Santini Catherine M B, Hatton T Alan, Hammond Paula T
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Langmuir. 2006 Aug 29;22(18):7487-98. doi: 10.1021/la060341b.
The solution behavior of spherical dendrimers as well as hybrid-linear dendritic diblock copolymers has been extensively studied, and the size, shape, and ability of these polymers to encapsulate small molecules have led to their comparison with traditional micelles. We have recently reported the synthesis of a new dendritic copolymer architecture, the linear-dendritic rod diblock copolymer, and in this work, we examine the solution behavior of these unique polymers in methanol at 25 degrees C, using dynamic light scattering and intrinsic viscosity measurements. The diblock copolymers consist of a linear poly(ethylene oxide)-poly(ethylene imine) diblock copolymer backbone around which poly(amido amine) branches have been divergently synthesized from the poly(ethylene imine) block. The hydrodynamic radii and the viscometric radii of the polymers were found to increase slowly with increasing generation up to generation 3.5; however, after generation 3.5, the radii were found to increase very rapidly. This increase can be explained by an elongation of the dendritic block into a more rodlike configuration and a corresponding breakdown of the spherical approximation used to calculate the radii. The intrinsic viscosity of the amine and ester terminated polymers was found to follow two very different trends at low generation; however, at higher generations, they followed similar, yet slightly different, curves with the values for the amine terminated polymers only a little larger than those of the ester terminated polymers. At low generations, the chemistry of the end groups and its interaction with the solvent were found to be more important, whereas at higher generations, the highly branched nature of the dendritic block was the more important factor. For the ester terminated polymers, a maximum in the intrinsic viscosity occurred at generation 1.5. Since this maximum occurred at a much lower generation number than is traditionally seen for spherical dendrimers, new scaling relations for the intrinsic viscosity of dendritic rod polymers were developed and were found to support this observation. A minimum in the intrinsic viscosity was also observed at generation 3.5 for the ester terminated polymers and a minimum or leveling off in the intrinsic viscosity at generation 4.0 was found for the amine terminated polymers, which can be attributed to the transitioning of the polymers to a more elongated, rodlike shape and the increased influence of the shape factor on the intrinsic viscosity.
球形树枝状大分子以及杂化线性树枝状二嵌段共聚物的溶液行为已得到广泛研究，这些聚合物的尺寸、形状以及包封小分子的能力使其可与传统胶束进行比较。我们最近报道了一种新型树枝状共聚物结构——线性 - 树枝状棒状二嵌段共聚物的合成，在这项工作中，我们使用动态光散射和特性粘度测量方法研究了这些独特聚合物在25℃甲醇中的溶液行为。二嵌段共聚物由线性聚（环氧乙烷） - 聚（乙烯亚胺）二嵌段共聚物主链组成，围绕该主链，聚（酰胺胺）支链已从聚（乙烯亚胺）嵌段发散合成。发现聚合物的流体动力学半径和粘度半径随着代数增加到3.5代时缓慢增加；然而，在3.5代之后，半径增加非常迅速。这种增加可以通过树枝状嵌段伸长为更棒状的构型以及用于计算半径的球形近似的相应破坏来解释。发现胺端基和酯端基聚合物的特性粘度在低代数时遵循两种非常不同的趋势；然而，在较高代数时，它们遵循相似但略有不同的曲线，胺端基聚合物的值仅比酯端基聚合物的值略大。在低代数时，端基的化学性质及其与溶剂的相互作用更为重要，而在较高代数时，树枝状嵌段的高度支化性质是更重要的因素。对于酯端基聚合物，特性粘度在1.5代时出现最大值。由于这个最大值出现在比传统球形树枝状大分子低得多的代数处，因此开发了树枝状棒状聚合物特性粘度的新标度关系，并发现其支持这一观察结果。对于酯端基聚合物，在3.5代时也观察到特性粘度的最小值，对于胺端基聚合物，在4.0代时发现特性粘度最小值或趋于平稳，这可归因于聚合物转变为更细长的棒状形状以及形状因子对特性粘度的影响增加。
