Silylene polymers

Poly(silylene) polymers are usually made by the reaction of diorganodichlorosilanes with sodium metal, in an inert diluent at temperatures above 100°C. (11.) Rapid stirring is ordinarily used so that the sodium is finely dispersed, speeding the rate of reaction. Either homopolymers or copolymers can be synthesized ... 

Ando and co-workers have reported the synthesis of a silyl-carborane hybrid diethynylbenzene-silylene polymer (108) (Fig. 66) possessing high thermal stability.136 The polymer contained Si and —C=C— group in the main chain and m-carborane and vinyl groups in the side chain. The 5% weight-loss temperature of the cured polymer in air was over 1000°C as determined by thermogravimetric analysis. 

Figure 66 The thermooxidatively stable silyl-carborane hybrid diethynylbenzene-silylene polymer 108 containing various carbon-carbon unsaturations. (Adapted from ref. 136.)...

Fig- 4. Chemical structure of the silyl-carborane hybrid diethynylbenzene-silylene polymer. 

The silyl-carborane hybrid diethynylbenzene-silylene polymer is prepared by a hydrosilylation reaction between diethynylbenzene-silylene polymer with the reactive vinyl side group and the 1,7-bis(dimethylsilyl)carborane group in toluene as solvent.The weight-average molecular weight of the polymer is determined to be 22,400 by using JASCO 802-SC gel permeation chromatography (GPC). The samples cured at 350 and 500° C are molded at 250°C for 6 min and pressed at 1795 kg/cm under vacuum for 30 s. 

Table 1. Characteristics of silyl-carborane hybrid diethynybenzene-silylene polymers...

Fig. 30. A scheme for thermosetting mechanism of silyl-carborane hybrid diethynylbenzene-silylene polymer by diene reaction between theC=C group and Ph-C=C group.

Fig. 32. 96.3 MHz a MQ/MAS NMR spectrum of silyl-carborane hybrid diethynybenzene-silylene polymer (A-1) in the solid state. The chemical shift (CS) axis and the quadrupolar induced shift (QIS) axis are drawn as described in the text.

Fig. 33. Isotropic projections of " B MQ/MAS NMR spectra of silyl-carborane hybrid diethynybenzene-silylene polymers (a) A-1, (b) A-2, (c) A-4, and (d) A-500.

Fig. 34. Boron Is core level X-ray photoelectron spectra of silyl-carborane hybrid dicthynybenzenc silylene polymers cured at various temperatures. 

The absorption spectra of silylene polymers and telomers have been extensively reported and it has been shown that the position of the absorption maximum shifts to the red with increasing degree of polymerization (6,15-19). We and others have reported the existence of narrow, line like fluorescence with no observed vibrational structure for a number of medium and high molecular weight polymers (2,9,16,20,22). The narrow, line-like fluorescence and the chain length dependence of the absorption spectra both indicate substantial delocalization of the electronic states involved in the transitions. 

Summary Carborane-hybridized silicon polymers were synthesized from the hydro-silylation reaction between diethynylbenzene-silylene polymers with reactive vinyl side groups and 1,7-bis(dimethylsilyl)carborane and l,7-bis(diphenylsilyl)carborane. Precise NMR spectroscopic studies show that the structures of these polymeres were quite complicated unreacted vinyl groups and pendant carborane substitution exist along with crosslinked carborane. These polymers show plastic moldability. Thermal treatment of the hybrid polymers gives excellent stability in both thermal and mechanical properties of the polymers. Their unreacted moieties seem to act as crosslinkable thermosetting features to make these polymers more stable. 

We have been studying non-siloxsine silicon polymers to obtain thermally stable and mechanically strong material. Ethynylene-silylene polymers have been found with excellent properties [8]. In addition, we have tried to introduce boron structures into silicon polymers to get further durability. 

While main chain strategies gave inefficient results, introduction of carborane to side chains is a relatively easy way to make hybrid systems. As Kunai reported, the versatile hydrosilylation reaction is the most reliable way to build hybrid polymers [9]. Reaction between diethynylbenzene-silylene polymers with reactive vinyl side groups 1 and l,7-bis(dimethylsilyl)carborane [HSi(CH3)2-(CBioH oC)SiH(CH3)2] 2a (R = CH3) in the presence of hydroplatinic acid catalyst gave carborane-hybridized silicon polymers 3a with 67 % yield (Scheme 1). GPC measurement of 3a provides a 21600 A/w vs. polystyrene standard, while the original polymer 1 had 6400. l,7-Bis(diphenylsilyl)carborane 2b (R = Ph) was also reacted with polymer 1 to get a similar hybrid 3b with a lower yield and Mfy, only 43 % and 5 800 respectively. Here hybrid silicon polymers with carborane side groups have been synthesized successfully. 

Lovinger, A.J., D.D. Davis, F.C. Schilling, F.A. Bovey, and J.M. Zeigler. 1989. Structures of poly(di-ethyl silylene) and poly(di-n-propyl silylene). Polym Comm 30 356. 

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