The properties and performance of many biological materials rely on the structures and shapes of their constituent molecules, which could be in the form of helices or sheets. Some of the protein materials are even made from predominantly one type of such structure, showing that high material performance can be achieved by relatively simple structural motifs. This project aims to elucidate how a class of synthetic polymers, which possess both a relatively complex molecular architecture and well-defined secondary structural motifs, may allow for the development of new materials with predictable physical properties. The different ways of intermolecular and intramolecular interactions in these complex polymer molecules may turn out to be the primary factor that determines the macroscopic properties. Successful completion of this research may enable the generation of polymeric systems that will approach the level of sophistication and versatility found in some of nature's biomaterials and the properties of these materials may be tailored for a variety of applications. This research project entails the design and preparation of such complex molecules and their supramolecular assemblies, as well as the study of their properties. It also provides a model system of complex macromolecules, enabling comparison of the multiscale assembly and the material properties with predictions from computer simulations and modeling. Graduate and undergraduate students will be trained in this area and acquire skills in polymer synthesis, material characterization, and computer simulations. The program will integrate the research with the development of interdisciplinary courses on bioinspired polymeric materials, provide vibrant research experiences to undergraduates and high-school students, and promote polymer research and its impact on society through lectures and workshops for the public. Emphasis is given to involving underrepresented students at all levels.
Using living polymerizations and other strategies, polymers with complex architectures and controlled molecular structures can be synthesized for new materials. One central question that arises is how to control the organization of these complex polymers at different scales to achieve targeted material properties. This research puts a particular emphasis on the secondary structures of complex synthetic polymers, and the connection between the different organizations of the structural motifs and the performance of resulting materials. The model system used in this research is the comb-like macromolecules containing polyamino acids (PAAs) as the side chains. Synthetic PAAs are polypeptide model systems that can form alpha-helix or beta-sheet structures, and that can be made on a large scale. Current studies mainly focus on the linear PAAs and their various copolymers. However, incorporating PAAs into complex macromolecular architectures (e.g., comb-like or brush-like) has profound effects on the association and physical properties of the polymers. The research aims to elucidate the relationship between the structural configuration and the material properties of the PAA-grafted comb macromolecules. The investigation begins with the use of water-soluble PAAs that form intermolecular beta-sheets, to guide the association of the comb macromolecules into fibril-based thin films. The mechanical properties of the polymer films will be compared with those made from proteins or linear PAAs. The study will then continue on the hydrophobic PAAs that form alpha-helices, and determine how different structural configurations of the helices may dictate the morphology and mechanical properties of the PAA-grafted comb macromolecules. At the end of the project, the stress-induced transformation of alpha-helix to beta-sheet in the PAA-grafted comb macromolecules will be examined.
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.
