Combs and Bottlebrushes in a Melt

Abstract

We use a combination of the coarse-grained molecular dynamics simulations and scaling analysis to study conformations of bottlebrush and comb-like polymers in a melt. Our analysis shows that a crossover between comb and bottlebrush regimes is controlled by the crowding parameter, Φ, describing overlap between neighboring macromolecules. In comb-like systems characterized by a sparse grafting of side chains (Φ < 1), the side chains and backbones belonging to neighboring macromolecules interpenetrate. However, in bottlebrushes with densely grafted side chains (Φ ≥ 1), the interpenetration between macromolecules is suppressed by steric repulsion between side chains. In this regime, bottlebrush macromolecules can be viewed as filaments with diameter proportional to size of the side chains. For flexible side chains, the crowding parameter is given by Φ ≈ [v/(lb)3/2]­[(n sc/n g + 1)/n sc 1/2], which depends on both the architectural parameters (degree of polymerization of the side chains, n sc, and number of backbone bonds between side chains, n g) and chemical structure of monomers (bond length l, monomer excluded volume v, and Kuhn length, b). Molecular dynamics simulations corroborate this classification of graft polymers and show that the effective macromolecule Kuhn length, b K, and the mean-square end-to-end distance of the backbone, ⟨R e,bb 2⟩, are universal functions of the crowding parameter Φ for all studied systems.

Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties

“…In their recent work, [32] they divided the bottlebrush regime into three different subregions including stretched backbone (SBB), stretched side chain (SSC), and rod-like side chain (RSC) according to the volume fraction of the backbone, φ bb = n g /(n g + n sc ) and n sc . In their recent work, [32] they divided the bottlebrush regime into three different subregions including stretched backbone (SBB), stretched side chain (SSC), and rod-like side chain (RSC) according to the volume fraction of the backbone, φ bb = n g /(n g + n sc ) and n sc .…”

“…In the current paper, we investigate the transitions from comb to bottlebrush behavior; therefore, all of these variables are used for both topologies especially in the transition from comb to bottlebrush conformations. Substantial experimental [11,[29][30][31] and coarse-grained simulation works along with scaling analysis [24,25,[32][33][34][35] have been done to classify graft polymers into comb and bottlebrush classes with distinct rheological and mechanical properties. Substantial experimental [11,[29][30][31] and coarse-grained simulation works along with scaling analysis [24,25,[32][33][34][35] have been done to classify graft polymers into comb and bottlebrush classes with distinct rheological and mechanical properties.…”

“…The differences observed between comb and bottlebrush structures were related to the Gaussian and stretched conformations of the backbone and side chains. [3,24,25,32,44] Side chains in comb polymers increase the friction of the backbone chain with neighboring molecules in the melt or solution state, which enhances the strain hardening (see below) of the polymer melt under processing conditions. The side chains of the comb topologies can easily overlap physically with each other, while densely grafted bottlebrush molecules are segregated and weakly penetrated.…”

“…Substantial experimental [11,[29][30][31] and coarse-grained simulation works along with scaling analysis [24,25,[32][33][34][35] have been done to classify graft polymers into comb and bottlebrush classes with distinct rheological and mechanical properties. The differences observed between comb and bottlebrush structures were related to the Gaussian and stretched conformations of the backbone and side chains.…”

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

“…The grafting density and distribution of grafts along the backbone determine the steric interactions between side chains and in turn influence the physical properties. Graft polymers display many unique properties compared to their linear analogues, such as extended chain conformations, [5][6][7][8] increased entanglement molecular weights, [9][10][11][12] and architecturedependent rheological behavior. [13][14][15][16] Recent studies have harnessed these properties in a wide variety of applications in photonics, [17][18][19] drug delivery, [20][21][22] transport, [23][24] and thermoplastics.…”