| Summary: | 碩士 === 國立清華大學 === 化學工程學系 === 94 === The self-assembly of amphiphilic copolymers into micelles in a selective solvent, including diblock copolymers, triblock copolymers and graft copolymers, have attracted much interest. Besides the mono-unimer composition, many investigations dealt with the multicomponent micelles (also called mixed micelles) from the di-diblock copolymer system, the tri-diblock copolymer system or the tri-triblock copolymer system because of their comicellization behavior and their extensive applications in such areas as drug delivery and particle modification.
The novel mixed micelle which was composed of graft copolymer and diblock copolymer is successfully prepared. Poly (N-isopropyl- acrylamide-co-methyl acrylic acid)-g-poly (D,L- lactide) (P(NIPAAm-co-MAAc)-g-PLA ) graft copolymer formed the multifunctional inner core of mixed micelle. PNIPAAm have lower critical solution temperature (LCST) at 32℃ which was below the nominal body temperature is unstable in the blood circulation. By the addition of MAAc in PNIPAAm, the LCST not only raise to above the nominal body, but also stabilize in blood circulation and offer the carboxylic group which can generate hydrogen bond interaction and dissociation at pH＞7.4. The micelle can utilized the pH and thermal response to accumulate at tumor tissue. Because the PLA is the side chain of graft copolymer, the mobility is very slowly so that the critical micelle concentration (CMC) is rarely low.
By addition the diblock copolymer poly(ethylene glycol)-b-poly (D,L-lactide) (PEG-PLA) in to the micelle system, PEG-PLA can avoid the secondary aggregation of graft copolymer because of the hydrophilicity of PEG.. It’s could not only reduce the secondary aggregation but also prolong the circulation time in the blood. In this study, we investigated the effect of mixed micelle with different hydrophobic length of diblock copolymer on comicellization. The results indicate that the stability of mixed micelles increases with the molecular weight of PLA increasing, and the hydrogen bond interaction of PEG and MAAc only occurred at initial aggregation during comicellization. The particle sizes of mixed micelle were ranged from100 to 200 and exhibited the narrow size distribution (PI < 0.1) in all of these cases.
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