Boron Main-Chain

In one of their notable examples, the hydroboration polymerization of low molecular weight allyl-telechelic polyisobutylene with tripylborane (trip = 2,4,6-triisopropylphenyl) was found to yield air-stable organoboron segmented block copolymers. These boron main-chain polymers (8) (Fig. 8), unlike the general ones, were stable to air. The stability was due to the steric hindrance of the bulky tripyl groups preventing oxygen attack of the borons.28... 

Many polymers containing boron in the main chain have been prepared but most of them have either been of low molecular weight or intractable cross-linked structures. Some interest has been shown in the tri-3-aminoborazoles, which polymerise on heating (Figure 29.15f. ... 

Wolfe and Wagener have developed main-chain boronate polymers (59) (Fig. 38) by the acyclic diene metathesis (ADMET) polymerization of symmetrical ,oj-dienes, containing both methyl- and phenyl-substituted boronate functionalities using Mo and Ru catalysts.84 The ring-opening metathesis polymerization (ROMP) of several norbornene monomers containing methyl- and phenyl-substituted boronates into... 

Conjugated boron polymers containing platimnn or palladium atom in the main chain were also prepared by hydroboration polymerization between tetrayne/ metal complex monomers and tripylborane (scheme 16).30 From gel permeation chromatographic analysis [THF, polystyrene (PSt) standards], the number-average molecular weights of the polymers obtained were found to be 9000. The polymers were soluble in common organic solvents such as THF, chloroform, and benzene. The absorption peaks due to tt-tt transition were observed around 390 nm in the UV-vis spectra of these polymers. The fluorescence emission spectra exhibited intense peaks at 490 nm in chloroform. 

Pu reported the synthesis of axially chiral-conjugated polymer 82 bearing a chiral binaphthyl moiety in the main chain by the cross-coupling polymerization of chiral bifunctional boronic acid 80 with dibromide 81 (Equation (39)). The polymer is soluble in common organic solvents, such as THE, benzene, toluene, pyridine, chlorobenzene, dichloromethane, chloroform, and 1,2-dichloroethane. The polymer composed of racemic 80 was also synthesized, and the difference of characteristics was examined. Optically active polymer 82 was shown to enhance fluorescence quantum yield up to = 0.8 compared with the racemic 82 ( = 0.5). Morphologies of the optically active and racemic polymers were also compared with a systematic atomic-force microscopy (AEM). 

It appears that apart from cyclonite, octogen (XI), a N-acetyl derivative (XXX) and a number of nitramines, mainly chain compounds, less stable than cyclonite, are also formed by this method, in side-reactions. Hence the cyclonite obtained has a relatively low melting point (190-195°C) and may be less stable than that prepared by other methods. The conduct of the reaction in the presence of boron fluoride reduces the number of by-products formed. 

Two poly(cyclodiborazane) polymers containing group-10 transition metal-acetylide groups P50 and P51 were prepared by Chujo et al. and represent a new kind of organometal-lic acetylide polymers functionalized with group-13 boron elements in the main chain.78 The structures of P50 and P51 were confirmed by IR and NMR ( H, 31P, and nB) spectra. The optical properties were studied by UV-vis absorption and emission measurements. It was shown that these polymers display extended -conjugation length via transition metal and boron atom with enhanced air- and moisture stability. 

Only boron in the third periodic group, and then, only as the element, occurs in the solid state as a polymer. With the boranes (borohydrides), main chain bonds are only partly boron-boron bonds they also possess boron-hydrogen-boron bond character. 

Although most p-CPs are p-type (electron donor) semiconductors, caused by introduction of borane in polymer backbone, making it electron deficient. By introducing boron in the polymer main chain, chujo showed that the p-conjugation length was extended via vacant p-orbital of... 

Sundararaman, A., M. Victor, R. Varughese, and F. Jakle. 2005. A family of main-chain polymeric Lewis acids Synthesis and fluorescent sensing properties of boron-modified polythiophenes. J Am Chem Soc 127 13748-13749. 

The introduction of polar-pyiidine moieties was achieved by the use of the appropriate monomer diol and more specifically 2,5-bis(4-hydroxyphenyl) pyridine, which combines the rigid oligo-phenyl main chain strucmre with the presence of polar pyridine groups. The monomer can be prepared using palladium-mediated cross coupling of 2,5- dibromopyridine with a properly protected boronic acid. ... 

Polymers Containing Boronic Acid in the Main-Chain... 

Tandem esterification of boronic acid-appended molecules with the appropriate diol molecules leads to formation of polymers with boronic ester linkages in the main chain. The three-dimensional tandem repeat from esterification forms covalent moleeular frameworks. Indeed, this type of polymeric materials is fascinating. Related discussions are exeluded from this chapter. 

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