Boronate-functionalized polymers

Hartwig and Hillmyer have recently reported the Rh-catalyzed borylation of polyolefins to yield boronate-functionalized polymers (58) (Fig. 37) in a single step.83 The number-average molecular weight of the borylated polymer that was obtained at a B2pin2 polyethylethylene ratio of 0.3 was found to be the highest (Mn = 52,000 and PDI = 1.09) among the developed boronate-functionalized polyolefins. 

Figure 37 The boronate-functionalized polymer (58) obtained by the Rh-catalyzed borylation of polyolefins. (Adapted from ref. 83.)...

In the area of ion sensing, cation recognition by electrodes containing functionalized redox-active polymers has been an area of considerable interest. Fabre and co-workers have reported the development of a boronate-functionalized polypyrrole as a fluoride anion-responsive electroactive polymer film. The electropolymerizable polypyrrole precursor (11) (Fig. 11) was synthesized by the hydroboration reaction of l-(phenylsulfonyl)-3-vinylpyrrole with diisopinocampheylborane followed by treatment with pinacol and the deprotection of the pyrrole ring.33 The same methodology was utilized for the production of several electropolymerizable aromatic compounds (of pyrrole (12) (Fig. 11), thiophene (13 and 14) (Fig. 11), and aniline) bearing boronic acid and boronate substituents as precursors of fluoride- and/or chloride-responsive conjugated polymer.34... 

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... 

Within either of the polymer-rich phases, borate esters and diesters of the functional groups are assumed to form with the same association constants as observed for the independent functional groups in aqueous solution. The resulting equations simply describe the borate ester association constants as well as mass balances on boron and polymer-bound functional groups. Wise and Weber used the model to estimate association constants for the borate esters formed with the diols in PVA and to predict the gelation of PVA-borate solutions. As we have independently measured the association constants for the borate esters formed in this work, we have used the model to estimate the radius of gyration of the GP3 dendrimer and to predict both the boron speciation in borate/GP3 solutions and the efficacy of PAUF using these functional dendrimers. 

With these assumptions, the distribution of boron species (among boric acid, borate anion, borate esters, and borate diesters) reduces to a function of boron concentration, polymer concentration, radius of gyration and solvated volume fraction of a polymer unit, solution pH, and the association constants for the borate esters of the functional groups employed. 

Boron Mechanism. Boron functions as a flame retardant in both the condensed and vapor phases. Under flaming conditions boron and halogens form the corresponding trihalide. Because boron (rihalides are effective Lewis acids, they promote cross-linking, minimizing decomposition of the polymer into volatile flammable gases. These trihalides arc also volatile thus they vaporize into the (lame and release halogen which Ihen functions as a Maine inhibitor. 

This volume of the series focuses on the photochemistry and photophysics of metal-containing polymers. Metals imbedded within macromolecular protein matrices form the basis for the photosynthesis of plants. Metal-polymer complexes form the basis for many revolutionary advances occurring now. The contributors to many of these advances are authors of chapters in this volume. Application areas covered in this volume include nonlinear optical materials, solar cells, light-emitting diodes, photovoltaic cells, field-effect transistors, chemosensing devices, and biosensing devices. At the heart of each of these applications are metal atoms that allow the assembly to function as required. The use of boron-containing polymers in various electronic applications was described in Volume 8 of this series. 

Nevertheless, a few years ago, Kennedy 66 69) developed a method yielding co-functional polymers by cationic polymerization of vinyl monomers. The principle of the socalled inifer method is to kinetically favor transfer to the initiating species with respect to all other kinds of transfer reactions (especially the transfer to monomer). A typical initiating system is composed of an allyl or benzyl halide and boron trichloride BCl3. This mixture behaves like an alkenium tetrachloro-borate and readily initiates the polymerization of monomers such as isobutene or a-methylstyrene. The efficiency of the halide as a transfer agent depends on the lability of the C—Cl bond and on the molar ratio [RC1]/[BC13],... 

Using a different approach, the research gronps of Fabre and Freund have synthesized boronate-functionalized conjugated polymers, which serve as electrochemical sensors. For example, a conjugated redox-active film of polypyrrole (174) was electrodeposited onto a platinum electrode from acetonitrile solution. Addition of fluoride anions led to a new redox system that showed an anodic shift relative to polypyrrole itself, which was attributed to fluoride binding to the boronate group. A related poly(aniline boronic acid) (175) was also reported and studied for saccharide detection. " ... 

To improve the thermal durability and inflammability of the materials, we have been investigating organoboron structures to hybridize with silicon polymers. In this field, the preceramic character of the borazine structure [2] and its catalytic function for anti-oxidation [3] are already known. Lately Chujo reported hydroboration polymerization to obtain boron-based polymers [4]. 

Functional polymers in which boron-containing groups permit to tailor the physical and/or chemical properties of the materials (e.g., flame retardants, neutron capture/ sensor systems, reversible hydrogen storage, optoelectronic or biomedical applications)... 

The interaction of boronic acids with saccharides " and anions has been extensively investigated, and boronic acids have also been exploited in a range of applications as diverse as sensing and separation, " NMR (nuclear magnetic resonance) shift reagents, functional polymers for electrophoresis, and molecular self-assembled capsules and materials. 

Boronic acid-functionalized polymers have been widely studied in view of the construction of biomaterials based on the capability of boronic acid to precisely recognize saeeharides. The boronic acid moieties can be easily introduced into the polymer ehain mainly through free-radical polymerization techniques. One versatile vinyl monomer for this purpose is m-acrylamidophenylboronic acid. Numerous polymers have been synthesized from this monomer in combination with various vinyl... 

This section focuses on molecular recognition of small diol molecules by a series of boronic acid-functionalized polymers in most cases, the target molecule is glucose because of the need for a glucose-sensing system or an insulin delivery system. 

Related to boronie acid-functionalized polymers, end-functionalized polymers are intriguing because of the boron-diol reactivity of their ends. Boronic acid moieties can be selectively incorporated into the end of the... 

Although the first report on boronic acids was published in 1862, boronate affinity materials have not been extensively investigated until recently. In recent years, various boronate-functionalized materials, " such as macroporous monoliths, " " nanoparticles, and mesoporous materials, have been developed into important tools for the facile selective extraction of cis-diol-containing compounds. With these matrices, several important materials with teamed boronate affinity and boronate avidity as well as boronate affinity-based molecularly imprinted polymers have been prepared. 

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