An efficient functionalization of aromatic main-chain polymers was established using a combination of iridium-catalyzed borylation of aromatic C–H bonds and the Suzuki–Miyaura coupling reaction. Comparative studies of various iridium catalysts and borylation reagents show that [Ir(OMe)(COD)]2 is significantly more active than [IrCl(COD)]2, and bis(pinacolato)diboron induces higher efficiency than pinacolborane. The regioselectivity of the borylation was investigated using model compounds that mimic the repeating unit structure of poly(arylene ether sulfone). The C–H bonds of the sulfone model compound were more reactive than those of the bisphenol model compound, and the borylation occurred preferentially at the meta position to the sulfone moiety owing to steric hindrance and electronic effects. The glass transition temperature of the borylated polymer increases with increasing concentration of pinacolboronic ester group. The pinacolboronic ester group could be conveniently converted to boronic acid [B(OH)2] and potassium trifluoroborate (BF3K), which could also serve as versatile reactive sites for the synthesis of a wide range of functionalized polymers via Suzuki–Miyaura couplings.