Hybrid silicones synthesis

Fig. 11 Si NMR spectrum of the hybrid silicone synthesized from L H and precursor M with B(CgF )3 (from run 26, Table 3)...

Fig. 12 Mark-Houwitik-Sakaruda plots for commercial PDMS terminated by SiMe (black), PDMS synthesized with B(C j)j (grey), hybrid silicones synthesized with B(C j)3 (green from precursor H/ magenta from precursor M) (See also Plate 15 in the Colour Plate Section)...

Besides, the hybrid silicones synthesized nsing the method in Scheme 3 produced scattered linear lines, whereas those obtained from precursor M mostly overlap on a single line, with a y intercept lower than 0.2 units compared to the PDMS one. This difference is typical of the theoretical lower hydrodynamic volumes for cyclic structures, compared to linear ones [21, 22]. From this analysis, it is reasonable to conclude that the formation of macrocycles prevents high molar masses to be reached, since the hybrid silicones are not capable of ring scission through redistribution reactions within the macromolecular chains, unless PDMS chains. 

Use of Original Fluorinated Telomers in the Synthesis of Hybrid Silicones... 

Ameduri B, Boutevin B, Caporiccio G, Guida-Pietrasanta F, Ratsimihety A. Use of fluori-nated telomers in the preparation of hybrid silicones. In Hougham G, Davidson T, Cassidy P (Eds) Fluorinated Polymers Synthesis and Applications, Plenum, New York (in press)... 

Abstract This paper proposes new ways of preparation of hybrid silicones, i.e. an alternated multiblock seqnence of silicone and alkyl spacers, via a polycondensation process catalyzed by the tris(pentaflnorophenyl)borane, a water-tolerant Lewis acid, between methoxy and hydrogeno fnnctionalized silanes and siloxanes at room temperature and in the open air. The protocol was first developed with model molecules which led to polydimethylsiloxane (PDMS) chains, in order to seize the best experimental conditions. Several factors were studied such as the contents of each reactants, the nature of the solvent or the rate of addition. The best conditions were then adapted to the synthesis of hybrid silicones, condensing alkylated oligo-carbosiloxanes with methoxy or hydrogeno chain-ends and complementary small molecules. A systematic limitation in final molar masses of hybrid silicones was observed and explained by the formation of macrocycles, which cannot redistribnte or condense further while formed. 

Scheme 3 Synthesis of hybrid silicones starting from DMDMS...

The successful isolation of 1-silaallenes and 1-germaallenes raises the expectation of synthesis of a novel class of allenic compounds having an sp-hybridized silicon unit, that is, 2-silaallene derivatives. Although the generation of 2-silaallene (f-Bu)-CH2-CH=Si=CH-CH2-(t-Bu) was postulated in the reaction of (H2C=CH)2SiCl2 with 2-equivalent of t-BuLi, no distinct evidence on the generation of such a compound has been obtained so far. 

Since the first isolation of tetramesityldisilene by West et al. in 1981, a number of stable disilenes have been synthesized, and their structures and properties have been extensively investigated up to date [1,2]. However, known types of stable disilenes had been limited to simple acyclic derivatives with one Si=Si double bond until 1996, when the first stable cyclotetrasilene was synthesized [3]. Recently, the number of known skeletal types of disilenes has increased remarkably, and studies of their structures and reactions have made astonishing progress. The chemistry of disilenes is now approaching a stage to be compared with the extensive and profound chemistry of olefins. Here, we discuss the synthesis, structure, and reactions of novel cyclic and bicyclic disilenes and a trisilaallene, the first compound with a formally sp-hybridized silicon atom. 

Synthesis of Hybrid Silicones Starting from Bis-Silanol Monomers... 

One of the first hybrid bis-silanols that was used in the synthesis of hybrid silicones, and reported by Merker and Scott in 1964 [4], was bis-hydroxy(tetramethyl-p-silphenylene siloxane) L It was obtained via a magnesium route according to Scheme 4 ... 

Stern et al. [26] had pubhshed, in 1987, an article where they studied the structure-permeabihty relations of various sihcon polymers and which gave, among others, the Tg of several hybrid silicones - [(Me)2Si - R - Si(Me)20]x -, where R = - C2H4 - Celiu - CsHie -(TgS around- 90 °C), R = m-C6H4 -(Tg = - 48 °C) and R = p-CeH4 - (Tg = - 18 °C), but nothing was said about their synthesis. 

As a variant of this first method using Grignard reagents to prepare hybrid silicones, it may be cited a very recently published synthesis of poly(sil-oxylene-ethylene-phenylene-ethylene)s by reaction of a bis-chlorosiloxane with the bismagnesium derivative of a diethynyl compound [29,30] according to the following scheme ... 

During the year 1970, several articles were published by Kim et al. [41-46] about the synthesis and the properties of fluorinated hybrid silicone homopolymers and copolymers. These polymers were obtained by hydrosilylation of a, (D-dienes with chlorohydrogenosilanes, and the obtained bis-chlorosilanes were then hydrolysed into bis-silanols and polymerized or copolycondensed (R = R or R or R or R, Z = alkyl, aUcyl ether, fluoroalkyl, fluoroether, etc.) (cf. Scheme 19). 

Synthesis of Hybrid Silicones Through Hydrosilylation of cr, oi-Dienes. Hydrosilylation Polymerization... 

Scheme 1. Synthesis of carborane-hybridized silicon polymers 3.

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