Looped Structure of Flowerlike Micelles Revealed by 1H NMR Relaxometry and Light Scattering

被引:83
作者
de Graaf, Albert J. [1 ]
Boere, Kristel W. M. [1 ]
Kemmink, Johan
Fokkink, Remco G. [3 ]
van Nostrum, Cornelus F. [1 ]
Rijkers, Dirk T. S.
van der Gucht, Jasper [3 ]
Wienk, Hans [2 ]
Baldus, Marc [2 ]
Mastrobattista, Enrico [1 ]
Vermonden, Tina [1 ]
Hennink, Wim E. [1 ]
机构
[1] Univ Utrecht, Utrecht Inst Pharmaceut Sci, NL-3508 TB Utrecht, Netherlands
[2] Univ Utrecht, NMR Spect Res Grp, Bijvoet Ctr Biomol Res, NL-3584 CH Utrecht, Netherlands
[3] Wageningen Univ, Lab Phys Chem & Colloid Sci, NL-6700 EK Wageningen, Netherlands
关键词
BLOCK-COPOLYMER MICELLES; TRIBLOCK COPOLYMER; AQUEOUS-SOLUTION; POLY(ETHYLENE GLYCOL); DRUG-DELIVERY; AGGREGATION BEHAVIOR; NMR RELAXATION; OXIDE); MICELLIZATION; NANOPARTICLES;
D O I
10.1021/la2019605
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
We present experimental proof that so-called "flowerlike micelles" exist and that they have some distinctly different properties compared to their "starlike" counterparts. Amphiphilic AB diblock and BAB triblock copolymers consisting of poly(ethylene glycol) (PEG) as hydrophilic A block and thermosensitive poly(N-isopropylacrylamide) (pNIPAm) B block(s) were synthesized via atom transfer radical polymerization (ATRP). In aqueous solutions, both block copolymer types form micelles above the cloud point of pNIPAm. Static and dynamic light scattering measurements in combination with NMR relaxation experiments proved the existence of flowerlike micelles based on pNIPAm(16kDa)-PEG(4kDa)-pNIPAm(16kDa) which had a smaller radius and lower mass and aggregation number than starlike micelles based on mPEG(2kDa)-pNIPAm(16kDa). Furthermore, the PEG surface density was much lower for the flowerlike micelles, which we attribute to the looped configuration of the hydrophilic PEG block. H-1 NMR relaxation measurements showed biphasic T-2 relaxation for PEG, indicating rigid PEG segments close to the micelle core and more flexible distal segments. Even the flexible distal segments were shown to have a lower mobility in the flowerlike micelles compared to the starlike micelles, indicating strain due to loop formation. Taken together, it is demonstrated that self-assemblies of BAB triblock copolymers have their hydrophilic block in a looped conformation and thus indeed adopt a flowerlike conformation.
引用
收藏
页码:9843 / 9848
页数:6
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