The block copolymerization of 4,4-vinylphenyl-N,N-bis(4-tert-butylphenyl)benzenamine (A) with 2-(2-(4-vinylphenyl)ethynyl)pyridine (B) was performed using sec-butyllithium (s-BuLi) as an initiator in the absence and presence of potassium tert-butoxide (KOBut) in tetrahydrofuran (THF) at -78 degrees C. The block copolymerization was not successful in the absence of KOBut, whereas the well-defined diblock copolymer (poly(A-b-B)) containing pendent triphenylamine and ethynylpyridine was successfully synthesized in the presence of excess KOBut due to the change in the countercation from Li+ to K+ and the suppression of ion dissociation by the salt common effect. The poly(A-b-B)s had predictable molecular weights (M-n=4,900-20,000 g/mol) and narrow molecular weight distributions (M-w/M-n=1.13-1.15). In addition, the resulting block copolymer showed good solubility and excellent thermal properties. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4233-4239