Poly methylsilane

Characterization, Characterization work at all stages of fiber processing, as illustrated in Figure 1, is important. The discussion in this chapter will be limited to certain aspects of polymer and ceramic fiber characterization, which will be illustrated with poly(methylsilane) (MPS) and HPZ polymers and the ceramic fibers derived from these polymers. 

The slight solubility of the poly(methylsilane) was sufficient enough to effect GPC investigations. The molecular weight distribution vs. polystyrene standard showed a relatively uniform chain length of fifteen Si units. Poly(phenylsilane) was completely insoluble, which made GPC analysis impossible, but calculations on base of elemental analysis yielded a chain length of more than 20... 

From the present study, it is clear that methylsilane can be easily polymerized to poly(methylsilane), using either DMT or DMZ as catalyst. By proper choice of conditions, a polymer completely soluble in common organic solvents can be obtained, but prolonged reaction eventually leads to insoluble gel. As will be described elsewhere, this cross-linking reaction is of some advantage when the polymers are used as precursors for synthesis of silicon carbide. 

Figure 2. The UV Spectra of Poly(n-propyl-methyl-co iso-propyl-methylsilane) Copolymers vith Similar Molecular Weights Having the Following Compositions (1) 75/25, (2) 50/50 and (3) 25/75.

Figure 5. 67 MHz Carbon-13 NMR Spectra for Poly(n-propyl-methylsilane). (a) Proton Decoupled (b) Proton Coupled.

Figure 9. Change in UV Absorbance for Poly(phenyl-methyl-co-n-propyl-methylsilane) Copolymers at Their Respective 1MX as a Function of UV Exposure Time.

During photolysis, the double bond content of the polysilane(P-l)(15mol% in this experiment) decreased to 10mol%, as measured by 1H-NMR spectroscopy. However, the ratio, quantum yield of scission(Q(S))/quantum yield of crosslinking(Q(X)), was not affected by the reaction of the double bond. West and his coworkers have reported that poly((2-(3-cyclohexenyl)-ethyl)methylsilane-co-methylphenylsilane) crosslinked upon irradiation(55). The difference between our results and West s may lie in the amount of the double bond and inhibitation of the radical closslinking by the phenol moiety. Polysilane with a halogen moiety, P-8, photodecomposed rapidly, compared with P-1 or P-3. The introduction of a chloride moiety was effective for the sensitization of the photodegradation. Similar results has already been reported(55). 

The reductive cleavage of just one C-S bond yields the mono(lithiomethyl)silanes. This transformation is well known and used in the Peterson olefmation for the preparation of (lithiomethyl)trimethylsilane (15) [5], We employed it as a method to exchange the thiophenyl-group in the (phenylthiomethyl)silanes 5-14 with lithium, thus creating the corresponding poly(lithiomethyl)silanes (see, e.g.. Scheme 3 for methylsilanes) [4]. 

The quantum yields for scissioning ( >g) and crosslinking ( ) were determined for some representative polysilane derivatives both in solution and in the solid state (8). In all cases polymer scission is the predominant process and the values ranged from 0.2 to 1.0. For two cases, poly (methyl phenylsilane) and poly(cyclohexyl methylsilane) which were also examined in the solid state, the quantum yields were reduced by at least an order of magnitude from the solution values. 

Figure 4. Photochemical bleaching of a film of poly(cyclohexyl methylsilane) upon irradiation at 313 nm. (Reproduced with permission from Ref. 26. Copyright 1984 The International Society for Optical Engineering.)...

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