Polysilane polymers synthesis

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... 

More recently Kashimura et al. [96] has investigated the effect of ultrasound on the electroreductive synthesis of polysilanes, polymer germanes and related polymers using magnesium electrodes. They found that the presence of ultrasound greatly facilitated the reactions. 

Burkhard, who reported the synthesis of polydimethylsilane, [Me2Si] , from sodium metal and dimethylchlorosilane in toluene (equation 31). This polymer is a highly crystalline substance which decomposes without melting and is insoluble in all common solvents. Its intractable nature may have contributed to the relative neglect of polysilane polymers over the next three decades. 

Polymer synthesis. All reactions are carried out in glassware that is dried under a dry nitrogen gas atmosphere. Details of the homopolymer synthesis (poly-5, poly-6 and poly-7) have been described in previous papers. Addition of a catalytic amount of 18-crown-6 and 15-crown-5 to most reactions of dialkyldichlorosilanes with sodium in hot toluene leads to reproducible high yields of HMW polysilanes with a monomodal distribution. However, several alkyl-3,3,3-trifluoropropyldichlorosilanes are exceptions and do not produce the corresponding homopolymers when crown ethers are present in the reaction mixture (Chart 13.25). 

Polymerization ofiVIasked Disilenes. A novel approach, namely, the anionic polymerization of masked disilenes, has been used to synthesize a number of poly(dialkylsilanes) as well as the first dialkylamino substituted polysilanes (eq. 13) (111,112). The route is capable of providing monodisperse polymers with relatively high molecular weight M = lO" — 10 ), and holds promise of being a good method for the synthesis of alternating and block copolymers. 

With the success of CgK in the syntheses of 41 and related co-polymers, the same methodology was applied to the synthesis of polysilanes bearing pendant crown ether substituents, viz. 42-44,150,151 which were synthesized in yields from 6% to 28%, with molecular weights of the order of 104. The polymers were found to be water soluble and thermochromic in accordance with the Schweizer thermochromism theory (see Section 3.11.5.2.4).152... 

There have been very few reports of polysilanes containing a carbon functional group such as unsaturated groups directly attached to the silicon main chain. This appears to be due to the difficulties in synthesis and characterization due to instability of these compounds. These polymers are expected to show significant differences to conventional polysilanes in their properties due to the interaction of main-chain cr-electron and side-chain 7r-electron systems. 

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