Conformation of Tunable Nanocylinders: Up to Sixth-GenerationDendronized Polymers via Graft-Through Approach by ROMP

摘要

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 (lp), cross-sectional radius (Rcs), and contour length (L). The denpol persistency seemed to increase with generation, with lp reaching 27 nm (Kuhn length 54 nm) for PNB-G6, demonstrating a rod-likeconformation. Poly(endo-tricycle[4.2.2.0]deca-3,9-diene) (PTD) denpolsexhibited larger persistency than the PNB analogues of the same generationpresumably due to the higher grafting density of the PTD denpols.As the dendritic side chains introduce shape anisotropy into the denpolbackbone, future work will entail a study of these systems in theconcentrated solutions and melts.