Hydroboration boron functionalized polymers

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... 

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]. 

The Inifer process developed by Kennedy can be used to functionalize vinyl monomers via a cationic route by initiating a polymerization with an alkyl halide-boron trichloride mixture R BCl. The termination by transfer to an alkyl halide leaves a halide-terminated polymer. This can be transformed to a hydroxyl terminal unit via the sequence (1) dehydrohalogenation, (2) hydroboration, and (3) oxidation and hydrolysis (Equation 5.24). These co-functional blocks may be coupled to form diblock copolymers using standard reaction techniques, e.g., diisocyanate will couple cohydroxy and co-amine blocks together. Direct reactions can also occur, and co-acid chlorides combine readily with co-hydroxy units. 

Unlike molecules containing electron-rich heteroatoms, boron compounds do not poison Ziegler-Natta or metallocene polymerization catalysts. Borane-containing olefin comonomers are therefore well suited to produce olefin copolymers while retaining good catalyst activity. The resulting polymers are suitable for subsequent conversion into a variety of functional groups. In principle, two approaches are possible (1) hydroboration of the terminal double bond (formed by typical chain transfer processes) of a preformed polyolefin, and (2) direct copolymerization of propylene or a 1-alkene with an alkenyl borane (Scheme 11.4). 

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