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

聚苯醚(PPO)是一种重要的工程塑料，在较高温度下具有优异的力学、热、电和化学性能。工业上多以甲苯为溶剂，通过氧化偶联反应生产PPO，指出溶剂回收率是决定工艺可行性的重要因素。在这种背景下，在超临界二氧化碳(SCCO_2)中，聚苯醚(PPO)的合成在40℃、15 Mpa(一步聚合)条件下进行。合成的PPO的最大产率约为70%，重均相对分子质量(MW)约为10,000。合成后在55℃、22 Mpa或70℃、30 Mpa下进行两步聚合，在40℃、15 Mpa下反应20 h，最大产率和相对分子质量分别提高到80%和20,000左右。在40℃和15 Mpa条件下，二步聚合的产率(1.7%)略高于一步聚合的产率(1.2%)。合成的聚苯醚的玻璃化转变温度(Tg)与商用聚苯醚的玻璃化转变温度(Tg)相近，为200℃。这些结果表明，SCCO_2在聚合物合成中的作用不仅是反应溶剂，而且是聚合物的增塑剂，使我们即使在聚合物-SCCO_2相分离后仍能进行聚合。

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.