Poly phenylmethylsilylene

GPC traces of poly(phenylmethylsilylenes) prepared in the ultrasonication bath are shown in Fig. 1. In contrast to thermal condensation, monomodal high molecular weight polymer is formed. Oligomeric cycles (mostly cyclic pentamer), formed usually in high yield (cf. Table 1), can be very easily separated from the reaction mixture by precipitation with isopropanol. The molecular weight of polysilanes decreases and polydispersity increases with temperature. 

Fig. 3. -NMR spectra of poly(phenylmethylsilylene) ([(SiPhMe)n]o=0.42 mol/L) (a), after reaction with triflic acid ([CF3S03H]o= 0.34 mol/L (b), and poly(methylmethoxysilylene) ([(SiOMeMe)n]o= 0.42 mol/L) (c) in CDCI3 using CH2CI2 as internal standard.

A recent flash photolytic study confirmed this unusual wavelength dependence for poly(phenylmethylsilylene). For this polymer also, irradiation at longer wavelengths... 

As an alternative to condensation of dichlorosilanes by alkali metals, it is possible to synthesize poly silanes by the reaction of preformed dilithio compounds with dichlorosilanes. An early synthesis of a copolymer by this route is illustrated in equation (19).10 (see also Section 5.9.2). Finally, poly(phenylmethylsilylene) has been made by thermal decomposition of a silyl-mercury polymer36 (equation (20)). 

Recently, ultrasound has been very successfully applied to different organ-ometallic and catalytic reactions (15). Rates are strongly accelerated, and reactions are often much more selective than those carried out under typical thermal conditions. Sonication of sterically hindered dichlorosilanes in the presence of lithium yields disilenes and cyclotrisilanes 16, 17). We have applied ultrasound in the synthesis of poly(phenylmethylsilylene) in the presence of dispersed sodium, which was prepared directly from small pieces of sodium by sonication. 

The rapid and quantitative displacement of phenyl groups from model silanes suggests that similar reactions with aryl-substituted polysilanes should lead to the triflated polymer. We have carried out this displacement under different conditions. Approximately the first 80% of the phenyl groups were removed rapidly from poly(phenylmethylsilylene). No free acid was observed... 

Figure 1. NMR spectra of poly(phenylmethylsilylene) modified by trifluo-romethanesulfonic acid (HA), (a) [Si(CeHs)(CH3)-]o = 0.42 molIL (b) after reaction with [HA]o = 0.17 molIL and (c) after reaction with [HA]o = 0.34 mollL. CH2CI2 was used as internal standard (5.35 ppm). Spectra were taken in CDCI3 solvent at 25 °C.

At present, no evidence exists for long runs of either meso or racemic placements in the Wurtz dechlorination reaction used in the synthesis of polysilylenes. Deviation from a random stereochemical polymerization has been suggested by West et al. (3) in the case of poly(phenylmethylsilylene) (PPMS). An analysis of Si NMR triads indicates that addition of monomer units with the same stereochemistry is preferred, which results in an increase in the intensity of syndiotactic and isotactic triad structures compared with a random stereochemical polymerization. 

Poly(phenylmethylsilylene) [-SiPhMe-] and Poly(silastyrene) [-SiPhH-SiH2-]... 

MM calculations with full geometry optimization have been carried out to calculate the molecular structure and conformational energies od, ..modeJ -.cpmpounds for poly (phenylmethylsilylene) [-SiPhMe-] and poly(silastyrene) [-SiPhH-SiH2-]. In each case the calculations considered both the isotactic and syndiotactic stereochemical isomeric forms of the model compounds. The structures considered are illustrated in Figures 6 and 7. 

Figure 4.2. The 750MHz H NMR of SiCH3 signal of isotactic poly[(phenylmethylsilylene) trimethylene].

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