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 (S-Si), (ii) the exchange of the silyl groups in poly(4-trimethylsilylstyrene) (PS-Si) with BBr3 to give the reactive polymer poly(4-dibromoborylstyrene) (PS-BBr), and (iii) the fine-tuning of the Lewis acidity of the individual boron centers through substituent exchange reactions with nucleophiles. Treatment of PS-BBr with ethoxytrimethylsilane and THF respectively yields the moderately Lewis acidic poly(arylboronate)s PS-BOR (R ) Et, 4-bromobutyl). The alkoxy groups in PS-BOR have been exchanged with pinacol to form the air-stable polymer PS-BPin (Pin ) pinacolato). Treatment of PS-BBr with 2-thienyltrimethyltin and pentafluorophenylcopper respectively gives the well-defined highly Lewis acidic triarylborane polymers PS-BTh and PS-BPf (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 PS-BOR have been determined by gel permeation chromatography, and the highly selective formation of polymer PS-BPin has been confirmed by static light scattering.