Boron polymers formation

Covalent polymers with reversible properties arising from dynamic covalent bonds such as disulfide exchange reaction [47 9], transesterification [50,51], transetherification [52], and boronate ester formation [53] were reported without respect to DCC. These studies should involve DCLs in... 

For instance, poly(9-fluorenone) can be electropolymerized in boron trifluoride diethyl etherate (BFEE) media, while the polymerization takes place in CH2CI2IBU4NBF4, albeit with a much smaller rate, and polymer formation caimot be observed inacetonitrilelBu4NBF4, as seen in Fig. 4.3 [123]. 

Film devices are often developed based on polymer backbone or framework. For example, a poly-pyrrole film with borane in the backbone has been obtained by direct electropolymerisation. Boronic acid derivatised pyrroles have been employed to make molecular imprinted polymers (MIPs), for example for the detection of dopamine. Figure 8.8 shows the concept of polymer formation in the presence of analyte followed by extraction to provide highly selective pockets for dopamine to bind. The read-out in this case is based on the Fe(CN)/" redox probe. Poly-amino-boronic acid films without imprinting were employed for dopamine detection. Co-polymer sensor films based on poly(aniline-co-3-aminobenzeneboronic acid) and poly(acrylamidophenylboronic acid) have been reported. 

Assemblies relying on the dative B-N interaction in conjunction with boronate ester formation to form linear polymers have also been identified. Unlike the stepwise phenanthroline-boronate assembly, esterification coupled with ligation occurs simultaneously. In fact, it is likely that coordination... 

FIGURE 12. Coordinative linear polymers based on boronate ester formation result from (a) ditopic coordination of pyridyl boronic acids to bis-diol functionalized porphyrins and (b) through coordinative interactions between rhodoximes and 3-aminoboronic acid. 

Growing from simple polymeric assemblies, more complex structures arise from the interactions between polyvalent boronic acids interacting with poly-functional diols. These products may be dynamic, highly cross-linked polymer networks, analogous to slime. Alternatively, these assemblies have taken the form of highly ordered frameworks with persistent pores. Regardless of the degree of order inherent in these systems, the key assembly motif still relies on boronate ester formation. 

Boronate ester formation has proven to be a facile alternative to traditional polymer assembly, given the ease of synthesis and dynamie reversibility to afford error-checking mechanisms during synthesis. Compared to conventional supramolecular polymers, boronate-linked materials display enhanced stability. It is argued that boronate ester formation takes the best from both worlds. 

In Chapter 6, B. M. Rombo et al. delve into the formation of boronate-linked supramolecular architectures based on boronate ester formation—for example, small molecule diesters form supramolecular self-assemblies in the solid state based on a phenyl-boron-phenyl sandwich motif in which these small oligomers link together to generate macrocycles and other polymers. The polymeric macrocyclics and linear structures demonstrate self-repair capabilities and constitute a new class of wide band-gap semiconducting materials. Through the incorporation of polyvalent boronates, covalent organic frameworks are described, which create highly crystalline, porous network materials. 

Lahaye, M., Inizan, F., and Vigouroux, ). (1998) NMR analysis of the chemical structure of ulvan and of ulvan-boron complex formation. Carbohydr. Polym., 36,239-249. 

Bonding Agents. These materials are generally only used in wire cable coat compounds. They are basically organic complexes of cobalt and cobalt—boron. In wire coat compounds they are used at very low levels of active cobalt to aid in the copper sulfide complex formation that is the primary adherance stmcture. The copper sulfide stmcture builds up at the brass mbber interface through copper in the brass and sulfur from the compound. The dendrites of copper sulfide formed entrap the polymer chains before the compound is vulcanized thus hoi ding the mbber firmly to the wire. 

Most of the compounds in this class have been prepared from preexisting crown ether units. By far, the most common approach is to use a benzo-substituted crown and an electrophilic condensation polymerization. A patent issued to Takekoshi, Scotia and Webb (General Electric) in 1974 which covered the formation of glyoxal and chloral type copolymers with dibenzo-18-crown-6. The latter were prepared by stirring the crown with an equivalent of chloral in chloroform solution. Boron trifluoride was catalyst in this reaction. The polymer which resulted was obtained in about 95% yield. The reaction is illustrated in Eq. (6.22). 

There is great interest in developing molecular precursors for boron-nitrogen polymers and boron nitride solid state materials, and one general procedure is described in this report. Combinations of B-trichloroborazene and hexamethyldisilazane lead to formation of a gel which, upon thermolysis, gives hexagonal boron nitride. The BN has been characterized by infrared spectroscopy, x-ray powder diffraction and transmission electron microscopy. 

Boronic acids (69 and 70) (Fig. 45) with more than one boronic acid functionality are known to form a polymer system on thermolysis through the elimination of water.93 Specifically, they form a boroxine (a boron ring system) glass that could lead to high char formation on burning. Tour and co-workers have reported the synthesis of several aromatic boronic acids and the preparation of their blends with acrylonitrile-butadiene-styrene (ABS) and polycarbonate (PC) resins. When the materials were tested for bum resistance using the UL-94 flame test, the bum times for the ABS samples were found to exceed 5 minutes, thereby showing unusual resistance to consumption by fire.94... 

Two chemical approaches that involve nucleophilic substitution of the chlorine atoms attached to boron with linking reagents are reported in the literature. In both methods, the driving force is the formation of a stable by-product or one that can easily be stabilized. These substances contain chlorine. They can be distinguished by the number of steps, either one or two, required for preparing the polymer, starting from /i-chloroborazine. 

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