Polysilylenes Polysilanes

Polysilylenes are chains, rings and 3D network polymers of silicon that contain the Si-Si bond in the polymer backbone. The tetravalency of silicon is generally completed with hydrogen or organic (aliphatic or aromatic) moieties. The basic structural unit of a polysilylene has formula 1. 

Dendrimeric products can also be formed through dehydrogenative coupling. These materials exhibit multidirectional a conjugation and show good electrical conductivity. These materials have also been used as negative-type photoresists because their exposure to air or light yields insoluble products. 

Several research groups have developed electrochemical polymerization of 

The molecular weights of polysilylenes (see Table 1) depend on the method of synthesis and the substituents on silicon. Although size-exclusion chromatography (SEC) may be used to estimate molecular weight and polydispersity, more accurate values of M , and radius of gyration (RG) are obtained from light-scattering 

The structure of polysilylenes has also been explored with H, and NMR methods. The studies indicate that polysilylene chain configurations in solution are varied and quite complex for a wide range of asymmetrically substituted homopolymers and copolymers. Thus, at high field (500 MHz) the alkyl protons in poly(methyl-n-hexylsilylene) are well resolved and assigned using 2D spectra. The spectra provide information about the microstructure and the Si spectra appear sensitive to stereochemical configuration at least to the pentad level. 

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Polysilylenes (polysilanes) (34b) have received widespread interest. Their electronic properties are associated with a-electron conjugation in the silicon backbone which allows a significant delocalization of electrons along the chain. In the usual synthesis of polysilylenes, diorganodichlorsilanes (34a) are treated with sodium metal in a hydrocarbon diluent [173]. In order to recreate the surface of the sodium metal permanently ultrasound is used in these reactions [174,175]. 

Polysilanes (or polysilylenes) consist of a silicon-catenated backbone with two substituents on each silicon atom. The two groups attached to the silicon chain... 

The history and development of polysilane chemistry is described. The polysilanes (polysilylenes) are linear polymers based on chains of silicon atoms, which show unique properties resulting from easy delocalization of sigma electrons in the silicon-silicon bonds. Polysilanes may be useful as precursors to silicon carbide ceramics, as photoresists in microelectronics, as photoinitiators for radical reactions, and as photoconductors. 

Polysilanes (or polysilylenes) consist of a silicon-catenated backbone with two substituents on each silicon atom (Structure 1). The groups R and R attached to the silicon chain can be of a large variety. Polysilanes with alkyl and/or aryl substituents have been the most thoroughly investigated [1-3], whereas polysilanes having at least a heteroatom substitution such as H, Cl, OR, NR2 have received much less attention [4]. The number of silicon atoms is usually from several hundreds to several thousands. 

The polysilanes oi polysilylenes (25), an unusual class of inorganic polymers, saw a very intense period of investigation during the 1980s. 

Polysilylenes and polygermylenes (also described as polysilanes and poly-germanes) are linear a-bonded Si or Ge polymers that contain a variety of C-based pendant groups. For charge transport, the role of the pendants is secondary and transport occurs by hopping between ordered main-chain segments between 15 to 30 repeat units separated by disordered links (Abkowitz and Stolka, 1988, 1988a, 1996). 

Excited state dynamics have been measured in polysilane by ultrafast techniques and site selective fluorescence studies made with polysilylenes. ... 

The chemistry of the polysilane (polysilylene) high polymers is undergoing rapid development. These polymers have unique photophysical properties of intrinsic scientific interest and are acquiring technological applications in several areas. Poly(silylenes) were reviewed in 198610, and several useful chapters on polysilanes appear in a recent monograph83. 

Polysilanes (alternative denotations polysilylenes, poly-catena-silicons) of the general structure shown in Chart 7.11 exhibit an absorption band in a relatively long-wavelength region, i.e. between 300 and 400 nm, reflecting the cr-conjuga-tion of electrons in the silicon chain. 

Polysilanes (or polysilylenes) are usually prepared by the Wurtz-type couphng reaction of dichlorodialkylsilanes or, alternatively, via a transition metal-catalyzed dehydrogenation of dialkylsilanes both approaches often exhibit difficulties in terms of controlling the molecular weight and chain-structure, however. Nonetheless, by using masked silylene monomers (l-phenyl-7,8-disilabicyclo[2.2.2]octa-2,5-dienes), a series of novel, well-defined linear poly(silylene)s (M /Mn 1.3) was successfully obtained via an anionic ROP (Scheme 5.11) [147-150]. 

The preparation of soluble polysilylenes by the condensation of dialkyldichlorosilanes with sodium was first described by West et al. (1). The polymer was found to have many interesting properties, and to be of potential commercial interest (2-4). This method of preparation is of general utility, although it has some shortcomings particularly in regard to the variety of polymeric species produced. There have been several studies on the reaction (5-11), with several suggestions to improve the yield. Alternate routes to polysilylenes have also been described (12,13), but these will not be considered here, except for one. This exception is the polymerization of some cyclic polysilanes, which was found to occur in the course of this work. 

Polysilanes (polysilylenes) consist of a linear chain of silicon atoms carrying two substituents, generally, either allqrl or aryl.(l,2,3) Interest in these materials stems from their unique properties, such as sigma-catenation and thermochromic behavior. They have potentid applications as photoresists, electro-optical devices, non-linear optical mateikls, and also as precursors to silicon carbide. 

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