Study of the Cu[I]/Cu[II] catalytic system in 2,6-dimethylphenol polymerization to poly(phenylene oxide)

Abstract

• Oxidative polymerization of 2,6-dimethylphenol catalyzed by Cu[I] and Cu[II] systems, i.e. CuBr/dbeda, Cu 2 O/Br 2 /dbeda, CuBr 2 /dbeda and CuCO 3 /Br 2 /dbeda. • Starting with Cu[I] compounds, produces the most active catalytic systems. • Novel mechanism of poly(phenylene oxide) synthesis was presented. The study of Allan S. Hay catalytic systems containing copper[I] and copper[II] complexes, ie. CuBr/dbeda (where dbeda = N , N'-di-(t‑butyl)ethylenediamine), Cu 2 O/Br 2 /dbeda CuBr 2 /dbeda and CuCO 3 /Br 2 /dbeda in the polymerization of 2,6-dimethylphenol(2,6-DMP) to poly(phenylene oxide) (PPO) was presented. In the presence of bromine in the amount of 4.5 Br 2 /Cu, the copper[II] catalysts formed the greater number of polymerization centers. The values of the molar mass as well as its distribution depended on the 2,6-DMP/Cu molar ratio and the reaction time. Polymer with the higher molar mass was obtained at the molar ratio 2,6-DMP/Cu = 1000 and with the use of the copper[I] catalyst. By increasing the 2,6-DMP/Cu ratio to 1800, polymer with the lower molar mass was prepared. The reverse effect was observed for the copper[II] catalyst. The mechanism of 2,6-DMP polymerization to PPO was proposed in presence of the used catalysts. Also, the role of the bromine excess in the process was explained. In this mechanism the copper system Cu[I]⇄Cu[II] is responsible for the formation of oxygen and para -carbon radicals which are the starting molecules to launch the polymer synthesis. The "bromine" system reversibly provides the Br 2 molecule to brominate 2,6-DMP. The resulting 4‑bromo-2,6-dimethylphenol forms a carbon radical in the reaction with copper[I] complex.