Investigating the Effect of Coronal Charge Patterning on the Solution Structure of Amphiphilic Polypeptoid Multiblock Copolymers

Louisiana State University, Baton Rouge LA

Investigators

Abstract

With this award, the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry is funding Professor Donghui Zhang of the Department of Chemistry at Louisiana State University to investigate the structure of amphiphilic charged block copolymers in aqueous solution. Amphiphilic copolymers are long chain molecules possessing both water-loving and fat-loving segments. Artificial compounds such as soaps and detergents and naturally occurring lipoproteins also have amphiphilic properties. The team studies how the overall charge in these polymers controls the shapes of aggregates formed in solution. Stimuli-responsive behavior of these aggregates is also investigated through control of water acidity or pH. Polymers prepared in this project could have a potential impact in the biomedical area, especially in the field of smart drug delivery. This team provides an interdisciplinary training environment for student researchers. Students who participate in the research program gain experience in polymer synthesis and characterization. Beyond research and mentoring in a laboratory, this project also connects with ongoing outreach efforts. Activities include ChemDemo and You Be the Chemist (YBTC) programs at K-12 schools aimed at increasing the awareness of the importance of polymer chemistry in modern society. This research is focused on understanding the effects of coronal charge patterning (the number and relative position of ionizable monomers on the coronal chains) on the equilibrium aggregate structure of amphiphilic ionic block copolymers (BCPs) in the dilute aqueous solution. This knowledge is attained by judicious design and synthesis of amphiphilic polypeptoid multiblock copolymers (mBCPs) where the coronal charge pattern is controlled by the block length and sequence of ionizable monomers on the coronal chain, and the characterization of their dilute solution structure by a combination of established experimental methods. The central hypothesis is that the local electrostatic interactions encoded in the coronal block sequence of amphiphilic mBCPs influences the equilibrium aggregate structure by modulating the interchain packing, chain conformation, and water distribution in the aggregates. There are three main objectives associated with the project. The first objective focuses on the synthesis of amphiphilic polypeptoid multiblock copolymers having defined block length and sequence of ionizable monomers by sequential controlled ring-opening polymerization methods. In the second objective, the effects of coronal charge pattern on the equilibrium polypeptoid aggregate structures that result from their solution self-assembly in water are systematically investigated. The last objective concentrates on stimuli-responsive behavior of these polypeptoid aggregate solutions, with a strong emphasis on the pH-induced structural transitions. This research could lead to new design rules and reliable protocols in producing polypeptoid-based nanostructures with controlled dimension, geometry, internal structure and pH-responsive characteristics. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.