(6hv) Functional Polymers for Molecular and Materials Design

Molecular shape impacts the self-assembly and physical properties of all soft materials. In polymer science and engineering, shape control can be achieved by tuning the polymer architecture, local non-covalent interactions, and/or responses to external stimuli. My research program will connect polymer chemistry and polymer physics in order to explore the impact of molecular shape in different contexts across molecular and materials design. We will use creative chemistry in order to address challenges in polymer physics, and in turn bring insights from polymer physics to enable new reactivity.

Research Experience:

Graduate Student, Department of Chemistry, California Institute of Technology, Prof. Robert H. Grubbs

Synthesis and Self-Assembly of Bottlebrush Polymers. Bottlebrush polymers represent a unique molecular architecture and a modular platform for materials design. However, the properties and self-assembly of bottlebrush polymers remain relatively unexplored, in large part due to synthetic challenges imposed by the sterically demanding architecture. My graduate research aimed to close these gaps, connecting (1) the synthesis of polymers with precisely tailored molecular architectures, (2) the study of fundamental structure-property relationships, and (3) the design of functional materials. I developed a versatile strategy to synthesize polymers with tailored architectures via grafting-through ring-opening metathesis polymerization (ROMP). One-pot copolymerization of a macromonomer and a small-molecule co-monomer provides opportunities to control the backbone sequence and therefore both the spacing and distribution of side chains. Homo- and copolymerization rate trends were identified and elucidated by complementary mechanistic and density functional theory (DFT) studies. Building on this foundation, I prepared complex molecular architectures and explored the physical consequences of varying the grafting density and graft distribution in two contexts: block polymer self-assembly and linear rheological properties. The molecular architecture strongly influences packing demands and therefore polymer conformation. Collectively, our studies represent progress toward a universal model connecting the chemistry and conformations of graft polymers.

Beckman Postdoctoral Fellow, Department of Chemical Engineering and Materials Science, University of Minnesota, Twin Cities; Prof. Frank S. Bates

Tough and Sustainable Plastics via Graft Block Polymer Design. The molecular architecture – that is, the way in which polymer chains are connected – dramatically impacts the properties of plastics. My postdoctoral research has focused on developing a modular platform for tough and sustainable plastics based on graft block polymers. Linking two or more chemically distinct blocks structures plastics at the nanoscale, improving the mechanical properties; introducing grafts amplifies shear thinning and strain hardening behavior, improving the melt processability. Precise synthetic control over the graft block architecture enables systematic studies of key structure-property relationships. Understanding design rules based on the molecular architecture — independent of specific choices of block and backbone functionality — allows the materials to both meet the needs of sustainability and be customized for specific applications.

Teaching Interests:

I am prepared and excited to teach a range of subjects, including thermodynamics, chemical kinetics, soft matter physics, and polymer science and engineering. My graduate training in chemistry, together with my postdoctoral experience in a chemical engineering department, provide competency in core areas of chemical engineering as well as perspective on communicating with students with different backgrounds and interests. Beyond the classroom, I am excited to engage in science outreach and research with broader impacts. Students and postdoctoral researchers in my group will benefit from interdisciplinary training in polymer science and engineering, spanning chemistry, physics, and materials design.

Selected Peer-Reviewed Publications:

(* denotes corresponding author; ⁺ denotes equal contributions)

