Gstrein Chiara, Zhang Baozhong, Abdel-Rahman Mona Ahmed, Bertran Oscar, Alemán Carlos, Wegner Gerhard, Schlüter A Dieter
Laboratory of Polymer Chemistry , Department of Materials , ETH Zurich , Vladimir-Prelog-Weg 5 , 8093 Zürich , Switzerland . Email:
Centre of Analysis and Synthesis , Lund University , P.O. Box 124 , SE-22100 Lund , Sweden . Email:
Chem Sci. 2016 Jul 1;7(7):4644-4652. doi: 10.1039/c5sc04609b. Epub 2016 Apr 15.
Two series of dendronized polymers (DPs) of generations = 1-4 with different levels of dendritic substitution (low and high) and a solvatochromic probe at = 1 level are used to study their swelling behavior in a collection of solvents largely differing in polarity as indicated by the Kamlet-Taft parameters. This is done by measuring the UV-Vis spectra of all samples in all solvents and determining the longest wavelength absorptions (). The values fall into a range defined by the extreme situations, when the solvatochromic probe is either fully surrounded by solvent or completely shielded against it. The former situation is achieved in a model compound and the latter situation is believed to be reached when in a poor solvent the dendritic shell around the backbone is fully collapsed. We observe that solvent penetration into the interior of the DPs decreases with increasing and does so faster for the more highly dendritically substituted series than for the less highly substituted one. Interestingly, the swelling of the more highly substituted DP series already at the = 4 level has decreased to approximately 20% of that at the = 1 level which supports an earlier proposal that high DPs can be viewed as nano-sized molecular objects. Furthermore, when comparing these two DP series with a = 1-6 series of dendrimers investigated by Fréchet it becomes evident that even the less substituted series of DPs is much less responsive to solvent changes as assessed by the solvatochromic probe than the dendrimers, suggesting the branches around the (polymeric) core in DPs to be more densely packed compared to those in dendrimers, thus, establishing a key difference between these two dendritic macromolecules.
使用了两代（= 1 - 4）具有不同树枝状取代水平（低和高）且在 = 1 水平带有溶剂化显色探针的树枝状聚合物（DPs），来研究它们在一系列极性差异很大的溶剂中的溶胀行为，这些溶剂的极性由 Kamlet - Taft 参数表示。通过测量所有样品在所有溶剂中的紫外 - 可见光谱并确定最长波长吸收（）来完成此研究。这些值落入由极端情况定义的范围内，即溶剂化显色探针要么完全被溶剂包围，要么完全被屏蔽。前一种情况在模型化合物中实现，而后一种情况被认为是在不良溶剂中主链周围的树枝状壳层完全塌陷时达到。我们观察到，随着增加，溶剂向 DPs 内部的渗透减少，并且对于树枝状取代程度更高的系列，这种减少比取代程度较低的系列更快。有趣的是，在 = 4 水平时，取代程度更高的 DP 系列的溶胀已降至 = 1 水平时的约 20%，这支持了早期的提议，即高代 DPs 可被视为纳米尺寸的分子物体。此外，当将这两个 DP 系列与 Fréchet 研究的 = 1 - 6 代树枝状大分子系列进行比较时，很明显，通过溶剂化显色探针评估，即使是取代程度较低的 DP 系列对溶剂变化的响应也比树枝状大分子小得多，这表明与树枝状大分子相比，DPs 中（聚合物）核心周围的分支堆积更密集，从而确立了这两种树枝状大分子之间的关键差异。
