Amphiphilic Bottlebrush Block Copolymers: Analysis of Aqueous Self-Assembly by Small-Angle Neutron Scattering and Surface Tension Measurements

Mohammed Alaboalirat, Luqing Qi, Kyle J. Arrington, Shuo Qian, Jong K. Keum, Hao Mei, Kenneth C. Littrell, Bobby G. Sumpter, Jan Michael Y. Carrillo, Rafael Verduzco, John B. Matson

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Abstract

A systematic series of 16 amphiphilic bottlebrush block copolymers (BCPs) containing polystyrene and poly(N-acryloylmorpholine) (PACMO) side chains were prepared by a combination of atom-transfer radical polymerization (ATRP), photoiniferter polymerization, and ring-opening metathesis polymerization (ROMP). The grafting-through method used to prepare the polymers enabled a high degree of control over backbone and side-chain molar masses for each block. Surface tension measurements on the self-assembled amphiphilic bottlebrush BCPs in water revealed an ultralow critical micelle concentration (cmc), 1-2 orders of magnitude lower than linear BCP analogues on a molar basis, even for micelles with >90% PACMO content. Combined with coarse-grained molecular dynamics simulations, fitting of small-angle neutron scattering traces (SANS) allowed us to evaluate solution conformations for individual bottlebrush BCPs and micellar nanostructures for self-assembled macromolecules. Bottlebrush BCPs showed an increase in anisotropy with increasing PACMO content in toluene-d8, which is a good solvent for both blocks, reflecting an extended conformation for the PACMO block. SANS traces of bottlebrush BCPs assembled into micelles in D2O, a selective solvent for PACMO, were fitted to a core-shell-shell model, suggesting the presence of a partially hydrated inner shell. Results showed an average micelle diameter of 40 nm with combined shell diameters ranging from 16 to 18 nm. A general trend of increased stability of micelles (i.e., resistance to precipitation) was observed with increases in PACMO content. These results demonstrate the stability of bottlebrush polymer micelles, which self-assemble to form spherical micelles with ultralow (<70 nmol/L) cmc's across a broad range of compositions.

Original languageEnglish
Pages (from-to)465-476
Number of pages12
JournalMacromolecules
Volume52
Issue number2
DOIs
StatePublished - Jan 22 2019

Funding

*E-mail [email protected]. *E-mail [email protected]. ORCID Shuo Qian: 0000-0002-4842-828X Bobby G. Sumpter: 0000-0001-6341-0355 Jan-Michael Y. Carrillo: 0000-0001-8774-697X Rafael Verduzco: 0000-0002-3649-3455 John B. Matson: 0000-0001-7984-5396 Funding This work was supported by Saudi Aramco (fellowship to M.A.), the American Chemical Society Petroleum Research Fund (54884-DNI7), and the National Science Foundation (CMMI-1563008). A portion of this work was supported by the NSF Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (EEC-1449500). Portions of this research were conducted at the Center for Nanophase Materials Sciences (CNMS) and at the CG-2 GP-SANS beamline, High Flux Isotope Reactor (HFIR), which are sponsored at Oak Ridge National Laboratory by the User Facilities Division of the Office of Basic Energy Sciences, U.S. Department of Energy (DOE). The Bio-SANS (CG3) at HFIR is sponsored by the Office of Biological and Environment Research, U.S. DOE. This research also used resources of the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC05-00OR22725. This work benefited from the use of the SasView application, originally developed under NSF Award DMR-0520547. SasView also contains code developed with funding from the EU Horizon 2020 program under the SINE2020 project Grant No. 654000. Notes The authors declare no competing financial interest. This research also used resources of the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC05-00OR22725. This work benefited from the use of the SasView application, originally developed under NSF Award DMR-0520547. SasView also contains code developed with funding from the EU Horizon 2020 program under the SINE2020 project Grant No. 654000.

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