Macromol. Chem. Phys. 18/2015

Abstract

Front Cover: The first protic‐acid‐free oxygen‐oxidative polymerization of diphenyl disulfide to yield poly(1,4‐phenylene sulfide), catalyzed by a vanadyl complex and a borate compound, is accomplished. Triphenylmethylium tetrakis(pentafluorophenyl)borate, having a non‐coordinating anion, is especially effective for the polymerization. Catalysis by the tetrafluoroborate salt is established at elevated temperatures where the anion is found to be less coordinative. Further details can be found in the article by F. Aida, S. Yamaguchi, Y. Takatori, K. Nagamatsu, D. Kiyokawa, K. Oyaizu,* and H. Nishide,* on page 1850.

Enhanced catalytic activity of oxovanadium complexes in oxidative polymerization of diphenyl disulfide

“…These results demonstrated the first catalysis of the oxidative polymerization of the disulfide by VO(salen) which has so far been regarded as inactive, suggesting that the electrochemical reversibility persisted at elevated temperatures as a result of the inertness of the salen 2− ligand to give rise to the positive shift of the formal potential for the [VO(salen)] 0/+ couple. The polymer obtained by this method was generally linear without branching or crosslinking as evidenced by the presence of only two carbon signals in the CP-MAS spectrum corresponding to the structural symmetry and the IR peak at 820 cm −1 ascribed to the C-H out-of-plane vibration of adjacent two hydrogens in the 1,4-phenylene unit, 10,17,19 suggesting the highly selective catalysis by VO(salen) (see the ESI †). The present study is the first achievement of catalytic activity of VO(salen) for the polymerization of the disulfide, while the catalytic mechanism of the vanadyl catalyst has so far been determined with the complexes bearing the inert salen 2− ligand and yet the catalytic activity has so far been obtained only for those having labile acac − and related ligands.…”

“…19 Even for the oxidative polymerization with quinones, strong acids were found to be essential for stabilizing the key intermediate, the sulfonium cation (PhS (PhSSPh) + ). 19 In the case of utilizing a VO(salen)-acid catalytic system, bromanil similarly accelerated the oxidative polymerization (entries 6 and 7). These results gave insight into the nature of the catalysis which was dominated by the oxidation of the monomer and much improved by placing a second redox couple to enhance the overall reactivity under moderately elevated temperature conditions to yield PPS with a higher molecular weight than those with the conventional catalyst system.…”

“…Strong acids or borate compounds, such as CHF 2 CF 2 SO 3 H and TrB(C 6 F 5 ) 4 , were essential to activate the vanadyl compounds. 19 Even for the oxidative polymerization with quinones, strong acids were found to be essential for stabilizing the key intermediate, the sulfonium cation (PhS (PhSSPh) + ). 19 In the case of utilizing a VO(salen)-acid catalytic system, bromanil similarly accelerated the oxidative polymerization (entries 6 and 7).…”

“…During the polymerization, the anionic species, such as the reduced forms of the quinones or the conjugated bases of strong acids, were reported to stabilize the cationic species, typically the sulfonium cations. 19 Bromanil turns out to be an anionic species by reduction, so the reduced bromanil might be able to form complexes with the cationic vanadyl compounds. It may be suggested that the effective enhanced catalytic systems of the vanadyl-acidbromanil triad was ascribed to the re-oxidation of the possibly newly formed complex between the vanadyl catalyst and the reduced bromanil.…”