Exchange Kinetics for a Single Block Copolymer in Micelles of Two Different Sizes

Dan Zhao, Yuanchi Ma, Timothy P. Lodge

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

The effect of micellar size on the chain exchange kinetics in spherical micelles consisting of poly(methyl methacrylate)-block-poly(n-butyl methacrylate) (PMMA-b-PnBMA) in a mixture of ionic liquids (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI], and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [BMIM][TFSI]) was investigated using time-resolved small-angle neutron scattering (TR-SANS). Two spherical micelles with different core sizes were prepared from a single block copolymer by using different protocols. In one case the micelles were formed in the presence of a cosolvent, while in the other a polymer thin film was directly dissolved in the ionic liquid. Interestingly, the micelle core size prepared from the latter method is ∼30% larger than that obtained in the former case. TR-SANS experiments reveal that the rate of single chain exchange in the micelles with a larger core size is slowed down by ∼3 times compared to the smaller core radius. This can be possibly attributed to the smaller interfacial area per chain, and larger corona density, for micelles with a larger core dimension. These geometrical factors can potentially lead to changes in both the attempt time and activation barrier for chain expulsion during the unimer exchange process. Our results clearly suggest that, in addition to the molecular characteristics of the block copolymer and solvent, the geometrical structure of the micelle plays an important role in the unimer dynamic exchange processes in block copolymer micelles.

Original languageEnglish (US)
Pages (from-to)2312-2320
Number of pages9
JournalMacromolecules
Volume51
Issue number6
DOIs
StatePublished - Mar 27 2018

Bibliographical note

Funding Information:
The authors acknowledge financial support from National Science Foundation (DMR-1707578). Portions of this 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 Northwestern University, E.I. DuPont de Nemours & Co., and The Dow Chemical Company. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. We acknowledge the support of the National Institute of Standards and Technology (NIST), U.S. Department of Commerce, in providing the neutron research facilities used in this work. We thank Dr. Yimin Mao and Dr. Paul Butler for their assistance in SANS measurements. The NIST Center for Neutron Research is also acknowledged for providing access to the DynaPro NanoStar instrument. We thank Frank Bates, En Wang, and David Morse for helpful discussions.

Funding Information:
The authors acknowledge financial support from National Science Foundation (DMR-1707578). Portions of this 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 Northwestern University, E.I. DuPont de Nemours & Co., and The Dow Chemical Company. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. We acknowledge the support of the National Institute of Standards and Technology (NIST), U.S. Department of Commerce, in providing the neutron research facilities used in this work. We thank Dr. Yimin Mao and Dr. Paul Butler for their assistance in SANS measurements. The NIST Center for Neutron Research is also acknowledged for providing access to the DynaPro NanoStar instrument. We thank Frank Bates, En Wang, and David Morse for helpful discussions.

Publisher Copyright:
© 2018 American Chemical Society.

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