Poly phenylsilane

The functionalization of poly(phenylsilane) [99936-07-9] by reaction with CQ4 and with CBr4 has also been reported (117). This yields polymers containing Si—Cl or Si—Br bonds, but leaves the Si—C6H6 bonds intact. 

Free radical hydrosilylation of poly(phenylsilanes) (294) with alkenes, aldehydes or ketones promoted by 2,2 -azo(bisisobutyronitrile) (AIBN) provides functional polysilanes (295) possessing a variety of properties (equation 111)292. 

FIGURE 1. Synthesis of substituted poly(phenylsilane)s. (Reprinted from Ref. 11.)... 

Free radical chlorination of poly(phenylsilane) to produce poly (chlorophenylsilane) and then substitution with MeOFI or MeMgBr... 

Fluorescence of poly(phenylsilane) at room temperature was not detected. Poly(chlorophenylsilane) has a long wavelength tail out to 380 nm with a transition centered at 330 nm. Substitution of the Si-Cl bonds of the... 

The functionalization of polymers is another useful feature of the hydrosilation reaction. The introduction of highly fluorinated alkyl chains by the hydrosilation of Si-H groups of the polymer with fluorinated aUcenes is a typical example. Poly(phenylsilanes) obtained by the dehydrocouphng polymerization of phenylsilane undergo AIBN initiated free radical hydrosilation with aUcenes, ketones and aldehydes. Cross-linking and branching of polymers can also be easily accomplished using hydrosilation. 

The slight solubility of the poly(methylsilane) was sufficient enough to effect GPC investigations. The molecular weight distribution vs. polystyrene standard showed a relatively uniform chain length of fifteen Si units. Poly(phenylsilane) was completely insoluble, which made GPC analysis impossible, but calculations on base of elemental analysis yielded a chain length of more than 20... 

Poly(phenylsilane)s have been used as radical-based reducing agents for organic halides [70]. The reduction of a bromide is given as an example in Eq. (32). 1,1,2,2-Tetraphenyldisilane has also been introduced as a diversified radical reagent for the reduction of alkyl bromides and phenyl chalcogenides [71]. An example with 3-cholestanyl phenyl selenide is given in Eq. (33). 

Weak P-donor interactions could be the reason for the frequently reported high reactivity of hydroxylaminosilanes. These include claims for new cross-linking agents and cold-curing catalysts for silicone polymers [6], and more recently, the catalysis of the alkoholysis of Si-H functions in poly-phenylsilane [7]. 

Fig. 7.16. Synthesis of short-chain poly(phenylsilane)s by the catalytic dehydrogenation ofPhSiHa...

Free-radical-assisted hydrosilylation can be carried out on poly(phenylsilane), H(PhHSi)nH. Various types of reactive substrates such as 1-hexene, cyclohexanone etc., have been utilized and about 70-90% of substitution was observed without much chain degradation (Fig. 7.19). 

Similarly, the conversion of the Si-H unit in poly(phenylsilane) into the more reactive Si-Cl and Si-Br functional group can be easily effected by the reaction with carbon tetrachloride and carbon tetrabromide, respectively (Fig. 7.19) [63]. The chlorination or bromination does not affect the Si-Ph substituent but only involves the Si-H bonds. In these reactions about 80% of the Si-H bonds can be converted into the corresponding Si-X bonds. These halogenated polysilanes are reactive polymers that can react with other types of nucleophiles such as alcohols to afford polysilanes containing alkoxy groups [63]. 

Free radical chlorination of poly(phenylsilane) produces poly(chlorophenylsilane) These chlorinated polymers can be substituted with a variety of nucleophiles such as MeOH or MeMgBr with high selectivities. The spectroscopic properties of these materials are extremely sensitive to the nature of the substituent attached to the polymer backbone. The UV properties of a series of polysilanes containing Si-H, Si-Cl, Si-R and Si-OR functionalities are reported. The absorption maximum of poly(phenylsilane) appears at 294 ran (esi-si = 2489 cm-iM 0 whereas that of poly(methylphenylsilane) appears at 328 nm (esi-si = 4539 cm-iM-i). The absorption spectra of poly(metiioxyphenylsilane) are red shifted considerably relative to the other polymers (X = 348 nm, esi-si = 2710 cm- M-O. These substituent effects are likely due both to conformational as well as electronic perturbations on tfie Si-Si backbone chromophore. 

The effect of substitution reactions on the number average molecular weight (M ) of the polymer was investigated by vapor pressure osmometry. Chlorination of poly(phenylsilane) results in a decrease in the degree of polymerization (DP) from about 40 to 25 silicon atoms (Table I). Subsequent substitution of Si-Cl with Si-OMe further degrades the polymer to less than 15 monomer units. Methylation of poly(chlorophenylsilane) with MeMgBr affords, upon purification, a 41% yield of poly(methylphenylsilane) of approximately the same de ee of polymerization as the original poly(phenylsilane). 

Spectroscopic Properties. The UV absorption spectrum of poly(phenylsilane) 1 contains a weak transition at 294 nm (esi-si = 2489 crn- M Figure la). The absorption band assigned as the Si(o-a ) transition occurs at 294 nm and likely contains considerable phenyl (tc-tc ) character, as suggested by energy band calculations.((55) In contrast to other substituted polysilanes of similar molecular weight, we were unable to detect fluorescence for poly(phenylsilane) at room temperature in THF. 

Although the introduction of halogen-containing substituents into linear polysilanes have been reported,(55, 41, 45) further modification of structure and electronic properties of Aese polysilanes have not been extensively studied. We have recently reported that free-radical chlorination of poly(phenylsilane) with CCI4 provides a facile synthesis of poly(chlorophenylsilane), a versatile synthon for the preparation of a variety of functionalized poly(phenylsilane).(59) TTiis new synthetic capability has allowed us to investigate the influence of polymer substituent on the electronic properties of poly silanes. 

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