Ring-opening polymerization polysilanes

Ring-Opening Polymerization. As with most other inorganic polymers, ring-opening polymerization of cyclotetrasilanes has been used to make polysilanes (109,110). This method, however, has so far only been used for polymethylphenylsilane (eq. 12). Molecular weights (up to 100,000) are higher than from transition-metal catalyzed polymerization of primary silanes. 

Suzuki, M. Kotani, J. Gyobu, S. Kaneko, T. Saegusa, T. 1994. Synthesis of sequence-ordered polysilane by anionic ring-opening polymerization of phenylno-namethycyclopentasilane. Macromolecules 27 2360-2363. 

Sakurai, H. Yoshida, M. Synthesis of Polysilanes by New Procedures Part 1 Ring-opening Polymerizations and the Polymerization of Masked Disilenes. In Silicon-based Polymers The Science and Technology of their Synthesis and Application-, Jones, R. G., Ando, W., Chojnowski, J., Eds. Kluwer Dordrecht, 2000 pp 375-399. 

Synthesis of Polysilanes. The most commonly utilized method is based on the Wurt/ type alkali metal coupling or dichlorosilanes. Other synthesis methods include dehydrogenative coupling, ring-opening polymerization, polymerization of masked disilenes. electrochemical synthesis, and polymer modification. 

Polysilanes with high stereoregularity have not yet been obtained. Partially stereoregular polysilanes have, however, been synthesized by the ring-opening polymerization of stereoisomeric (PhSiMe)4, as described in Section 5.3.5.33... 

H. Sakurai and M. Yoshida, Synthesis of polysilanes by new synthetic procedures Ring opening polymerizations and the polymerization of masked disilenes , in Reference 4, pp. 375 -400. 

Fig. 4 Approaches to the synthesis of polysilane block copolymers by living polymerization techniques (a) via anionic polymerization of masked disilenes (b) via anionic ring-opening polymerization of cyclotetrasilanes...

There are several reports in recent literature on the application of silicon-containing compounds as the initiators of cationic ring-opening polymerization. This apparently is related to the attempts to prepare block copolymers containing polysiloxane or polysilane segments. (CfL SiCFAgClCL system was used to initiate cationic polymerization of tetrahydrofuran... 

Polysilanes have been the first class of precursors used to prepare silicon carbide ceramics. In all cases, on pyrolysis, polysilanes are converted into polycarbosilanes by a Kumada rearrangement prior to the formation of an amorphous silicon carbide network. Several synthetic routes including dehydro-polymerization, ring-opening polymerization of strained cyclosilanes, polymerization of masked disilenes, or base catalyzed disproportionation reactions of disilanes have been described to prepare linear or branched polysilanes but despite its drawbacks the Wurtz-coupling route remains the method applied most, especially to prepare linear polysilanes. 

Besides the Wurtz-coupling reaction, other synthetic routes towards non-branched polysilanes have been reported, which overcome the drawbacks of polymodal molar weight distribution and low yield of the high molar mass fraction. However, so far the application of these routes has been very limited. The anionic ring opening polymerization of the strained 1,2,3,4-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane leads to poly(methylphenylsilane) in high yield but the starting cyclotetrasilane has to be prepared in three steps from diphenyldichlorosilane via octaphenylcyclotetrasilane [84] ... 

Keyword Polysilanes / Cyclosilanes / Photolysis / Ring-Opening Polymerization... 

Sakuiai H, Yoshida M (2000). Synthesis of polysilanes by new procedures Part 1 Ring-opening polymerizations and polymerization of masked disilenes. In Jones RG, Ando W, Chojnowski J (eds) Silicon containing polymers. Kluwer Academic, Dordrecht, pp 375-399... 

Some topics involving polymerizations and related chemical reactions which were covered at the "Silicones and Silicone Modified Materials" symposium are conversions from silicon itself to semi-inorganics (contribution by Lewis), ring-opening polymerizations (contributions by Chojnowski, Soum, Kress, Jallouli, and Komuro), atom-transfer radical polymerizations (Matyjaszewski), hydrosilation polymerizations (Kaganove, Tronc, Narayan-Sarathy), polymerizations with controlled stereochemistry (Kawakami), condensation polymerizations (Fu), and polysilane syntheses (Newton) (25). 

Modern Synthetic and Application Aspects of Polysilanes 2.2.3 Ring Opening Polymerization of Silacycles... 

Strained silacycles can be used in a ring opening polymerization (ROP) to yield linear polysilanes. 

As the ring opening polymerization of masked disilenes seems to occur in a strict head to tail fashion, highly ordered polysilanes have been obtained showing two sharp signals in the Si-NMR spectrum indicating a completely syndiotactic polymer [34, 35]. 

Because the electronic properties of polysilanes are dependent on the conformation of the backbone,which may depend on the configuration of the substituents, it is necessary to prepare polymers with well-defined microstructures. In ring opening polymerization, the resulting polymer microstructure depends on two factors. The fust one is the configuration of the substituents in the cycfic monomers. The second factor is the mechanism of die ring opening polymerization. This paper is mainly focused on the discussion of stereochemistry in the cyclotetrasilanes. 

Ring opening polymerization of la was attempted with both the monosilyl and disilyl cuprates. The monosilyl cuprate was used unsuccessfully to initiate polymerization, however, use of the disilyl cuprate resulted in nearly quantitative conversion to monomodal polymer with polydispersities in the range of Mw/Mn = 1.5. The polymerizations were carried out in THF at room temperature, which is interesting in itself, because if the polymerizations using BuLi are carried out in THF there is rapid decomposition of the polymer to five and six-membered cyclic polysilanes, however, with the silyl cuprates, the formation of cyclics is not observed, even after 24 hours. 

The remarkable electronic behavior of these materids has stimulated considerable effort to develop selective syntheses of polysilanes with well-defined structure. Typical synthetic procedures include the Wurtz coupling of dichlorosilanes,(5-5) anionic polymerization of masked disilenes, (9-72) anionic ring-opening polymerization of strained cyclosilanes,(i5-i7) electrochemical reduction of chlorosilanes,(75-27) and transition metal catalyzed dehydrogenative coupling of phenylsilanes (eq. l).(22-55)... 

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