Self-Assembly of ABC Bottlebrush Triblock Terpolymers with Evidence for Looped Backbone Conformations

Daniel F. Sunday, Alice B. Chang, Christopher D. Liman, Eliot Gann, Dean M. Delongchamp, Lars Thomsen, Mark W. Matsen, Robert H. Grubbs, Christopher L. Soles

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


Bottlebrush block copolymers offer rich opportunities for the design of complex hierarchical materials. As consequences of the densely grafted molecular architecture, bottlebrush polymers can adopt highly extended backbone conformations and exhibit unique physical properties. A recent report has described the unusual phase behavior of ABC bottlebrush triblock terpolymers bearing grafted poly(dl-lactide) (PLA), polystyrene (PS), and poly(ethylene oxide) (PEO) blocks (LSO). In this work, a combination of resonant soft X-ray reflectivity (RSoXR), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and self-consistent field theory (SCFT) was used to provide insight into the phase behavior of LSO and underlying backbone chain conformations. Consistent with SCFT calculations, RSoXR measurements confirm a unique mesoscopic ACBC domain connectivity and decreasing lamellar periods (d0) with increasing backbone length of the PEO block. RSoXR and NEXAFS demonstrate an additional unusual feature of brush LSO thin films: when the overall film thickness is ∼3.25d0, the film-air interface is majority PS (>80%). Because PS is the midblock, the triblocks must adopt looping configurations at the surface, despite the preference for the backbone to be extended. This result is supported by backbone concentrations calculated through SCFT, which suggest that looping midblocks are present throughout the film. Collectively, this work provides evidence for the flexibility of the bottlebrush backbone and the consequences of low-χ block copolymer design. We propose that PEO blocks localize at the PS/PLA domain interfaces to screen the highest χ contacts in the system, driving the formation of loops. These insights introduce a potential route to overcome the intrinsic penalties to interfacial curvature imposed by the bottlebrush architecture, enabling the design of unique self-assembled materials.

Original languageEnglish (US)
Pages (from-to)7178-7185
Number of pages8
Issue number18
StatePublished - Sep 25 2018

Bibliographical note

Funding Information:
The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract DE-AC02-05CH11231. We thank Eric Gullikson for assistance at BL. 6.3.2. This research was undertaken on the SXR beamline at the Australian Synchrotron, part of ANSTO. This work was supported by the National Science Foundation under Award CHE-1502616. A.B.C. thanks the U.S. Department of Defense for support through the NDSEG Fellowship.

Publisher Copyright:
Copyright © 2018 American Chemical Society.


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