Dutertre Fabien, Bang Ki-Taek, Vereroudakis Emmanouil, Loppinet Benoit, Yang Sanghee, Kang Sung-Yun, Fytas George, Choi Tae-Lim
Institute of Electronic Structure and Laser, FO.R.T.H, PO Box 1527, 71110 Heraklion, Greece.
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, U.K.
Macromolecules. 2019 May 14;52(9):3342-3350. doi: 10.1021/acs.macromol.9b00457. Epub 2019 Apr 23.
Well-defined dendronized polymers (denpols) bearing high-generation dendron are attractive nano-objects as high persistency provides distinct properties, contrast to the random coiled linear polymers However, their syntheses via graft-through approach have been very challenging due to their structural complexity and steric hindrance retarding polymerization. Here, we report the first example of the synthesis of poly(norbornene) (PNB) containing ester dendrons up to the sixth generation (G6) by ring-opening metathesis polymerization. This is the highest generation ever polymerized among dendronized polymers prepared by graft-through approach, producing denpols with molecular weight up to 1960 kg/mol. Combination of size-exclusion chromatography, light scattering, and neutron scattering allowed a thorough structural study of these large denpols in dilute solution. A semiflexible cylinder model was successfully applied to represent both the static and dynamic experimental quantities yielding persistent length ( ), cross-sectional radius ( ), and contour length (). The denpol persistency seemed to increase with generation, with reaching 27 nm (Kuhn length 54 nm) for PNB-G6, demonstrating a rod-like conformation. Poly(endo-tricycle[4.2.2.0]deca-3,9-diene) (PTD) denpols exhibited larger persistency than the PNB analogues of the same generation presumably due to the higher grafting density of the PTD denpols. As the dendritic side chains introduce shape anisotropy into the denpol backbone, future work will entail a study of these systems in the concentrated solutions and melts.
带有高代数树枝状结构的结构明确的树枝状聚合物（树枝状高分子）是引人注目的纳米物体，因为其高持久性赋予了独特的性质，这与无规卷曲的线性聚合物不同。然而，由于其结构复杂性和阻碍聚合的空间位阻，通过接枝法合成它们极具挑战性。在此，我们报道了通过开环易位聚合合成含酯树枝状结构直至第六代（G6）的聚降冰片烯（PNB）的首个实例。这是通过接枝法制备的树枝状聚合物中聚合的最高代数，得到了分子量高达1960 kg/mol的树枝状高分子。尺寸排阻色谱、光散射和中子散射的结合使得对这些稀溶液中的大型树枝状高分子进行全面的结构研究成为可能。一个半柔性圆柱体模型成功地用于表示静态和动态实验量，得出了持久长度（ ）、横截面半径（ ）和轮廓长度（）。树枝状高分子的持久性似乎随代数增加而增加，对于PNB - G6， 达到27 nm（库恩长度54 nm），表明其呈棒状构象。聚（内 - 三环[4.2.2.0]癸 - 3,9 - 二烯）（PTD）树枝状高分子比同一代的PNB类似物表现出更大的持久性，这可能是由于PTD树枝状高分子的接枝密度更高。由于树枝状侧链将形状各向异性引入树枝状高分子主链，未来的工作将包括对这些体系在浓溶液和熔体中的研究。
