Chemical and physical properties of low-molecular-weight poly(2,6-dimethyl-1,4-phenylene oxide) (LMW-PPO) synthesized by peroxydisulfate and metal/non-metal catalysts

Abstract

Preparing low-molecular-weight poly(2,6-dimethyl-1,4-phenylene oxide) (LMW-PPO) with high thermal stability and satisfactory dielectric properties is a challenge. Herein, we reported two methods for synthesizing LMW-PPO using metal and non-metal catalysts. In the presence of Cu(II), PPO with an M_n of 6.0 × 10³ can be obtained with peroxydisulfate (PDS) as the oxidant. In the absence of Cu(II) catalysts, mesoporphyrin IX dihydrochloride or methylamine can also catalyze PDS to produce low-molecular-weight and metal-free PPO (M_n of 4.9 × 10³ or 4.6 × 10³). PDS not only mediates the oxidation of Cu(I) to Cu(II) with Cu(II) catalysts, which is an important step for binding phenolates to form LMW-PPO, but also abstracts H from DMP to give DMP radicals, which then polymerize to LMW-PPO in the absence of the Cu(II) catalysts. In addition, PDS can effectively break the long-chain PPO to give shorter PPO, thus effectively mediating the molecular weight of PPO. Additionally, the decrease in T_g values from 215 °C to 159 °C with decreasing M_n of PPO mediated by peroxydisulfate indicate its improved processability while maintaining high thermal stability (T_d5% = 427 °C–439 °C). The satisfactory dielectric properties of the PPO obtained using PDS and metal-free catalysts also imply its high potential to be used for insulating materials.