Cyclic vs Linear Bottlebrush Polymers in Solution: Side-Chain Length Effect

Abstract

Bottlebrush polymers (BBPs) of different architecture are of considerable interest for a broad range of applications, including nanomedicine, electronics, and self-healing materials. Using atomistic molecular dynamics simulations, we investigate and compare the structural and hydration properties of cyclic and linear poly(vinyl alcohol)-graft-poly(ethylene oxide) (PVA-g-PEO N sc ) BBPs in aqueous solution as functions of PEO side-chain length, N sc. We find that overall cyclic BBPs are smaller than the corresponding linear BBPs and their shape changes from donutlike to disklike to starlike with increasing side-chain length, while linear BBPs vary in shape from an expanded coil to a rod/cylinder. The radius of gyration of cyclic BBPs increases with an increase of the side-chain length at a somewhat slower rate than the linear BBPs but follows the same scaling R g ∼ N sc 0.58 in the limit of long side chains. For short grafts, we determine that the persistence length, l p, for both cyclic and linear BBPs increases in a similar manner following an l p ∼ N sc 0.54 dependence. In the long side-chain limit, the persistence length (l p) of cyclic BBP saturates, while for linear BBPs l p strongly increases following the expected scaling relation l p ∼ N sc 15/8. We propose a scaling model that shows that the fraction of side-chains located inside the cyclic BBPs depends on the radius of the backbone ring and significantly decreases with an increase of graft length. For both cyclic and linear BBPs, the hydrogen bonding between PEO side chains and water is somewhat reduced near the backbone, where local chain stretching is observed, while reaching full hydration on the periphery. Overall, the hydration shell within 1 nm of the cyclic BBP backbone is found to be more dynamically stable compared to linear BBPs.

All-Atom Molecular Dynamics Simulations of Uncharged Linear Polymer Bottlebrushes: Effect of the Brush Sizes and the Number of Side-Chain Monomers

“…This is evidenced by larger values of κ 2 and stems from the fact that the side chains contribute very little to the overall shape of the BBP. Such dependences of the κ 2 of the BBPs on relative values of the sizes of backbone and the side chains of the BBPs qualitatively match with the results published in previous studies . On the other hand, for same N BB values, but larger N SC values ( N SC = 10, 15, 20, 25), the presence of the side chains significantly contributes to the overall shape of the BBPs, ensuring a more sphere-like configuration, evidenced by a much smaller value of κ 2 .…”

“…A significant limitation of such CG MD simulations is that they fail to provide (1) explicit description of the manner in which individual atoms of the backbone or the side chain of the BBPs dictate the overall BBP structure and (2) the effect of the BBPs on detailed water structure, such as hydration, hydrogen bonding, water dipole distribution, and water structural order. In a recent major effort, Chen and Dormidontova employed all-atom MD simulations for studying the BBPs and in the process addressed some of these limitations. Specifically, they investigated the linear and cyclic BBPs and identified unique water structures around the BBPs.…”

polyGraft 1.0: A program for molecular structure and topology generation of polymer‐grafted hybrid nanostructures

“…For example, the backbone gains rigidity upon side chain length increase 23 and the induced steric effect significantly reduces the possibility to form molecular entanglements 25 compared to conventional linear polymers. In addition, the backbone topology and side chain length affect the structural and hydration properties, revealed by atomic MD simulations using the structure and topology generated by polyGraft 50 . Apart from the backbone topology and chain length of backbones and grafts, the grafting density is also an important parameter determining the structural properties of bottlebrush polymers.…”

Worm-globule transition of amphiphilic pH-responsive heterografted bottlebrushes at air–water interface

“…When the aspect ratio, that is, N BB /N SC , where N BB is the degree of polymerization (DP) of the backbone and N SC is the DP of side chains, is sufficiently high, MBBs exhibit cylindrical conformations, 1–6 resembling bottlebrush flowers and brushes for bottles and pipes. Brush polymers have attracted considerable interest in recent years, from synthesis to study of structures and assemblies; 7–22 many unique characteristics have been revealed, such as large and tunable persistence length, no backbone entanglements, and unusual crystal habits. 1–25 A variety of potential applications of MBBs have been demonstrated, ranging from photonic crystals to drug delivery systems, lubricants, and emulsion stabilizers.…”

“…Brush polymers have attracted considerable interest in recent years, from synthesis to study of structures and assemblies; 7–22 many unique characteristics have been revealed, such as large and tunable persistence length, no backbone entanglements, and unusual crystal habits. 1–25 A variety of potential applications of MBBs have been demonstrated, ranging from photonic crystals to drug delivery systems, lubricants, and emulsion stabilizers. 26–37…”