Crosslinking routes

Rubbers and PTFE powder were first premixed in an internal mixer for 5 min at a temperature of 100°C and at a rotor speed of 50 rpm. Figure 10 shows two different crosslinking routes, i.e., thermally or using electron irradiation. In the case of EPDM, crosslinking was performed thermally and also with electron irradiation. 

The product of the above reaction can be thermoset like any urea-formaldehyde resin (see Chapters 6 and 8). Many crosslinking routes are described in the patent literature, because there are many different functional groups available. 

Fig. 3 Two possible crosslinking routes a cationic growth via P molecular condensation with formation of P - O - P crosslinks...

The route to crosslinked phenol-formaldehyde resins via resoles corresponds to that used by Baekeland in his original commercial technique. They now tend to be used for adhesives, binders, and laminates. The resole... 

Fig. 4 Structures and formation routes of crosslinks in elastin. In the first step, lysine is catalyti-cally converted to allysine by lysyl oxidase all subsequent condensation steps are spontaneous...

In conclusion, the lesson learned from the research carried out to date on the subject of polycarbosilanes is that the general rule that linear, noncrosslinked polymers are not suitable preceramic polymers applies here as well. Crosslinked network-type polymers are needed. Such structures can be generated in more than one way, but in the case of the polycarbosilanes they have, to date, been obtained mainly by thermolytic routes thermal treatment (with or without other chemical additives) in the case of the Yajima polycarbosilanes and the thermolysis of tetramethylsilane in the case of the Bayer process-derived polycarbosilane. 

Crosslinked macromolecules can be formed from bifunctional monomers by first polymerising them, then by performing coupling reactions onto existing chains. The latter mechanism is often called vulcanisation.11 Several chemical routes can be followed to accomplish vulcanisation, depending on the functions available on polymer chains. 

Psoralens can react by two different routes upon photoactivation (Parsons, 1980 Pathak, 1984). The first route is through the well-known photoreaction mechanism that principally involves intercalation within double-stranded DNA or RNA with the formation of adducts with adjacent thymine bases. The furan-side and pyrone-side rings in psoralen both can form cycloaddition products with the 5,6-double bond of thymine to create a crosslink between two DNA strands (Reaction 57) or to a lesser extent, within double-strand regions of RNA. 

Figure 4.26 Glutaraldehyde may react by several routes to form covalent crosslinks with amine-containing molecules.

Another possible route to coupling ligands to amine particles is to use a bifunctional crosslinking agent to react with the amines and provide another reactive group at the other end to couple with the ligand. In this approach, virtually any reactive group desired can be formed on the... 

Activation of PE residues with these crosslinkers can proceed by one of two routes the purified PE phospholipid may be modified in organic solvent prior to incorporation into a liposome, or an intact liposome containing PE may be activated while suspended in aqueous solution. Most often, the PE derivative is prepared before the liposome is constructed. In this way, a stable, stock preparation of modified PE may be made and used in a number of different liposomal recipes to determine the best formulation for the intended application. However, it may be desirable to modify PE after formation of the liposomal structures to ensure that only the outer half of the lipid bilayer is altered. This may be particularly important if substances to be entrapped within the liposome are sensitive or react with the PE derivatives. 

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