Development of Production of Functional Polymer Particles in Supercritical Carbon Dioxide

近年来，除了水之外，超临界二氧化碳（scCO_2）作为一种环保介质也受到越来越多的关注。使用scCO_2作为聚合介质具有以下几个潜在的优点：低成本、低毒性、易于介质的去除和再循环，并且在不改变介质组成的情况下，温度和压力的相对小的变化可以显著改变溶解度、粘度和极性。在过去的八年中，有关甲基丙烯酸甲酯（MMA）和苯乙烯等乙烯基单体在scCO_2中分散聚合的论文已陆续发表。一些含氟聚合物和聚二甲基硅氧烷（PDMS）基聚合物已被证实可溶于CO_2或亲CO_2，并已被用作胶体稳定剂，对在scCO_2中有效的胶体稳定剂的研究日益引起人们的兴趣。总的来说，pdms基聚合物可能比氟化聚合物具有优势，因为pdms基聚合物的价格要便宜得多，而且它们在常规有机溶剂中的溶解度使所获得的产品易于表征。本研究以pdms型偶氮引发剂为引发剂（引发剂+稳定剂），将MMA在scCO_2中分散聚合制备PMMA颗粒。在氨基丙基端部聚甲基丙烯酸甲酯作为胶体稳定剂的情况下，用甲基丙烯酸甲酯在scCO_2中分散聚合制备了PMMA颗粒。在scCO_2中，65℃，30 MPa, 24 h，不添加任何稳定剂，通过沉淀聚合法制备了聚二乙烯基联苯颗粒。考察了聚合起始速率对转化率、粉体流动性、混凝度/低分子量副产物的数量以及颗粒中乙烯基含量的影响。

Recently, in addition to water, there have been increasing interests in supercritical carbon dioxide (scCO_2) as environmentally favorable media. The use of scCO_2 as medium for polymerizations has several potential advantages : low cost, low toxicily, eases of medium removal and recycling, and marked variations of solubility power, viscosity and polarity by relatively small changes in temperature and pressure without altering medium composition. The papers describing the dispersion polymerization of vinyl monomers such as methyl methacrylate (MMA) and styrene in scCO_2 have been published in the past eight years. Some fluorinated polymers and poly(dimethylsiloxane) (PDMS)-based polymers have been identified as being soluble in CO_2 or CO_2-philic and have been used as colloidal stabilizers, and there has been increasing interest on the colloidal stabilizers which are effective in scCO_2. In general, PDMS-based polymers may have advantages over fluorinated polymers from the viewpoints that PDMS-based polymers are much less expensive and their solubility in conventional organic solvents makes the characterization of the products obtained easy. In this research, PMMA particles could be produced by dispersion polymerization of MMA in scCO_2 using PDMS-based azoinitiator as inistab (initiator + stabilizer). Production of PMMA particles by the dispersion polymerization of MMA in scCO_2 in the presence of amino propyl terminated PDMS as colloidal stabilizer was also succeeded.Moreover, polydivinylbiphenyl particles were produced by precipitation polymerization of divinylbiphenyl without any stabilizer in scCO_2 at ca. 30 MPa for 24 h at 65℃. The effects of initiation rate of polymerization on the conversion, the fluidity of powder, the degree of coagulation/ the amount of low molecular weight by-products, and the amount of vinyl groups in the particles were examined.