Polysilane molecular weight distribution

Molecular weights of polysilane polymers depend upon the exact method of synthesis, as well as the purity of the dichlorosilane starting materials. Bimodal molecular weight distributions are commonly reported, as shown in Figure 1, but under some conditions... 

The molecular weight distributions were determined only in terms of the polystyrene equivalent from the polystyrene calibration of the GPC columns. This can only be regarded as semiquantitative, as the method determines only the relative hydrodynamic volumes. If the polysilane chain was significantly stiffer than polystyrene, the molecular weights would be estimated too high. If the chains are... 

The most common route to polysilane-high polymers is by the Wurtz-type alkali metal-mediated polycondensation of dichlorosilanes. However, , u-dihalooligosi lanes can also be coupled in a similar manner. Wurtz-type polymerization of BrSiMe2SiR2SiMe2Br led to bimodal molecular weight distributions of alternating co-polymers of the type (SiMe2SiR2SiMe2) (R = hexyl or Bu),17 as in Equation (1). 

Figure 3. Correlation between chemical core radius (rCQ) estimated experimentally by use of Eq. (1) and those (r ) theoretically predicted using Eq. (6). Molecular weight of the polysilanes are Mn = 2.6-4.6 x JO5 (PMPS1), 1.1-1.5 x 10s (PMPS2), 0.95-1.0 x l(f (PMPS3), and4.6-5.2 x 103 (PMPS4), respectively with small molecular weight distributions (Mw/Mn) less than 1.8.

Molecular weight distributions of polysilanes, determined by gel permeation chromatography (GPC), are frequently bimodal as shown in the example in Figure 7. The numerical values are calibrated using polystyrene standards, so the molecular weights... 

Another anionic ring-opening polymerisation that can also be used for the synthesis of a poly(germasilane) as well as a polysilane has been described by Sakurai and co-workers and is shown in Scheme 11.4. They are formed in greater than 40% yield and as well as having narrow molecular weight distributions (Mn = 17,000, Mw/M = 1.3) the polymers are highly ordered, as evidenced by NMR spectroscopy. 

The lack of sufficient control of molecular weight distributions, molecular weight and polymer structure of polysilanes via a Wurtz-type coupling reaction led Sakurai and co-workers to develop an alternative method for polysilane synthesis in 1989 [31],... 

The polymerization of these monomers in THF solutions with a catalytic amount of butyllithium gave the corresponding amino-substituted polysilanes 15a-d in high yields. Although polysilanes 15a and 15b were insoluble, 15c was soluble in various organic solvents. Since the solid state Si NMR spectra of 15a and 15b were almost similar to that of 15c, the insoluble polymer 15a and 15b are also pure amino-substituted polysilanes. The molecular weight distribution of 15c was determined by gel permeation chromatography calibrated by polystyrene standards with toluene as eluent Mn = 2.7 x 10", Mw n = 1.7. 

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