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

Fabien Dutertre,Ki-Taek Bang,Benoit Loppinet,Tae-Lim Choi,Sanghee Yang,Emmanouil Vereroudakis,Sung-Yun Kang,George Fytas

doi:10.1021/acs.macromol.9b00457

Abstract

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-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.

Highlights

The ability to systematically synthesize macromolecules with well-defined architecture has long been a goal of polymer chemistry as macromolecules with specific functionalities and complex architectures can possess unique properties
We introduced the rigid biphenyl spacer between the active monomer and dendron, which is necessary to reduce the steric hindrance during the propagation, compromising slight loss of chain rigidity.[35,42]
We have reported on the conformation of denpols containing G0 and G3 dendron using static and dynamic light scattering[19] (Table 1, entries 1−5 and 15−16)

Summary

Introduction

The ability to systematically synthesize macromolecules with well-defined architecture has long been a goal of polymer chemistry as macromolecules with specific functionalities and complex architectures can possess unique properties. This is, for example, the case of graft or bottlebrush polymers, a class of branched macromolecules consisting of linear polymers as side chains grafted on the main-chain polymers. They exhibited unique properties with potential applications in the field of photonic crystals,[1] photolithograpy,[2] and biological elastomers.[3] a precise control on the polymer architecture is still elusive due to polydispersity and defects issues of the polymeric side chains. The connection between dendron size (crosssectional radius) and chain rigidity has been rarely investigated.[12,13]

Results

Discussion

Conclusion