Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

Alice B. Chang, Tzu Pin Lin, Niklas B. Thompson, Shao Xiong Luo, Allegra L. Liberman-Martin, Hsiang Yun Chen, Byeongdu Lee, Robert H. Grubbs

Research output: Contribution to journalArticlepeer-review

60 Scopus citations

Abstract

Grafting density and graft distribution impact the chain dimensions and physical properties of polymers. However, achieving precise control over these structural parameters presents long-standing synthetic challenges. In this report, we introduce a versatile strategy to synthesize polymers with tailored architectures via grafting-through ring-opening metathesis polymerization (ROMP). One-pot copolymerization of an ω-norbornenyl macromonomer and a discrete norbornenyl comonomer (diluent) provides opportunities to control the backbone sequence and therefore the side chain distribution. Toward sequence control, the homopolymerization kinetics of 23 diluents were studied, representing diverse variations in the stereochemistry, anchor groups, and substituents. These modifications tuned the homopolymerization rate constants over 2 orders of magnitude (0.36 M-1 s-1 < khomo < 82 M-1 s-1). Rate trends were identified and elucidated by complementary mechanistic and density functional theory (DFT) studies. Building on this foundation, complex architectures were achieved through copolymerizations of selected diluents with a poly(d,l-lactide) (PLA), polydimethylsiloxane (PDMS), or polystyrene (PS) macromonomer. The cross-propagation rate constants were obtained by nonlinear least-squares fitting of the instantaneous comonomer concentrations according to the Mayo-Lewis terminal model. In-depth kinetic analyses indicate a wide range of accessible macromonomer/diluent reactivity ratios (0.08 < r1/r2 < 20), corresponding to blocky, gradient, or random backbone sequences. We further demonstrated the versatility of this copolymerization approach by synthesizing AB graft diblock polymers with tapered, uniform, and inverse-tapered molecular "shapes." Small-angle X-ray scattering analysis of the self-assembled structures illustrates effects of the graft distribution on the domain spacing and backbone conformation. Collectively, the insights provided herein into the ROMP mechanism, monomer design, and homo- and copolymerization rate trends offer a general strategy for the design and synthesis of graft polymers with arbitrary architectures. Controlled copolymerization therefore expands the parameter space for molecular and materials design.

Original languageEnglish (US)
Pages (from-to)17683-17693
Number of pages11
JournalJournal of the American Chemical Society
Volume139
Issue number48
DOIs
StatePublished - Dec 6 2017

Bibliographical note

Funding Information:
This work was supported by the Department of Energy under Award Number DE-AR0000683 (ARPA-E Program) and by the National Science Foundation under Award Number CHE- 1502616. A.B.C. thanks the U.S. Department of Defense for support through the NDSEG Fellowship. A.L.L.-M. thanks the Resnick Sustainability Institute at Caltech for fellowship support. The authors thank Prof. J. C. Peters for access to computational resources. This research used resources of the Advanced Photon Source, a U.S. Department of Energy Office of Science User Facility operated by Argonne National Laboratory under Contract DE-AC02-06CH11357.

Funding Information:
This work was supported by the Department of Energy under Award Number DE-AR0000683 (ARPA-E Program) and by the National Science Foundation under Award Number CHE-1502616. A.B.C. thanks the U.S. Department of Defense for support through the NDSEG Fellowship. A.L.L.-M. thanks the Resnick Sustainability Institute at Caltech for fellowship support. The authors thank Prof. J. C. Peters for access to computational resources. This research used resources of the Advanced Photon Source, a U.S. Department of Energy Office of Science User Facility operated by Argonne National Laboratory under Contract DE-AC02-06CH11357.

Publisher Copyright:
© 2017 American Chemical Society.

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