Development of Production of Functional Polymer Particles in Supercritical Carbon Dioxide

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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.