Brush-Like Polymers and Entanglements: From Linear Chains to Filaments

Journal Article · Thu Sep 26 00:00:00 EDT 2019 · ACS Macro Letters

DOI:https://doi.org/10.1021/acsmacrolett.9b00519· OSTI ID:1574445

Liang, Heyi ^[1]; Grest, Gary S. ^[2]; Dobrynin, Andrey V. ^[1]

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1. Univ. of Akron, OH (United States)
2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Dynamics of melts and solutions of high molecular weight polymers and biopolymers is controlled by topological constraints (entanglements) imposing a sliding chain motion along an effective confining tube. For linear chains, the tube size is determined by universal packing number P_e, the number of polymer strands within a confining tube that is required for chains to entangle. In this work, we show that in melts of brush-like (graft) polymers, consisting of linear chain backbones with grafted side chains, P_e is not a universal number and depends on the molecular architecture. Specifically, we use coarse-grained molecular dynamics simulations to demonstrate that the packing number is a nonmonotonic function of the ratio R_nsc/R_ng of the size of the side chains R_nsc to that of the backbone spacer between neighboring grafting points R_ng. This parameter characterizes the degree of mutual interpenetration between side chains of the same macromolecule. We demonstrate that P_e of brush-like polymers first decreases with increasing side chain grafting density in the dilute side chain regime (R_nsc < R_ng), then begins to increase in the regime of overlapping side chains (R_nsc > R_ng), approaching the value for linear chains in the limit of densely grafted side chains. This dependence of the packing number reflects a crossover from chain-like entanglements in systems with loosely grafted side chains (comb-like polymers) to entanglements between flexible filaments (bottlebrush-like polymers). Our simulation results are in agreement with the experimental data for the dependence of a plateau modulus on the molecular architecture of graft poly(n-butyl acrylates) and poly(norbornene)-graft-poly(lactide) melts.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000; NA0003525
• OSTI ID: 1574445
• Report Number(s): SAND--2019-12126J; 680158
• Journal Information: ACS Macro Letters, Journal Name: ACS Macro Letters Journal Issue: 10 Vol. 8; ISSN 2161-1653
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE