. For example, Co(H20) + becomes Co(D20) +. If there were a 2 percent secondary kie per bond, it would be amplified to (1.02)12 or 1.27. It would not be a simple matter to demonstrate the operation of a primary kie in such a system because of this, given the p/f difference between the two metal ions and the general effects of the solvent change. 

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