| 초록 |
Pluronic block copolymers (Pluronics) are produced on a commercial scale to enable wide range of novel applications from emulsification and colloidal stabilization as nonionic surfactants to nanotechnology and biotechnology as amphiphilic macromolecules. While the Pluronic block copolymers offer the advantages of being readily available for such applications, it contains different levels of low molecular weight (MW) “impurities” that would interfere with the self-assembly of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, triblock copolymers particularly in aqueous solutions. For example, the eluent gel permeation chromatography technique provided a strong evidence that commercially as-received samples of Pluronics contain the low MW impurities that do not participate in the micellization of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, triblock copolymers in water even at temperatures above critical micellization temperature. In this presentation, we will highlight two major advances in studying Pluronic block copolymers. First, we have developed a large scale (e.g. gram scale) purification technique by taking advantages of competitive adsorption between low MW impurities and triblock copolymers in solution. Adsorption-based HPLC technique was used to confirm that we can maintain the content of the low MW impurities less than 2 wt.% upon the large scale purification, while the as-received Pluronic samples can contain about 20 wt.% impurities. Second, we have investigated the impact of the low MW impurities on the micellar packing and solution phase behavior of Pluronic F108 and F127 samples. Small angle x-ray scattering experiments on as-received and purified Pluronics revealed that the inter-micellar distance depends not on the polymer concentration, but on the triblock copolymer concentration upon ordering into body-centered-cubic (BCC) and face-centered-cubic (FCC), when the Pluronic solutions develop ordered structures. In addition, the impurities made it difficult for the micelles to pack and form ordered structures. For example, compared to purified Pluronics, higher concentrations of Pluronic solution are needed for the as-received samples to develop the ordered structures in solution. |
