Poly -boronate

Poly(boronic carbamatejs were prepared by alkoxyboration polymerization of diisocyanates with mesityldimethoxyborane (scheme 33).59 The polymers obtained have boronic carbamate functions in their repeating units and can be expected to be novel reactive polymers. First, alkoxyboration polymerization between mesityldimethoxyborane and 1,6-hexamethylene diisocyanate was examined, and the optimized reaction conditions were bulk reactions at 140°C. Both aliphatic and aromatic diisocyanates gave the corresponding polymers. When aromatic diisocyanates were employed, the... 

Fibrous glass Poly(sulfur nitride) Poly(boron nitride) Silicon carbide... 

Mercurideboronations occur with gem-di- and -poly boronate esters, e.g. ... 

Diisocyanates have been shown to undergo haloboration-phenylboration pol5nnerization to give halosubstituted pol5nners (17) (75). They also undergo alkoxyboration in the presence of mesityldimethoxyborane to produce poly(boronic carbamates) (18) (eq. 18) (76). 

Boron-linked polymers are not rare. The most obvious include borosili-cate glasses and slime. However, these common materials rely primarily on borate as the key linking element and not boronic acids. Poly(boronate)s can be found in the literature as far back as the 1960s, and then, after a long drought, most progress has been made in the last decade. As seen with coordination... 

The earliest recorded poly(boronate)s were tri-coordinate systems based on phenylene-l,4-diboronic acid. Some of the first materials were not in fact esters... 

FIGURE 26. Covalent poly(boronate)s were first identified as (a) the borono-hydra-zone analogs before (b-e) ester linked materials were identified, (d and e) Phosphino-integrated poly(boronate)s display reactivity and structural motifs similar to the monomeric precursors. 

FIGURE 27. Poly(boronate)s using fluorene-diboronic acids with pentaerythritol (a) and 1,2,4,5-tetrahydroxybenzene (b) have shown to act as self-repairing materials (a and b) and as a new class of wide band-gap semiconductor (b). 

FIGURE 28. Diboronic acid bola-amphiphiles combined with alkyl tethered disaccharides form pH responsive poly(boronate)s in aqueous media. 

FIGURE 29. Ester formation coupled with intramolecular dative B-N bond formation has been used to create tetra-coordinate poly(boronate)s upon introduction of saccharides. 

Soluble boronate oligomers were prepared by dehydrogenation reactions of diols with thexylborane as shown in Scheme 8 (57). Bifunctional thexylborane was employed as a monomer, and dehydrogenation between diols and thexylborane was used to produce a poly(boronic ester). 

CHR) , formed, e g. from the reaction of diazomethane and alcohols or hydroxylamine derivatives in the presence of boron compounds or with metal compounds. Poly-methylene is formally the same as polyethene and the properties of the various polymers depend upon the degree of polymerization and the stereochemistry. 

Other typical pyrotechnic fuels include charcoal, sulfur, boron, siUcon, and synthetic polymers such as poly(vinyl alcohol) and poly(vinyl chloride). Extensive use has been made of natural products such as starches and gums, and the use of these materials continues to be substantial in the fireworks industry. MiUtary pyrotechnics have moved away from the use of natural products due to the inherent variabiUty in these materials depending on climatic conditions during the growth of the plants from which the compounds are derived. 

Inorganic Esters. Boric acid and borax form cycHc esters with poly(vinyl alcohol) (85—100). The reaction is markedly sensitive to pH, boric acid concentration, and the cation-to-boron ratio. An insoluble gel is formed at pH above 4.5—5.0 ... 

Fibers in which the basic chemical units have been formed by chemical synthesis, followed by fiber formation, are called synthetic fibers. Examples include nylon, carbon, boron fibers, organic fibers, ceramic fibers, and metallic fibers. Among all commercially available fibers, Kevlar fibers exhibit high strength and modulus. (Kevlar is a DuPont trademark for poly [p-phenylene diamine terephthalamide].) It is an aromatic polyamide (aramid) in which at least 85% of the... 

Kim and Webster [57] were the first to show that trifunctional benzene-based monomers can also be used to synthesize poly(phenylene)s, in this case hyperbranched structures 31 based on 1,3,5-trisubstituled benzene cores. They self-condensed l,3-dibromophenyl-5-boronic acid leading to the formation of soluble, hyperbranched PPP-type macromolecule 31. 

At about die same time, die application of the Suzuki coupling, the crosscoupling of boronic acids widi aryl-alkenyl halides in die presence of a base and a catalytic amount of palladium catalyst (Scheme 9.12),16 for step-growth polymerization also appeared. Schliiter et al. reported die synthesis of soluble poly(para-phenylene)s by using the Suzuki coupling condition in 1989 (Scheme 9.13).17 Because aryl-alkenyl boronic acids are readily available and moisture stable, the Suzuki coupling became one of die most commonly used mediods for die synthesis of a variety of polymers.18... 

The next step is the hydrogen reduction of the trichlorosilane (Reaction 2 above). The end product is a poly crystalline silicon rod up to 200 mm in diameter and several meters in length. The resulting EGS material is extremely pure with less than 2 ppm of carbon and only a few ppb of boron and residual donors. The Czochralski pulling technique is used to prepare large single crystals of silicon, which are subsequently sliced into wafers for use in electronic devices.1 1... 

Poly crystalline boron nitride films, with a structure similar to rhombohedral boron carbide and a ratio of boron to nitrogen of 3 1, were produced by hot-filament CVD. This work indicates the possible existence of other boron-nitride structures. 

The cubic UB, 2-type boride structure with space group Fm3m can be described on the basis of a B,2-cubooctahedron (see Fig. 1) . The association of the B,2-poly-hedra by oriented B—B bonds gives rise to a three-dimensional skeleton with boron cages. Formally, the arrangement of the B,2-units and of the metals atoms is of the NaCl-type. Each metal is located in the center of a B24-cubooctahedron. 

During the time of the Olin reports, the first examples of oligomeric boron-bridged (l-pyrazolyl)borate systems appeared from the laboratory of Trofimenko at DuPont Chemicals 24 He reported the synthesis of poly(l-pyrazolyl)borates (6) (Fig. 5) from the reactions of alkali metal borohydrides with the pyrazole ligand. The (l-pyrazolyl)borate ligand was obtained from two pyrazole units when bridged by a BR2 unit on one side and by a metal or onium ion on the other. Even though reports... 

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