Pnictogen bonding‐mediated controlled cationic polymerization of styrene derivatives: Catalytic activity investigation using non‐ionic and ionic pnictogen compounds

Abstract The cationic polymerization of p ‐methoxystyrene (pMOS) was carried out at 25°C using pMOS·HCl and Sb(C 6 F 5 ) 3 . Under the condition of [pMOS·HCl]:[Sb(C 6 F 5 ) 3 ]:[pMOS] = 10:10:500 in mM concentration, the polymerization in CH 3 CN/CH 2 Cl 2 (3/1 in volume ratio) homogeneously proceeded giving rise to poly(pMOS) with M n = 5800 and M w / M n = 1.50. Based on the monomer consumption rate, the catalytic activity was increased in the order of Sb(C 6 F 5 ) 3 (5.9 × 10 −1 h −1 ) > Te(C 6 F 5 ) 2 (2.0 × 10 −1 h −1 ) > IC 6 F 5 (1.0 × 10 −2 h −1 ). In the presence of n Bu 4 NCl (0.02 equivalent relative to Sb(C 6 F 5 ) 3 ), the molecular weight distribution became narrower ( M w / M n = 1.23), but the MALDI‐TOF/MS implied chain transfer reactions. On the other hand, the cationic polymerization of pMOS in CH 2 Cl 2 using [MeSbPh 3 ][TEPB] combined with n Bu 4 NCl resulted in better molecular weight controllability (calculated M n = 6100 and theoretical M n = 6300), where chain transfer reactions were decreased as confirmed by the MALDI‐TOF/MS analysis. [SbPh 4 ][TEPB] and [SbPh 4 ][OTf] exhibited a decreased catalytic activity. [EtOCOCH 2 SbPh 3 ][TEPB] with the electron‐withdrawing ester group showed the highest activity (monomer conversion reached 91% in 8 h) while maintaining narrow molecular weight distribution ( M w / M n = 1.27). p ‐Methylstyrene and styrene were also polymerized using catalyst [EtOCOCH 2 SbPh 3 ][TEPB], although the polymerization was not controlled.