Design, Structure, and Properties of Polymeric Materials with Programmed Macromolecular Architectures

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

PART 1: NON-TECHNICAL SUMMARY This research program will draw inspiration from a combination of fundamental principles derived from the metallurgy of metal alloy phases and some of the most fundamental principles of biology such as homochirality, and apply them to the design and synthesis of individual macromolecules with simple and complex architectures that may include memory effects, which will allow to discover new concepts in complex polymeric materials. These concepts are anticipated to be competitive with the most efficient methodologies currently available in biology. The outcome of this work is expected to facilitate control of supramolecular electronic properties of interest for applications such as solar cells, new tools for medical devices including drug delivery, environmental aspects of polymer materials, and other uses. This research involves an interdisciplinary program at the interface between organic, macromolecular and supramolecular chemistry, physics, biology, synthetic biology, and materials science; it also includes collaborations with scientists from around the world. This program will also enable the education of undergraduate and graduate students, high-school students, and postdoctoral scientists. PART 2: TECHNICAL SUMMARY The Frank-Kasper phases were first discovered and employed in metal alloys. In soft matter they were discovered in a related NSF program and recently also in block-copolymers, surfactants and other assemblies. They are expected to evolve soon into new technological applications. However, many supramolecular spherical assemblies are helical and therefore chiral and the molecular mechanism as well as the role of homochirality in these phases remains to be understood. The structures and properties generated by memory effects in these materials are accessible only by chiral supramolecular dendrimers and by other monodisperse assemblies. Therefore, this project will elucidate the role of chirality in Frank-Kasper soft phases and will be fundamental for the development of new material properties from polymers and any other organic materials. Even though most polymeric and organic materials exhibit helical structures and are therefore chiral, they are considered to be racemic when assembled from achiral or racemic building blocks and display low-ordered structures and properties. This supramolecular trend is similar to that of isotactic (homochiral), syndiotactic (heterochiral), and atactic (racemic) polymers. A new mechanism of crystallization, the cogwheel mechanism that disregards chirality, has recently been discovered and shown to be potentially able to eliminate the difference regarding the perfection of helical structures generated from chiral versus racemic building blocks. The generality of this mechanism to combinations of racemic and achiral building blocks to generate the same material properties as the homochiral ones will be studied. The outcome of this research will have broad scientific impact across many types of materials, including electronic, medical, and other applications. Another aspect of this project involves monodisperse polymers. Monodisperse polymers containing single-dimension species are produced only by biology. This research will include continued development of self-interrupted living polymerization, which will enable study of similarities and differences between the structure and properties of truly monodisperse polymers versus those of narrow dispersity produced by standard living polymerizations. These will also impact broad areas involving the design of polymeric materials with numerous potential applications. 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.