Silyl carboranes

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.)...

Structural Characterization of Silyl-Carborane Hybrid Si-Based Polymer... 

The chemical structure of the silyl-carborane hybrid Si-based 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...

The multiple-quantum (MQ)/MAS NMR is one of the 2D NMR methods, which is capable of averaging out the second-order quadrupolar interaction in nuclei with spin > 1/2 such as H, "B, O, etc. The "B MQ/ MAS NMR measurements on boron as contained in silyl-carborane hybrid Si-based polymer networks considered here. The molded samples are cut into small pieces to insert them into a 4-mm NMR rotor and spun at 12 kHz in a MAS probe. The observation frequency of the "B nucleus (spin number I = 3/2 and isotope natural abundance = 80.42%) is 96.3 MHz. Excitation of both the echo (—3Q) and anti echo (+3Q) coherences is achieved by using a three-pulse sequence with a zero quantum filter (z-filter). The widths of the first, second, and third pulses are 3.0 4.1 ps, 1.1-1.6 ps, and 19-28 ps, respectively. The z-filter is 20 ps. The recycle delay time is 6-15 s and the data point of FI (vertical) axis is 64 and for each the number of scans is 144. Then, the total measurement time is 15-38 h. The phase cycling used in this experiment consists of 12 phases. Boron phosphate (BPO4 3 = 0 ppm) is used as an external standard for "B. The chemical shift value of BPO4 is —3.60 ppm from BF3 O(C2H5)2 which is used as a standard reference in " B NMR in the liquid state. The transmitter frequency of " B is set on peak of BPO4 for a trustworthy chemical shift after Fourier transform." " ... 

STRUCTURAL CHARACTERIZATION OF SILYL-CARBORANE HYBRID SI-BASED POLYMER NETWORK MATERIALS... 

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. 

Relationship between thermosetting structure and characteristics of a silyl-carborane hybrid Si-containing polymer network... 

FIGURE 26.20 A silyl-carborane hybrid diethynylbenzene-silylene polymer. 

Hideaki, K. Koichi, O. Motokuni, L Toshiya, S. Shigeki, K. Isao, A. 2003. Structural study of silyl-carborane hybrid diethynylbenzene-sUylene polymers by high-resolution sohd-state "B, C, and Si NMR spectroscopy. Chem. Mater., 15 355-62. 

Ichitani, M. Yonezawa, K. Okada, K. Sugimoto, T. 1999. Silyl-carborane hybridized diethynylbenzene-si-lylene polymers. Polym. 7., 31 908—12. 

The above silyl carboranes interact further with dilithiocarborane to form products having a six-membered ring incorporating two carborane nuclei. 

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