Silyl-carborane hybrid diethynylbenzene-silylene

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. 

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.

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. 

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