Li Xingfu, Kroeger Anja, Azzam Tony, Eisenberg Adi
Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec, H3A 2K6, Canada.
Langmuir. 2008 Mar 18;24(6):2705-11. doi: 10.1021/la702614x. Epub 2008 Feb 1.
The dendrimer concentration dependence of the supramolecular structure formation of polystyrene-block-poly(acrylic acid) in dioxane/THF was investigated as a function of water content. The distribution as well as the localization of the dendrimer units inside the formed aggregates were determined by comparative studies of turbidity measurements and transmission electron microscopy. The strong and specific interactions present between the amine groups of the dendrimer (PAMAM) and the carboxylic acid residues of PAA in the copolymer have a strong influence on the structure formation. The PAMAM concentration as well as the character of the terminal groups of the dendrimer influence the strength of these interactions and consequently affect the structure formation process. As shown by fluorescence quenching experiments, on all supramolecular hierarchical structure levels, and specifically in vesicles, the dendrimer is coated by the PAA chains of the block copolymer due to the strong interactions; since the PAA blocks are connected to the PS blocks, which form the corona, the dendrimer is surrounded by PS chains and is thus encapsulated into the hydrophobic regions of the block copolymer aggregates. A high-resolution transmission electron microscopy image of a micelle is shown, in which the individual dendrimer cores are seen to be localized in the center of these aggregates, and thus, the structure proposed in the previous publication (Kroeger, A.; Li, X.; Eisenberg, A. Langmuir 2007, 23, 10732) is confirmed. Furthermore, the sizes of the resulting aggregates depend on the relative concentration of dendrimer, expressed as RAm/Ac (the ratio of amine to acid groups). With increasing RAm/Ac values, not only the sizes of the micelles but also the vesicle dimensions, especially vesicle wall thicknesses, increase, and this effect suggests the encapsulation of the dendrimer into the vesicle walls. Thus, the constitution of the vesicle structure is determined precisely. This feature allows the potential incorporation of a wide range of species into the vesicle walls or the center of the micelle cores.
研究了在二氧六环/四氢呋喃中，树枝状聚合物浓度对聚苯乙烯-嵌段-聚丙烯酸超分子结构形成的影响，并将其作为水含量的函数进行研究。通过浊度测量和透射电子显微镜的对比研究，确定了树枝状聚合物单元在形成的聚集体中的分布以及定位。树枝状聚合物（聚酰胺-胺，PAMAM）的胺基与共聚物中聚丙烯酸（PAA）的羧酸残基之间存在的强特异性相互作用，对结构形成有很大影响。PAMAM的浓度以及树枝状聚合物末端基团的性质会影响这些相互作用的强度，从而影响结构形成过程。荧光猝灭实验表明，在所有超分子层次结构水平上，特别是在囊泡中，由于强相互作用，树枝状聚合物被嵌段共聚物的PAA链包覆；由于PAA嵌段与形成冠层的聚苯乙烯（PS）嵌段相连，树枝状聚合物被PS链包围，因此被封装在嵌段共聚物聚集体的疏水区域中。展示了一张胶束的高分辨率透射电子显微镜图像，其中可以看到单个树枝状聚合物核位于这些聚集体的中心，因此，先前出版物（Kroeger, A.; Li, X.; Eisenberg, A. Langmuir 2007, 23, 10732）中提出的结构得到了证实。此外，所得聚集体的尺寸取决于树枝状聚合物的相对浓度，用RAm/Ac（胺基与酸基的比例）表示。随着RAm/Ac值的增加，不仅胶束的尺寸增加，囊泡尺寸特别是囊泡壁厚度也增加，这种效应表明树枝状聚合物被封装在囊泡壁中。因此，囊泡结构的组成被精确确定。这一特性使得有可能将多种物质纳入囊泡壁或胶束核的中心。
