Bottlebrush Block Polymers: Quantitative Theory and Experiments

Samuel J. Dalsin, Thomas G. Rions-Maehren, Marissa D. Beam, Frank S. Bates, Marc A. Hillmyer, Mark W. Matsen

Research output: Contribution to journalArticlepeer-review

80 Scopus citations

Abstract

The self-assembly of bottlebrush block polymers into a lamellar phase was investigated using a combination of experiment and self-consistent field theory (SCFT). Nine diblock bottlebrush polymers were synthesized with atactic polypropylene side chains (block A) and polystyrene side chains (block B) attached to poly(norbornene) backbones of various contour lengths, L, and the resulting lamellar structures were analyzed using small-angle X-ray scattering. The scaling of the lamellar period, d0 ∼ Lγ, exhibited an increasing exponent from γ ≈ 0.3 at small L to γ ≈ 0.9 at large L. The small exponents occurred for starlike molecules where the size of the side chains is comparable to L, while the larger exponents occurred for the more brushlike molecules where the side chains extend radially outward from the backbone. The bottlebrushes were then modeled using flexible side chains of types A and B attached to a semiflexible backbone with an adjustable persistence length, ξb. The resulting SCFT predictions for d0 showed remarkable quantitative agreement with the experimental data, where ξb was similar to the radius of the bottlebrushes. The theory was then used to examine the joint-distribution functions for the position and orientation of different segments along the backbone. This revealed a bilayer arrangement of the bottlebrushes in the lamellar phase, with a high degree of backbone orientation at the A/B interfaces that almost completely vanished near the center of the domains. This finding clearly refutes the prevailing interpretation that the large scaling exponent γ is a result of highly extended backbone conformations.

Original languageEnglish (US)
Pages (from-to)12233-12245
Number of pages13
JournalACS nano
Volume9
Issue number12
DOIs
StatePublished - Nov 6 2015

Bibliographical note

Funding Information:
We acknowledge ExxonMobil Chemical Company for providing vinyl-terminated aPP starting material and financial support for this work. Support from the Center for Sustainable Polymers at the University of Minnesota, a National Science Foundation (NSF)-supported Center for Chemical Innovation (CHE-1413862) is also acknowledged. Portions of the work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by The Dow Chemical Company, E.I. DuPont de Nemours & Co., and Northwestern University. Use of the APS, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract DE-AC02-06CH11357. We also thank Morgan Schulze for her assistance in macromonomer synthesis, and Justin Bolton for helpful discussions regarding bottlebrush polymer synthesis techniques.

Publisher Copyright:
© 2015 American Chemical Society.

Keywords

  • block copolymer
  • bottlebrush
  • lamellae
  • self-assembly
  • self-consistent field theory

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