Poly hydrosilane s

Two different kinetic approaches have been used to obtain mechanistic information [15,16]. Kinetic studies carried out by EPR spectroscopy using fusinite as a paramagnetic probe of the oxygen concentration allowed the oxidizability of poly(hydrosilane)s to be obtained [15]. Oxidizability values of 1.8 x 10 and 

2 X 10 (referring to each SiH moiety) were found for poly(phe- 

The values of oxidizability obtained for poly(hydrosilane)s are comparable with the 1.9 X 10 M s of methyl linoleate, an example of easily oxidiz- 

The reaction mechanism for the radical chain oxidation of poly(phenylhydrosi- 

The homologous (Me3Si)2Si(H)Me does not react spontaneously with air or molecular oxygen at room temperature. However, a reaction takes place at 80 °C when air or molecular oxygen is bubbled into the pure material or its solutions to form a major product that contains the siloxane chain (Reaction 8.5) [15]. In general, yields of siloxane are about 50%. Also in this case the reaction is accelerated by radical initiation and retarded by common radical inhibitors. 

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Poly(hydrosilane)s are stable compounds and can be manipulated in the air only for a short period since they are oxygen-sensitive. The oxidized products obtained from poly(phenylhydrosilane) exposed to the air contain the units 119-122 without the formation of silyl hydroperoxides and peroxides. In particular, units 119,120, and 121+122 were present in the relative percentages of 27,54, and 19%, respectively, which means that more than 70% of the catenated silicons are altered. 

Poly(hydrosilane)s have been used as radical-based reducing agents for organic halides (RX, where X = Cl, Br, 1), rivaling the effectiveness of the (TMSlsSiH. A rate constant (fcn referring to each SiH moiety) in the range of (5-60) xlO M s is estimated for the reaction of primary alkyl radicals with 123. ... 

Silyl radicals generated from both phenyl and n-hexyl substituted poly-(hydrosilane)s add readily to a variety of compounds containing C = C and 0 = C moieties to give the corresponding radical adducts for which EPR spectra have been recorded. ... 

Poly(hydrosilane)s have been successfully applied as processing stabilizers for organic polymeric materials subject to oxidative degradation. The degradation of polyolefins during processing takes place by a widely accepted... 

Among the various synthetic procedures for polysilanes is the Harrod-type dehydrogenative coupling of RSiH3 in the presence of Group 4 metallocenes (Reaction 8.1) [5,6]. One of the characteristics of the product obtained by this procedure is the presence of Si—H moieties, hence the name poly(hydrosilane)s. Since the bond dissociation enthalpy of Si—H is relatively weak when silyl groups are attached at the silicon atom (see Chapter 2), poly(hydrosilane)s are expected to exhibit rich radical-based chemistry. In the following sections, we have collected and discussed the available data in this area. 

Poly(hydrosilane)s are stable compounds and can be manipulated in the air only for a short period since they are oxygen sensitive. In order to study the oxidation products, a xylene solution of poly(phenylhydrosilane)(Mw = 2340, Mw/Mn = 1.72) was refluxed (140 °C) for 12 h in a system exposed to the air [15]. Only minor changes were observed by GPC analysis whereas FTIR showed characteristic absorptions due to siloxane-type structures on the polymer backbone. A detailed NMR analysis, based on H NMR, Si INEPT and H- Si HMQC spectroscopies, indicated that the oxidized material contains the units 7-10 shown in Scheme 8.2. In particular, units 7,8 and 9+10 were present in relative percentages of 27%, 54% and 19%, respectively, which mean that more than 70% of the catenated silicons were altered. It has also been reported that silyl hydroperoxides and peroxides are not found as products in the autoxidation of poly(phenylhy-drosilane) [16]. 

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