Peroxide translation system

In the zeolite hosts, the high translational mobility of the radicals seems to be a consequence of several factors, including low loading levels of peroxide, the excess photolytic energy of 82 kcal/mol and the driving force generated by the incipient CO2 molecules. Further ESR studies on these and other peroxide/zeolite systems are in progress. 

In both the case of epoxidations via j2-peroxides and that of diolate cycloreversion, chemists must exercise caution that the mechanistic lessons learned for rhenium may not translate to processes mediated by other metals, ligands, or oxidation states. This has always been a particular problem in mechanistic organometallic chemistry. However, it is likely that systems can be developed based on the observations described here that can discern the structural features that control competing mechanistic manifolds. 

For the tetraatomic system HXXH, representing both the linear acetylene and the non-linear hydrogen peroxide, we expect to be able to construct twelve symmetry coordinates. Three of them are translational, whereas two of the remaining nine in the linear conformation and three in the non-linear one are reserved for rotations. Linear tetraatomics thus have seven vibrational coordinates, motion along which changes the potential energy, whereas their nonlinear counterparts have six. Those of the linear HXXH molecule are shown in Fig. 4.4 with the subgroup into which each is taken, if only momentarily, by the displacement. 

Another method of compatibihzation involves crossUnkingbetween the phases of a phase separated system. This method is employed in one of the most common of commercial polymer blends, i.e., elastomer blends utilized in tire construction. In order to achieve the proper balance of properties for tire applications, crosshnked blends of phase separated elastomers are often employed. Sulfur (or peroxide) crosslinking will lead to covalent bridges between the phases, thus assuring proper translation of mechanical stress from one phase to the other. 

Peroxide initiators are equally effective, but often kinetically faster, than platinum-based crosslinking systems. The crosslinking of silicon-based polymers with organic peroxides is well-known, and in this section several examples will illustrate the translation of this technology to preceramic polymer systems. For many vinyl-substituted precursors, and polysilazanes in particular, free radical-based crosslinking is the cure chemistry of choice. 

---