Polybenzyl

Polybenzyls polyphenethyls Parylenes (poly-p-xylylene) Fusible, soluble, and stable at 400°C (752°F) low molecular weight. Melt above 520°C (968°F) insoluble capable of forming films poor thermal stability in air stable to 400-525° C (752-977°F) in inert atmosphere. 

Polybenzyl, Nitrated. See Vol 2, B95-R under Benzyl Chloride and Derivatives and Addnl Ref C.S. Marvel, OSRD 875 (1942)... 

A two-component plugging material [1763] consists of an aqueous suspension of bentonite clay powder (20% to 25%), ground chalk (7% to 8%), sulfanol (0.10% to 0.15%), and carboxymethylcellulose (1.0% to 1.5%) as the first component. This solution is pumped into the formation. A gel is formed if diluted hydrochloric acid is pumped down and mixes with the first component. The hydrochloric acid is inhibited with a mixture of alkyl-polybenzyl pyridinium chloride and urotropin. 

Related Polymer Systems and Synthetic Methods. Figure 12A shows a hypothetical synthesis of poly (p-phenylene methide) (PPM) from polybenzyl by redox-induced elimination. In principle, it should be possible to accomplish this experimentally under similar chemical and electrochemical redox conditions as those used here for the related polythiophenes. The electronic properties of PPM have recently been theoretically calculated by Boudreaux et al (16), including bandgap (1.17 eV) bandwidth (0.44 eV) ionization potential (4.2 eV) electron affinity (3.03 eV) oxidation potential (-0.20 vs SCE) reduction potential (-1.37 eV vs SCE). PPM has recently been synthesized and doped to a semiconductor (24). 

A possible synthesis of poly(p-phenylene methine) from polybenzyl via redox elimination (A). The two limiting structures of polyaniline (B). 

The chloride is usually (but not always) stabilised in storage by addition of aqueous alkali or anhydrous amines as acid acceptors. A 270 kg batch which was not stabilised polymerised violently when charged into a reactor. Contact of the chloride (slightly hydrolysed and acidic) with rust led to formation of ferric chloride which catalysed an intermolecular Friedel-Craft reaction to form polybenzyls with evolution of further hydrogen chloride. Contact of unstabilised benzyl chloride with aluminium, iron or rust should be avoided to obviate the risk of polycondensation. See Benzyl bromide Molecular sieve... 

BINAP core-functionalized dendrimers were synthesized by Fan et al. (36), via condensation of Frechet s polybenzyl ether dendritic wedges to 5,5 -diamino-BINAP (26—28). The various generations of BINAP core-functionalized dendrimers were tested in the ruthenium-catalyzed asymmetric hydrogenation of 2-[p-(2-methyl-propyl)phenyl]acrylic acid in the presence of 80 bar H2 pressure and in a 1 1 (v/v) methanol/toluene mixture. As later generations of the in situ prepared cymeneruthe-nium chloride dendritic catalysts were used, higher activities were observed (TOF values were 6.5, 8.3, and 214 h respectively). Relative to those of the BINAP... 

Liu et al. 43) prepared chiral BINOL ligands bearing dendritic Frechet-type polybenzyl ether wedges ((J )-41-(J )-44), which were assessed in enantioselective Lewis acid-catalyzed addition of Et2Zn to benzaldehyde. 

Benzyl acetate was prepared by addition of benzyl chloride (containing 0.6% pyridine as stabiliser) to preformed sodium acetate at 70°, followed by heating at 115°, then finally up to 135°C to complete the reaction. On one occasion, gas began to be evolved at the end of the dehydration phase, and the reaction accelerated to a violent explosion, rupturing the 25 mm thick cast iron vessel. This was attributed to presence of insufficient pyridine to maintain basicity, dissolution of iron by the acidic mixture, and catalysis by ferric chloride of a Friedel-Craft type polycondensation reaction to polybenzyls, with evolution of hydrogen chloride, which at 130°C would produce an overpressure approaching 100 bar. Previously the chloride had been supplied in steel drums containing 10% sodium carbonate or 3% sodium hydroxide solutions as... 

The synthesis of conformationally constrained bicyclic and tricyclic compounds, obtained via 5-Exo-Trig iodocyclisation of polybenzylated sugars with an allylic substituent at the anomeric position, is described. The conformation of these molecules has been studied by n.O.e. experiments and Molecular Dynamics calculations. The introduction of an amino and a carboxylic group resulted in the formation of conformationally constrained bicyclic glyco-aminoacids that mimic protein turn conformation. 

We took advantage of this observation in order to effect selective debenzylations, once an allylic appendage is attached to the sugar. For example, when the polybenzylated allyl-C-glucopyranoside 7 (10) is treated with iodine in THF at 0 °C, the bicyclic compound 8 is obtained (85 15 in favor to the 2 R isomer), which upon treatment with zinc and acetic acid undergoes a reductive elimination affording the C-glucoside 9 selectively deprotected at C-2. (11)... 

Preliminaiy results indicate that the polybenzylated azasugar 28 can be converted into the bicyclic derivative 29 (Figure 4), by treatment with N-iodosuccinimmide in THF at room temperature, taking advantage of the allylic appendage. In this reaction a single stereoisomer is obtained, the stereochemistry of which has still to be elucidated. 

Regioselective O-debenzylation. Of a number of Lewis acids, SnCl4 or TiCf, is the most effective for this reaction with polybenzylated sugars. The substrate... 

The synthesis of polybenzyls by carbenium ion intermediates has been summarized in several reviews [27,28]. Polybenzyls obtained from the polymerization of benzyl chloride are amorphous, highly branched polymers [29] (Fig. 12). 

One exception to the amorphous structure has been reported [30]. Crystalline polybenzyl was obtained from the low temperature (- 125° C) polymerization of benzyl chloride. However, the reaction was difficult to reproduce [31,32]. Consequently this procedure is not an effective method for the synthesis of linear polybenzyls. The usual amorphous, highly branched structure is formed as a result of a lack of positional selectivity and multiple substitution of the arene rings. Similar polymeric structures are obtained upon the polymerization of other nonsubstituted benzyl halides and benzyl alcohol [29]. The highly branched structure is a consequence of the involvement of benzyl carbenium ions in the Friedel-Crafts reaction. Benzyl substituents activate the monosubstituted phenyl groups toward further benzylation reaction. However, monomers containing alkyl substituents that sterically hinder substitution at the ortho position have been polymerized to linear polybenzyls. For example, the following... 

Figure 12 Example of typical polybenzyl structure obtained by the polymerization of benzyl chloride. (From Ref. 28.)...

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