Silyl-substituted polymers from

The synthesis of luminescent organoboron quinolate polymers (21) (Fig. 15) via a three-step procedure starting from a silylated polystyrene has been communicated. The synthesis was initiated by the highly selective borylation of poly (4-trimethylsilylstyrene) (PS-Si), followed by the replacement of the bromine substituents in poly(4-dibromoborylstyrene) (PS-BBr) with substituted thienyl groups (R = H, 3-hexyl, 5-hexyl). In the final step, the 8-hydroxyquinolato moiety was introduced. The hexyl-substituted polymers efficiently emitted light at 513-514nm upon excitation at 395 nm.40... 

The bulk polycondensation of (10) is normally carried out in evacuated, sealed vessels such as glass ampules or stainless steel Parr reactors, at temperatures between 160 and 220°C for 2-12 d (67). Two monomers with different substituents on each can be cocondensed to yield random copolymers. The by-product silyl ether is readily removed under reduced pressure, and the polymer purified by precipitation from appropriate solvents. Catalysis of the polycondensation of (10) by phenoxide ion in particular, as well as by other species, has been reported to bring about complete polymerization in 24—48 h at 150°C (68). Catalysis of the polycondensation of phosphoranimines that are similar to (10), but which yield P—O-substituted polymers (1), has also been described and appears promising for the synthesis of (1) with controlled structures (69,70). 

In the course of our studies of silyl-substituted carbodiimide polymers we first were concerned with materials derived from MeSiCb and SiCU [13-18]. However, it was found that many other silanes can be used to prepare non-oxidic gels (Table 1). 

Summary Reacting 2-neopentyl substituted silacyclobutanes la,b with MeLi/HMPA (hexamethylphosphoric triamide) anionic polymerization to give polymers 3a,b plays only a minor role for product formation. Instead, the head-to-head dimers 2a,b are isolated as main products. Their formation is explained by a complex reaction mechanism, in which various carbanionic, highly reactive intermediates are discussed. Obviously, the bis-a-silyl substituted carbanions 10a,b are remarkably stable, as can be concluded from Si NMR spectroscopic investigations at low temperature and from the products formed by trapping reactions with alcohols. 

ROMP polymers from silyl-substituted norbomadienes and norbornenes Hg, H2, N2, O2, C02 CH4, C2H0 85-167 22 0.1-1 [168]... 

The polymeric intermediate 2209a, derived, e.g., from substituted N,0-bissilyl-ated 4-aminobenzoic acids 2206 b or 2206 c and free or silylated terephthalic acid, affords, on heating to 180-200°C, the fire resistant polybenzoxazole (PBO) 2210 and H2O [20, 21] (Scheme 14.7). O-Silylated 2209b should, likewise, cyclize on heating to give the polymer PBO 2210 with formation of the volatile trimethylsila-... 

A series of silyl and disilyl substituted thioketene dimers (2,4-diylidene-1,3-dithietane), including polymers, have been synthesized (33, 34) [117]. HOMO-LUMO calculation by PM3 semi-empirical molecular orbital method predicted an intramolecular CT from the thioketene dimer to the Si-Si bond in disilyl thioketene dimer (33a) and no electronic interaction between the... 

The ability of fluoro-2 -phosphanes to transform silyl ethers into fluorides was first observed during a study of the reactions of phosphorus pentafluoride and its derivatives R PF5 (n = 1, 2, 3 R = hydrocarbon group) with trimethylsilyl ethers. Subsequently, this reaction was proposed as a new method for the preparation of C-F compounds from silyl ethers or silicic acid esters with fluoro-A -phosphanes. Pentafluorophenyl-substituted fluoro-A -phos-phanes were found to react similarily, Other workers found that tctrafluoro(phenyl)-A -phos-phane. which was chosen as the most convenient reagent with regard to reactivity and stability, gave considerable amounts of elimination products, especially with primary and cyclic alcohols. Good yields of fluorinated products are obtained when stable carbocations can be formed at the site of substitution, such as in tertiary alcohols, but 2-phcnylethanol. benzyl alcohol and diphcnylmethanol, on the other hand, give only poor yields of fluorinated products ethers and polymers are the main products. ... 

The above values were selected, in the case of polyacetylene, from averages taken from available experimental and theoretical structural data. For the halogenated chains, appropriate values were selected from the results of both ab initio and CNDO/2 molecular orbital calculations and from structural data available on small-molecule analogues. Due to the unavailability of structural data for the silylated analogues, values were taken from those used for polyacetylene (except, of course, for those bonds and angles associated with an X atom) so as to deduce the effect of the substitution alone without inclusion of concomitant structural modifications along the polymer backbone resulting from such substitutions. 

An attractive, although tentative, alternative would be an alkyl-substituted silylsilylene formed from the polymer chain. Two thermodynamically reasonable routes to such intermediates are possible. The first route (equation 4) involves 1,1-elimination to produce the silylsilylene directly. This route has a precedent in organosilane thermal processes (78, 79). The second route (equations 5a and 5b) involves rearrangement from a silene produced by the disproportionation (46, 80, 81) of two silyl radicals caused by bond homolysis. This type of rearrangement has also been described in the literature (82). The postulated silylsilylenes are also attractive intermediates to explain the rebonding of silicon to carbon atoms other than those in the original a positions (CH insertion), which is obvious from the mass spectral analysis of gaseous products from the laser ablation of isotopically labeled poly(di-n-hexylsilane). 

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