Polysilane polymers molecular weight

In this photopolymerization, various molar ratios of polysilane MMA are used 1 1, 1 5, 1 10, 1 20, 1 50. Similarly, in the graft photopolymerization, while the polymer molecular weights and the polymerization yields decrease, the relative... 

The polymerization of these monomers in THF solutions with a catalytic amount of butyllithium gave the corresponding amino-substituted polysilanes 15a-d in high yields. Although polysilanes 15a and 15b were insoluble, 15c was soluble in various organic solvents. Since the solid state Si NMR spectra of 15a and 15b were almost similar to that of 15c, the insoluble polymer 15a and 15b are also pure amino-substituted polysilanes. The molecular weight distribution of 15c was determined by gel permeation chromatography calibrated by polystyrene standards with toluene as eluent Mn = 2.7 x 10", Mw n = 1.7. 

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. 

Polymerization ofiVIasked Disilenes. A novel approach, namely, the anionic polymerization of masked disilenes, has been used to synthesize a number of poly(dialkylsilanes) as well as the first dialkylamino substituted polysilanes (eq. 13) (111,112). The route is capable of providing monodisperse polymers with relatively high molecular weight M = lO" — 10 ), and holds promise of being a good method for the synthesis of alternating and block copolymers. 

Dehydrogenative Coupling of Hydride Functional Silanes. The autocouphng of dihydridosilanes was first observed usiag Wilkinson s catalyst (128). A considerable effort has been undertaken to enhance catalyst turnover and iacrease the molecular weight of polysilane products (129) because the materials have commercial potential ia ceramic, photoresist, and conductive polymer technology. 

Molecular weights of polysilane polymers depend upon the exact method of synthesis, as well as the purity of the dichlorosilane starting materials. Bimodal molecular weight distributions are commonly reported, as shown in Figure 1, but under some conditions... 

We have been recently studying new pathways leading to polysilanes with low polydispersity and controlled structures. Our research is focused on three areas. The first one is low temperature reductive coupling in the presence of ultrasound. This leads to monomodal polymers with molecular weights in the range from Mn=50,000 to Mn=300,000 and polydispersities as low as Mw/Mn=1.20 (in addition to usually formed cyclic oligomers). 

GPC traces of poly(phenylmethylsilylenes) prepared in the ultrasonication bath are shown in Fig. 1. In contrast to thermal condensation, monomodal high molecular weight polymer is formed. Oligomeric cycles (mostly cyclic pentamer), formed usually in high yield (cf. Table 1), can be very easily separated from the reaction mixture by precipitation with isopropanol. The molecular weight of polysilanes decreases and polydispersity increases with temperature. 

The discovery that soluble high molecular weight polysilanes may be prepared by the reductive coupling of dichlorodialkylsilanes by alkali metals (1,2) has led to considerable work on the properties of this interesting class of polymers (3,4,5). The preparation of the polymers leaves much to be desired as frequently the high polymer is only a minor product. Mechanistic studies of the reaction with a view to improving the relevant yields have been few (6). The major ones by Zeigler (7,8,9) showed that a silylene diradical was not involved in the reaction, and stressed the importance of polymer solvent interactions. 

The conformational mobility of a chromophoric main-chain polymer is often connected to its electronic structure. Therefore, changes in the UV-visible absorption spectra and/or chiroptical properties are spectroscopically observable as thermo-, solvato-, piezo-, or electrochromisms. It is widely reported that o-conjugating polysilanes exhibit these phenomena remarkably clearly.34 However, their structural origins were controversial until recently, since limited information was available on the correlation between the conformational properties of the main chain, electronic state, and (chir)optical characteristics. In 1996, we reported that in various polysilanes in tetrahydrofuran (THF) at 30°C, the main-chain peak intensity per silicon repeat unit, e (Si repeat unit)-1 dm3 cm-1, increases exponentially as the viscosity index, a, increases.41 Although conventional viscometric measurements often requires a wide range of low-dispersity molecular-weight polymer samples, a size exclusion chromatography (SEC) machine equipped with a viscometric detector can afford... 

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