Synthesis And Characterization Of Low-molecular-weight PPO In Water

Poly(2,6-dimethyl-l,4-phenylene oxide)(PPO) has excellent physical and electrical properties. However, high-molecular-weight PPO has some deficiency, such as high melt viscosity, poor processability and low reactivity when it is used as additive for coatings and composites. The low-molecular-weight PPO could be a good solution to the problems mentioned above, while maintaining almost all the advantages. Low-molecular-weight PPO is generally prepared via depolymerization of high-molecular-weight PPO in organic solution. However, the depolymerization reaction often encounters problems, such as bimodal polydispersity, and difficulty in controlling the exact molecular structure of PPO. The synthesis of low-molecular-weight PPO in water can solve those problems due to the relatively low reaction rate, and the use of water mediem accords with the view of green chemistry.Low-molecular-weight PPO with unimodal polydispersity was synthesized by oxidative polymerization of2,6-dimethylphenol (DMP) in the presence of Cu-EDTA catalyst in water. A series of low-molecular-weight PPO oligomers with Mn ranged from360to3500were obtained. It was found that the molecular weight and polydispersity were affected by reaction time, reaction temperature and catalyst concentration. Based on the detector response-elution volume curve and the molecular weight from GPC, a possible molecular weight growth mechanism was proposed. The structure and properties of low-molecular-weight PPO oligomers were characterized by atomic absorption spectroscopy, differential scanning calorimetry, Ubbelohde viscometer, nuclear magnetic resonance spectroscopy. Compared to the commercial low-molecular-weight PPO, PPO oligomers synthesized in water had a much lower residual copper content. The relationships between Tg and Mn at relatively low molecular weight are in good agreement with the equation proposed by Fox and Loshack.Through the copolymerization between DMP and3,3’,5,5’-tetramethyl bisphenol A (TMBPA), a,co-bisphenol PPO (PPO-2OH) oligomers with different molecular weight were obtained in water. Three structural isomers of PPO-2OH exist in the product, with TMBPA presented in the middle, penultimate and end of the PPO-2OH molecule. Different kinds of copolymerization bisphenols, surfactants and concentration, and the molar ratio of DMP/TMBPA could influence the oxidative copolymerization. a.w-Bismethacrylate PPO (PPO-2MC) oligomers were obtained based on the terminal modification reaction with PPO-2OH. The Tg of PPO-2MC was10℃lower than the parent PPO-2OH. Through thermal polymerization, PPO-2MC with different Mn could give rise to PPO networks having the same Tg with high-molecular-weight PPO.