Polysilastyrene

This adventitious finding led to synthesis of the "polysilastyrene" family of Me2Si-PhMeSi copolymers.(11) At almost the same time, soluble polysilanes were reported by Trujillo(12) at Sandia Laboratories and by Wesson and Williams(12) at Union Carbide Co. 

Research in polysilane polymers grew slowly at first after this reawakening. But within the past few years, both the unusual scientific interest and the technological possibilities of the polysilanes have been recognized, and activity in this field has increased sharply. Commercial manufacture of both poly dimethylsilylene) and "polysilastyrene" is now being carried out in Japan, so that these two polymers are readily available in quantity. 

Soluble polysilane polymers can also be used as precursors to silicon carbide. The first such application, using (PhMeSi)n-(Me2Si)m copolymers ("Polysilastyrene"), was to strengthen silicon nitride ceramics. The Si3N4 ceramic body was soaked in polysilane and refired, leading to the formation of silicon carbide whiskers in the pore spaces and a consequent increase in strength. (U)... 

As these experiments indicate, polysilanes can in some cases be converted to silicon carbide directly, without the necessity for formation of polycarbosilane, fractionation, or oxidation. For example, polysilastyrene copolymers can be formed into films or fibers and then crosslinked by irradiation with UV light. The crosslinked polysilane forms silicon carbide when heated to 1100°C in vacuum. (1U This method can be used in a "printing" mode, if a film of polysilane is cast onto a ceramic or metal substrate, then... 

West and co-workers [9,10] prepared polysilastyrene, a soluble and fusible polymer, by a Wurtz-coupling of dimethyldichlorosilane and methylphenyldichlorosilane (Eq. 4). Thermolysis of this polymer at 450°C results in a polycarbosilastyrene which can be cured by irradiation with UV-light in air at room temperature [11],... 

Molecular mechanics techniques are employed to calculate the molecular structure and conformational energies of model compounds for polyphenylmethylsllylene and polysilastyrene. In both isotactic and syndiotactic stereochemical forms. The structural and conformational energy data provided are used to calculate, by application of the RIS theory, the unperturbed chain dimensions, given as the characteristic ratio, and its temperature coefficient. 

A nearly fully ordered polysilane copolymer has been synthesized by careful condensation of a 1,3-dibromotrisilane, yielding the AABAAB-type copolymer shown in equation (30).118 The best method for obtaining ordered polysilane copolymers is however by the anionic polymerization of masked disilenes (Section 5.3.3). Formation of an ABAB-type copolymer is illustrated in equation (31).119 These polymers show only two narrow lines in their 29Si NMR spectra, consistent with their ordered structure. In a similar reaction, the Sakurai group synthesized an exactly alternating polysilastyrene polymer, (PhMeSi-SiMe2) .120... 

Other linear polysilanes can also be used as ceramic precursors. Solid objects of silicon carbide are manufactured by Nippon Soda Co. from polysilastyrene and finely divided silicon carbide powder.133 These materials are blended, injection molded to the... 

The silicon-branched polymer also became semiconducting upon exposure to iodine vapor it is, therefore, closely related to polysilastyrene , for which West et al. (2) used highly toxic pentafluoroarsine as dopant. Polymer 1 is originally insulating, but an iodine-doped sample, a black solid, showed a conductivity (a) of I0" /fl-cm. The black solid was stable in air for several days and then gradually softened. The stability of the doped sample remains to be improved further. 

Thermogravimetric analysis of the polymer was carried out under very nearly the same conditions as previously reported for permethylpolysilane and polysilastyrene (17, 18) (Figure 5). Unfractionated polymer 2 lost 35% of its weight upon heating under nitrogen at a 10 °C/min rise in temperature, up to 800 C. The theoretical loss according to equation 4 or 5 is 27 or 40%, respectively, and the results indicate that practically no volatile silicon compounds have been driven off. 

West et al. (17) have reported that permethylpolysilane is completely lost at 650 °C, whereas 70% of a sample of polysilastyrene was lost as volatile... 

Partially pvrolvzed poivsilastyrene membranes. Molecular sieve membranes can also be made from porous solids other than carbon and zeolitic materials. One such potential candidate is the family of precursors of silicon carbide. Among the possible precursors, polysilastyrene (phenylmeihylsilane-dimethylsilane copolymer) is commercially available and soluble in many common solvents such as toluene and tetrahydrofuran and can be crosslinked by UV radiation. Polysilastyrene is comprised of long chains of silicon atoms ... 

Figure 4.15 Use of three molecules to determine the evolving pore size distributions of partially pyrolyzed polysilastyrene membranes [Grosgogeat et al., 1991]...

E. Grosgogeat, J.R. Fried, R.G. Jenkins and S.T. Hwang, A method for the determination of the pore size distribution of molecular sieve materials and its application to the characterization of partially pyrolyzed polysilastyrene/porous glass composite membranes. /. Membr. Sci., 57 (1991) 237. 

West et al. described the synthesis of polysilastyrene , a copolymer of dimethyldichlorosilane and phenylmethyldichlorosilane [46], the first polysilane which is soluble in organic solvents ... 

Polysilastyrene forms silicon carbide directly on heating up to 800 °C (10 K min ) with a ceramic yield of 30%, in contrast to polydimethylsilane where a polycarbosilane intermediate has to be isolated first. Since then. 

ACRONYM, ALTERNATIVE NAME PSS, polysilastyrene CLASS Polysilanes... 

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