Molecular Bottle Brushes with Positioned Selenols: Extending the Toolbox of Oxidative Single Polymer Chain Folding with Conformation Analysis by Atomic Force Microscopy

Emmanuelle Schué,Hans G Börner,Alexey Kopyshev,Jean‐François Lutz

doi:10.1002/pola.29496

Abstract

ABSTRACTA synthesis route to controlled and dynamic single polymer chain folding is reported. Sequence‐controlled macromolecules containing precisely located selenol moieties within a polymer chain are synthesized. Oxidation of selenol functionalities lead to diselenide bridges and induces controlled intramolecular crosslinking to generate single chain collapse. The cyclization process is successfully characterized by SEC as well as by 1H NMR and 2D HSQC NMR spectroscopies. In order to gain insight on the molecular level to reveal the degree of structural control, the folded polymers are transformed into folded molecular brushes that are known to be visualizable as single molecule structures by AFM. The “grafting onto” approach is performed by using triazolinedione−diene reaction to graft the side chain polymers. A series of folded molecular brushes as well as the corresponding linear controls are synthesized. AFM visualization is proving the cyclization of the folded backbone by showing globular objects, where non‐folded brushes show typical worm‐like structures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 154–162

Highlights

Sequence Controlled Polymerization Controlled radical copolymerization of electron-rich styrene derivatives with a sub-stoichiometric amount of N-substituted maleimides allows the synthesis of copolymers with wellcontrolled molecular weight distribution and positioned insertions of maleimides along the polymer chain.57 4-tertbutoxystyrene (S-OtBu) was selected as styrene-based monomer, bearing a protected functionality that will later allow to introduce polymer side chains at each repeating unit to generate the molecular brush structure [Scheme 1 and Fig. 5]
The Mal-SeMob synthesis was adapted from recent literature protocols.[58,59,60]
The observation of globular objects could potentially suggest the presence of a folded backbone structure, where the full extension of the brush backbone is prevented due to intramolecular diselenide bridges that lock the backbone into a cyclic topology

Summary

Introduction

The information rich biomacromolecules such as peptide/proteins, nucleotides/RNA/DNA, and saccharides have been source of inspiration for polymer sciences throughout decades.[1,2] Intense research was dedicated to mimic features of biopolymer classes with synthetic macromolecules.[3,4,5] designing polymers that can fold into structures with the precision, the complexity, and the variability of biomacromolecules is still demanding.[6,7,8,9,10]The introduction of living/controlled polymerizations, including methods of controlled radical polymerization (CRP)[11] paved the way to access complex, multifunctional polymer architectures.[12,13,14,15,16,17,18] Routes to different topologies such as cyclic or multi-cyclic polymers were developed, by combining CRP with chain-end functionalization to induce intramolecular crosslinking.[19,20] More recently, block and statistical copolymers have been exploited to insert intramolecular bridges and thereby inducing single chain folding.[21,22,23,24,25] Covalent, dynamic covalent, and supramolecular bonds were used to generate static or dynamic single chain folding.[26,27,28] Elegant supramolecular single polymer chain compactions based on single or combination of orthogonal hydrogen-bonding tectons have been thoroughly reported.[29,30,31]. The styrene/maleimide copolymerization enabled the positioning of functional monomer units in growing polymer chains and controlled intramolecular crosslinking by click chemistry have been investigated.[46]

Results

Conclusion