Fundamental Study on conservation treatment of water-logged wood with CO2

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Polyphenyleneoxide (PPO) is one of the important engineering plastics showing excellent mechanical, thermal, electrical and chemical properties at higher temperatures. In industry, PPO has been produced by oxidative-coupling reaction in toluene solvent and it has been pointed put that the solvent recovery plays an important role in determining the process feasibility. Additionally the viewpoint of green sustainable chemistry has brought the trend of solvent-free synthesis even for polymer industry.From these backgrounds, the synthesis of poly (phenylene oxide) (PPO) has been carried out in supercritical carbon dioxide (scCO_2) at 40 ℃ and 15 Mpa (one-step polymerization). The maximum yield and the weight-average molecular weight (Mw) of the synthesized PPO were ca. 70 % and 10,000 respectively. Two-step polymerization at 55 ℃, 22 Mpa or 70 ℃, 30 Mpa for 8 h was also tried successively after the synthesis at 40 ℃, 15 Mpa for 20 h, leading to increase the maximum yield and the Mw of the PPO up to ca. 80 % and 20,000 respectively. A small amount of diphenoquinone (DPQ) was produced as a by-product of PPO synthesis and its yield for the two-step polymerization was slightly larger (1.7 %) than that (ca.1.2 %) for one-step polymerization at 40 ℃ and 15 Mpa. The synthesized PPO was found to have similar glass transition temperature (T_g) of 200 ℃ to commercial one. These results indicated that the roles of ScCO_2 in this polymer synthesis were not only reaction solvent but also plasticizer for the polytmer, which allowed for us to progress the polymerization even after polymer-scCO_2 phase separation.