1. Qian, Z.; Koh, Y. P.; Pallaka, M. R.; Chang, A. B.; Lin, T.-P.; Guzmán, P. E.; Grubbs, R. H.; Simon, S. L.; McKenna, G. B. Linear Rheology of a Series of Second-Generation Dendronized Wedge Polymers. Macromolecules 2019, 52, 2063.
2. Sunday, D. F.;* Chang, A. B.;* Liman, C. D.; Gann, E.; DeLongchamp, D. M.; Matsen, M. W.; Grubbs, R. H.; Soles, C. L. Evidence for Backbone Flexibility of Bottlebrush Block Copolymers Driven by Low-χ Assembly. Macromolecules 2018, 51, 7187. (*Corresponding authors.)
3. Haugan, I. N.; Maher, M. J.; Chang, A. B.; Lin, T.-P.; Grubbs, R. H.; Hillmyer, M. A.; Bates, F. S. Consequences of Grafting Density on the Linear Viscoelastic Behavior of Graft Polymers. ACS Macro Lett. 2018, 7, 525.
4. Chang, A. B.;⁺ Lin, T.-P.;⁺ Thompson, N. B.; Luo, S.-X.; Liberman-Martin, A. L.; Chen, H.-Y.; Lee, B.; Grubbs, R. H. Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions. J. Am. Chem. Soc. 2017, 139, 17683.
5. Lin, T.-P.;⁺Chang, A. B.;⁺ Luo, S.-X.; Chen, H.-Y.; Lee, B.; Grubbs, R. H. Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush. ACS Nano 2017, 11, 11632.
6. Chang, A. B.; Bates, C. M.; Lee, B.; Garland, C. M.; Jones, S. C.; Spencer, R. K. W.; Matsen, M. W.; Grubbs, R. H. Manipulating the ABCs of Self-Assembly via Low-χ Block Polymer Design. Proc. Natl. Acad. Sci. 2017, 114, 6462.
7. Lin, T.-P.; Chang, A. B.; Chen, H.-Y.; Liberman-Martin, A. L.; Bates, C. M.; Voegtle, M. J.; Bauer, C. A.; Grubbs, R. H. Control of Grafting Density and Distribution in Graft Polymers by Living Ring-Opening Metathesis Copolymerization. J. Am. Chem. Soc. 2017, 139, 3896.
8. McNicholas, B. J.; Blakemore, J. D.; Chang, A. B.; Bates, C. M.; Kramer, W. W.; Grubbs, R. H; Gray, H. B. Electrocatalysis of CO2 Reduction in Brush Polymer Ion Gels. J. Am. Chem. Soc. 2016, 138, 11160.
9. Bates, C. M.; Chang, A. B.; Schulze, M. W.; Momčilović, N.; Jones, S. C.; Grubbs, R. H. Brush Polymer Ion Gels. J. Polym. Sci., Part B 2016, 54, 292.
10. Bates, C. M.; Chang, A. B.; Momčilović, N.; Jones. S. C.; Grubbs, R. H. ABA Triblock Brush Polymers: Synthesis, Self-Assembly, Conductivity, and Rheological Properties. Macromolecules 2015, 48, 4967.
11. Chang, A. B.; Miyake, G. M.; Grubbs, R. H. Sequence-Controlled Polymers by Ruthenium-Mediated Ring-Opening Metathesis Polymerization. In Sequence-Controlled Polymers: Synthesis, Self-Assembly, and Properties; Ouchi, M., Meyer, T., Lutz, J.-F., Eds.; ACS Symposium Series 1170; American Chemical Society: Washington, DC, 2014; pp 161.

Patents:

1. Grubbs, R. H.; Lin, T.-P.; Chang, A. B.; Chen, H.-Y.; Bates, C. M. Control of Polymer Architectures by Living Ring-Opening Metathesis Copolymerization. U.S. Patent Appl. 15/914,762. March 7, 2018.
2. Grubbs, R. H.; Bates, C. M.; Chang, A. B.; McNicholas, B. J.; Jones, S. C. Brush Block Copolymer Electrolytes and Electrocatalyst Compositions. U.S. Patent Appl. 15/065,317. March 9, 2016.
3. Grubbs, R. H.; Bates, C. M.; Chang, A. B.; McNicholas, B. J.; Jones, S. C. Triblock Brush Block Copolymers. U.S. Patent Appl. 15/065,291. March 9, 2016.

Selected Awards:

• Arnold O. Beckman Postdoctoral Fellowship (2019–Present)
• McCoy Award, California Institute of Technology (2018)
• Gray-Hill Lecturer, Occidental College (2018)
• SciFinder Future Leaders Award (2017)
• American Chemical Society Excellence in Graduate Polymer Research Award (2016)
• American Chemical Society Women Chemists Committee / Merck Research Award (2016)
• National Defense Science and Engineering Graduate Fellowship (2014–2017)
• Phi Beta Kappa, Columbia University (2013)
• Rabi Science Fellowship, Columbia University (2009–2013)

Selected Successful Proposals:

• Arnold O. Beckman Postdoctoral Fellowship (2019–Present)
• National Defense Science and Engineering Graduate Fellowship (2014–2017)
• Advanced Photon Source at Argonne National Laboratory: GUP-43955 (240 hours of beamtime) (2015–2017)
• Advanced Photon Source at Argonne National Laboratory: GUP-55715 (200 hours of beamtime) (2017–2019)