Yi-Fang Lu,Song-Hai Wu,Cong Wang,Yong Liu,Fu-Gen Huang,Bao-Dong Song,Xu Han
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 Mn 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 (Mn 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 Tg values from 215 °C to 159 °C with decreasing Mn of PPO mediated by peroxydisulfate indicate its improved processability while maintaining high thermal stability (Td5% = 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.
Ya-Qi Wang,Qing He,Zhi-Yang Zhang,Lei Zhang,Na-Juan Yuan,Yong Liu,Hai-Tao Ren,Xu Han
Although the low molecular weight poly(2,6-dimethyl-1,4-phenyl oxide) (LMW-PPO) has been extensively applied in the field of 5G communication, the complicated procedures involved in the synthesis of LMW-PPO and efficient recovery of the homogeneous catalysts are still challenging nowadays. In this study, five ionic liquids (ILs) have been successfully synthesized, and LWM-PPO is directly synthesized using different Cu(OAc) 2 -ILs complexes as catalysts. Among them, Cu(OAc) 2 - IL(a) not only exhibits the high yield of LWM-PPO (83.68%, M n =3.6✕10 3 ) with the low 3,3’,5,5’-tetramethyl-4,4’-diphenoquinone (DPQ) yield (0.12%) and polydispersity index (PDI, 1.39) in methanol, but also maintains high stability after being recycled for 5 times. In addition, with increasing H 2 O contents in the system from 1.0% to 5.0%, the M n values of PPO decrease from 2.9✕10 3 to 2.4✕10 3 with the narrow PDI values in the range of 1.22-1.45, indicating that trace H 2 O effectively promotes the formation of binuclear Cu(II) complex between Cu(OAc) 2 ·H 2 O and ILs, which then polymerizes 2,6-dimethylphenol (DMP) to LMW-PPO. The synthesized LMW-PPO exhibits high thermostability ( T d5% =427.07-430.52°C), low glass transition temperature ( T g =167.6-180.3°C), and low dielectric constant ( D k =2.14-2.64, 1 GHz) and dielectric loss ( D f =2.83✕10 -3 -4.91✕10 -3 , 1 GHZ), indicating that it is more appropriate to be used in the field of 5G communication. This study provides new insight on the importance of ILs in direct synthesis of LMW-PPO with high performances.
危险品化学品经营许可证（带存储）