Crosslinking reactions complexes

Scheme 11. Basic crosslinking reaction by hydrosilylation catalyzed by a platinum complex.

Figure 1.23 Protein crosslinking reactions done using homobifunctional reagents can result in large polymeric complexes of multiple sizes and indefinite structure.

In contrast to the fairly simple crosslinking chemistry in urethane coatings, crosslinking in melamine-formaldehyde coatings can be quite complex. The following crosslinking reactions can be written for melamine coatings (29) ... 

The PMR-15 chemistry looks very straightforward and ideal for the application as a composite matrix resin. In addition, the starting monomers are readily available and cheap. The fact that the imidization reaction, which forms the prepolymer at moderately low temperatures, could be separated from the crosslinking reaction was thought to be the key to easy laminate processing and void free laminates. However, after more than twenty years of research and development, it is known that both reactions are very complex and dependent... 

Many fruit and vegetable juices darken in color with time due to enzymic browning. The phenolic compounds involved in the reaction complex with cyclodextrin. Thus, the browning reaction can be prevented, either by passing the juice through a crosslinked cyclodextrin polymer to remove the phenol, or by adding cyclodextrin to the juice, since polyphenoloxidase, the enzyme responsible for oxidizing the phenolic compounds, is unable to act on the phenolic compounds while they are complexed with the cyclodextrin.98,99... 

The microstructure of epoxy thermosets can be complex, and both molecular and physical microstructures are presumed. Unfortunately, the intractable nature of these materials makes direct structural characterization extremely difficult. The most accessible technique for direct structural characterization is evaluation of epoxy rubber-like properties above Tg. Sometimes, indirect characterization of epoxy structure is possible due to the fact that the chemistry of several epoxy systems is well behaved (e.g., epoxy-amine chemistry). This permits epoxy network structure to be modeled accurately as a function of the extent of the crosslinking reaction(s). This approach has been developed extensively by Du ek and coworkers for amine-linked epoxies ... 

There are two further possibilities for preventing segregation in complex immiscible mixtures. The first one Implies crosslinking reaction of the dispersed phase, associated with interfacial bonding and leads to the well-known dynamic vulcanisation (17). The second one results from mechanical interlocking of the phases which are created in interpenetrated polymer networks (IPN). 

In conclusion this work demonstrates the usefulness of NMR analysis methodologies for observing complex kinetic interactions of components associated with crosslinking reactions of polyethylene materials. 

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