Silyl radicals from polysilanes

Polysilanes as Photoinitiators. Since polysilanes photolyze to give silyl radicals,(21) as explained in the section on photochemistry above, they can be used as photoinitiators for radical processes such as polymerization.38 As can be seen from the information in Table II, this process is a fairly general one a variety of... 

It was proposed that an initially generated silyl radical 3, by reaction of i-BuO radical and polysilane 2, attacks another silicon atom in the same backbone to give a cyclic polysilane that contains an acyclic chain and another silyl radical (Scheme 8.1) [12]. The last silyl radical can either cyclize or abstract a hydrogen atom from another macromolecule, thus propagating the chain degradation. The reaction in Scheme 8.1 is an example of intramolecular homolytic substitution (ShO, a class of reactions discussed in Chapter 6. 

As a result of several decades of research it is now known that a polysilane of three or more contiguous silicon atoms is susceptible to reaction by one or more of several pathways when photolyzed, each associated with cleavage of a silicon-silicon bond. The two most common processes observed are the homolysis of a silicon-silicon bond to yield a pair of silyl radicals, and the elimination of a silicon atom from the chain in the form of a silylene. As discussed in Section VII, the use of trisilanes, particularly where the central silicon atom bears aryl groups, has become an important route for the preparation of a wide variety of diarylsilylenes, A Si , many of which have been captured in glasses at low temperature, or have been allowed to dimerize to disilenes by warming. 

Our group previously reported that radiation induced crosslinking reactions in polysilane derivatives are mainly promoted by side-chain dissociated silyl radicals, and that the predominant reaction is determined by the radical concentration in the ion tracks [14,20,21]. Thus, the distribution of crosslinks in an ion track is expected to obey the equations (2) and (3) given in the previous section, and the crosslinking reaction also gives cylindrical poly(methylphenylsilane) (PMPS)-based nanowires with fairly controlled sizes as shown in Fig. 2. Using the reported value of G(x) = 0.12 derived from... 

Much of the material summarized in this chapter will also be found, hopefully from a different perspective, in other chapters of this book, in particular the chapters on Silyl Radicals and Silylenes, Multiple Bonds to Silicon and Polysilanes. Readers are encouraged to consult these chapters for additional material and discussion. 

Polysilanes are highly susceptible to two forms of photochemical reaction, namely cleavage to silyl radicals which in the absence of trapping agents abstract hydrogen from... 

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