| 학회 | 한국고분자학회 |
| 학술대회 | 2004년 봄 (04/09 ~ 04/10, 고려대학교) |
| 권호 | 29권 1호, p.39 |
| 발표분야 | 기능성 고분자 |
| 제목 | 초임계 유체 기술을 이용한 생분해성 고분자의 합성 |
| 초록 | Lactic acid derived from agricultural products by fermentation is nontoxic and harmless to animals, plants, and human beings. And, polylactides, the polymers of lactic acid have significant applications in the environmental and medical fields. However, stringent requirements must be fulfilled before a polymer can be used for biomedical applications. The purity of the polymer product is of concern, because residual monomers, catalysts, and solvents pose risks when such materials are in contact with biological fluids or tissues. The solution polymerization of L-lactide (L-LA) in regular hydrocarbon solvents, such as methylene chloride, chlorobenzene, benzene, or toluene, is not favored because these solvents must be thoroughly removed before use. In addition, when poly(L-lactide) (PLLA) is synthesized by the ring-opening polymerization (ROP) of L-LA, it is almost inevitable that the polymer obtained contains residual monomer, which was reported to enhance polymer hydrolytic degradation. In this respect, the production of polylactides under solvent-free conditions, combined with the possible extraction of residual monomer, by using proceses like the supercritical antisolvent (SAS) recrystallization process, shows great promise. Supercritical carbon dioxide (scCO2) is a viable ‘green’ alternative and can be removed without trace. Moreover, it has been demonstrated that scCO2 is a promising alternate reaction medium for polymerization. However, its widespread use has been restricted due to its limited solvent power, which reduces possible homogeneous polymerizations to an extremely narrow range. Thus far, most studies have focused on heterogeneous-phase polymerizations and on the development of new ‘CO2-philic’ materials (substance with a high affinity for CO2 solution at lower pressures). However, in many cases, solutions to the use of expensive ‘CO2-philic’ materials and their later removal are needed. A number of studies have reported upon the ROP of cyclic esters in scCO2. While an increase in yield and molecular weight (MW) in the presence of the stabilizer has been reported, all MWs obtained were lower than 50,000 g/mol. Recently, we found that supercritical chlorodifluoromethane (scR22) can be successfully utilized as a solvent for the ROP of L-LA, wherein the polymerization proceeds in a homogeneous state in scR22 and results in high PLLA molecular weights. The ring-opening polymerization of L-lactide initiated by stannous octoate was carried out in scR22 at various reaction conditions (time and temperature) and reactant concentrations (initiator, monomer, and solvent). The monomer conversion increased to ca. 70 % on increasing the reaction time to 1 h. The molecular weight of the PLLA product also increased to ca. 160 000 g/mol over the same period. Increasing reaction temperature from 90 to 130 ℃ resulted in increased monomer conversion and PLLA MW. A series of polymerizations conducted at various 1-dodecanol and stannous octoate concentrations suggested that stannous octoate does not act as an initiator by itself, and that the tin-alkoxide formed from 1-dodecanol and stannous octoate serves as the initiating species in scR22. While increases in monomer conversion and in the PLLA molecular weight were observed with increasing monomer concentration, the chlorodifluoromethane concentration had the opposite on both. After the polymerization, PLLA microspheres were prepared in situ by using a continuous supercritical anti-solvent process without residual organic solvent and monomer to yield highly purified microspheres for environmental and biomedical applications. |
| 저자 | 김수현1, 박현덕1, 이항수1, 백지원2, 박수영2, 이윤우2, 김영하1 |
| 소속 | 1한국과학기술(연), 2서울대 |
| 키워드 | biodegradable; poly(L-lactide); microsphere; ring-opening polymerization; supercritical fluid |
