Dichlorosilanes copolymerization

The principal dichlorides used in this study were hexylmethyl-dichlorosilane (HMDS) and phenylmethyldichlorosilane (PMDS), some copolymerizations of the latter and dimethyldichlorosilane (DMDS) were also made. The usual practice was to add the dichloride (20 vol.%) in one portion to the refluxing reaction mixture at the start of the reaction. This usually entailed cooling the reaction mixture when PMDS was used to prevent a too vigorous reflux at the beginning of the reaction. In all cases the reaction turned dark purple and ultimately viscous. 

Sonochemical homopolymerization of dichlorosilanes in the presence of sodium is successful at ambient temperatures in nonpolar aromatic solvents (toluene or xylenes) only for monomers with a-aryl substituents. Dialky 1-dichlorosilanes do not react with dispersed sodium under these conditions, but they can be copolymerized with phenylmethyldichlorosilane. Copolymers with a 30-45% content of dialkylsilanes were formed from equimolar mixtures of the corresponding comonomers. Copolymerization might indicate anionic intermediates. A chloroterminated chain end in the polymerization of phenylmethyldichlorosilane can participate in a two-electron-transfer process with sodium (or rather two subsequent steps separated by a low-energy barrier). The resulting silyl anion can react with both dichlorosilanes. The presence of a phenyl group in either a or P position in chloroterminated polysilane allows reductive coupling, in contrast to peralkyl species, which do not allow the reaction. Therefore, dialkyl monomers can copolymerize, but they cannot homopolymerize under sonochemical conditions. 

Copolymerization of two different dichlorosilanes can also be achieved by the reduction using a sacrificial anode [177,178]. It is interesting that copolymerization of sila-functional dichlorosilanes with simple dichlorosilanes took place smoothly to provide an elegant route to functionalized polysilanes [178]. As to the synthesis of sila-functional polysilanes, the electrochemical reduction of perfluoroalkyl-substituted trichlorosilane to give perfluoroalkyl-substituted polysilane is interesting [179]. 

Dendritic polysilanes have been prepared by stepwise reactions (56). Copolymerization of dichlorosilane and trichlorosilane yields ladder-type material (57). 

In contrast to growing interest with polysilanes, their preparation method is still limited. They have been traditionally prepared by the Wurtz-type condensation of dichlorosilanes with alkali metal (Kipping method). This method, however, requires drastic reaction conditions and, hence, is often limited in the type of substituents that are allowed to be located on the dichlorosilane monomer and also has a disadvantage in controlling the unit structure in the copolymerization. Several modified or alternative methods have been... 

Ishifune M, Sana C, Ando M, Tsuyama Y (2011) Electroreductive block copolymerization of dichlorosilanes in the presence of disilane additives. Polym Int 60(8) 1208-1214... 

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