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A New Route to Organoboron Polymers via Highly Selective Polymer Modification Reactions

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journal contribution
posted on 21.09.2004, 00:00 authored by Yang Qin, Guanglou Cheng, Obianuju Achara, Kshitij Parab, Frieder Jäkle
We have developed a highly efficient new method for the introduction of Lewis acidic boron centers into the side chains of organic polymers. Our methodology involves three steps:  (i) the controlled polymerization of the functional monomer 4-trimethylsilylstyrene (SSi), (ii) the exchange of the silyl groups in poly(4-trimethylsilylstyrene) (PSSi) with BBr3 to give the reactive polymer poly(4-dibromoborylstyrene) (PSBBr), and (iii) the fine-tuning of the Lewis acidity of the individual boron centers through substituent exchange reactions with nucleophiles. Treatment of PSBBr with ethoxytrimethylsilane and THF respectively yields the moderately Lewis acidic poly(arylboronate)s PSBOR (R = Et, 4-bromobutyl). The alkoxy groups in PSBOR have been exchanged with pinacol to form the air-stable polymer PSBPin (Pin = pinacolato). Treatment of PSBBr with 2-thienyltrimethyltin and pentafluorophenylcopper respectively gives the well-defined highly Lewis acidic triarylborane polymers PSBTh and PSBPf (Th = 2-thienyl, Pf = 2,3,4,5,6-pentafluorophenyl), which contain triarylborane moieties at every repeat unit along the polymer chain. All polymers have been studied by multinuclear NMR spectroscopy and differential scanning calorimetry. The molecular weights of the arylboronate polymers PSBOR have been determined by gel permeation chromatography, and the highly selective formation of polymer PSBPin has been confirmed by static light scattering.