| 학회 | 한국고분자학회 |
| 학술대회 | 2005년 봄 (04/14 ~ 04/15, 전경련회관) |
| 권호 | 30권 1호, p.453 |
| 발표분야 | 의료용 고분자 부문위원회 |
| 제목 | Effect of Temperature on the Mobility of Core-Shell Type Polymeric Nanoparticles Composed of Poly(γ-benzyl L-glutamate) and Poly(N-isopropylacrylamide) |
| 초록 | Introduction Polymers which show phase transition in water when the temperature is raised above a critical point, termed lower critical solution temperature(LCST), have attracted much attention in many areas of science and engineering. Among these polymers, poly(N-isopropylacrylamide) (PNIPAAm) is the most popular temperature sensitive polymers due to its dramatic and reversible transition behavior at around 32℃. Most of the work on the phase transition of PNIPAAm has so far been limited to measurements on the macroscopic quantities, though many methods including cloud point measurement, light scattering, DSC, and fluorescence have been used. NMR relaxation times and a linewidth give useful information about the microscopic molecular motion of polymer in solutions.1,2 In this work, instead of PNIPAAm, itself, we focus our study on the change of chain mobility of PNIPAAm segment as the shell of the core-shell type micelles during a temperature-induced phase transition. For this purpose, core-shell type temperature sensitive nanoparticles composed of poly(γ-benzyl L-glutamate(PBLG) as the core and PNIPAAm as the shell were prepared. Experimental PBLG/PNIPAAm diblock copolymers(abbreviated GN) were prepared by the ring-opening polymerization of γ-benzyl L-glutamate N-carboxyanhydride using amine-terminated PNIPAAm as a polymeric initiator. The contents of PNIPAAm in GN diblock copolymers and the molecular weights of those were determined by 1H-NMR spectroscopy. Subsequently, GN nanoparticles were prepared by firstly dissolving the GN diblock copolymer (0.03 g) in the mixture of 10 ml of THF/DMF (3/7: v/v). The resulting solution was then dialyzed against distilled water using cellulose membrane bag (molecular weight cut off of 12000~14000) for 24 h at room temperature. To demonstrate the micellar structure of the GN nanoparticle, this sample (3 mg) was dissolved in CDCl3 and D2O (1 ml), respectively, and 1H-NMR spectra were measured using 500 MHz spectrometer. Experimental measurements of spin-lattice relaxation times (T1) were performed on a Bruker AVANCE 400 NMR spectrometer by using the standard inversion recovery method with [π-τ-π/2Acq (FID)] pulse sequence in temperatures ranging from 25 to 40 ℃, and the line half-width of the 1H peak measured. Furthermore, the morphology of GN nanoparticles was assessed by TEM, and then change in the particle sizes with temperature was also investigated using an ELS. Results Change in the mobility of PNIPAAm shell in micelle-like GN nanoparticle in D2O during a temperature-induced phase transition could be detected by the measurement of spin-lattice relaxation times (T1) and line half-width in the temperature range from 25 to 40 ℃. The spin-lattice relaxation times (T1) of PNIPAAm decreased with increasing content of PBLG in PBLG/PNIPAAm nanoparticle, which means the dynamic behavior of PNIPAAm is restricted by incorporation of the PBLG segment. Interestingly, the dynamic states of N-isopropyl groups in D2O and CDCl3 were contrary to each other, beside, those of the N-isopropyl groups of PNIPAAm and the benzyl groups of PBLG in CDCl3 were contrary to each other, too. The morphology of GN nanoparticles was spherical, and the particle sizes increased with increasing content of PBLG and decreased with increasing temperature. References 1. Okada, R.; Matsukawa, S.; Watanabe, T. J. Molecular Strucrure 2002, 602-603, 473. 2. Tokuhiro, T.; Amiya, T.; Mamada, A.; Tanaka, T. Macromolecules 1991, 24, 2936. |
| 저자 | 유미경1, 장미경2, 나재운2, 조종수1 |
| 소속 | 1서울대, 2순천대 |
| 키워드 | core-shell type nanoparticle; LCST; mobility; spin-lattice relaxation times |
