CAREER: Block Copolymer Nanoactuators from Liquid Crystalline and Ionomeric Units

University Of Connecticut, Storrs CT

Investigators

Abstract

TECHNICAL SUMMARY An integrated and comprehensive study of new triblock copolymers comprising cholesteric liquid crystalline units in the central block and ionic imidazolium or pyridinium groups in the end blocks for shape-memory applications is the main goal of this proposal. Synthetic methods to prepare monomers bearing cholesteric units, B, and monomers bearing imidazole or pyridine units, A, are described. Steroidal molecules that will be used as side-chain mesogens are chosen for their functionality and their cholesteric LC property. Sequential monomer addition in the order of A, B, and A, by controlled polymerization methods, will be used to prepare ABA triblock copolymers. Due to incompatibility between the different blocks, through a bottom-up approach, a phase-segregated morphology will result from the melts of these ABA triblock copolymers. Cholesteric units are confined to a nanodomain and the cholesteric mesogens are known to arrange in a helical fashion; imidazole or pyridine groups will phase-segregate into separate nanodomains. Triblock copolymer, ABA, will be converted to the ionic form, A'BA'. With the support of this CAREER award, the Kasi group will (1) perform thermal, optical, and morphological analysis of these polymers, (2) investigate the shape-memory behavior of ABA and A'BA' triblock copolymers, (3) establish the influence of confined cholesteric helices on shape-memory behavior of these triblock copolymers and (4) establish the effect of thermal actuation of cholesteric helices which will result in pitch change of helices allowing the design of thermo-responsive selective light reflection media. NON-TECHNICAL SUMMARY Shape-memory polymers exhibit reversible shape changes in the presence of stimulus such as thermal energy. These polymers are used in biomedical applications such as degradable sutures and implants. A step forward is the design and structure-property study of new nanostructured liquid crystalline block copolymers that show a dual-response of shape and light reflection with temperature, which is the primary goal of this CAREER research plan. These new responsive liquid crystalline polymers will find applications in medical devices, smart textiles that change shape and color, and display technologies. The educational and outreach activities that have been initiated by the principal investigator (PI) will link different educational levels by using polymer based research training as an educational tool. Graduate, undergraduate, and high school students working in the PI's group at the University of Connecticut will gain experience in the cross-disciplinary field of responsive polymers. Additionally, the PI has initiated two different science outreach programs targeted towards middle- and high school students from a federally designated high-need district in Connecticut. The goal of the middle-school outreach program is to link science syllabus with innovations in science and technology of ubiquitous materials like polymers through hands-on experimentation. The high school outreach program is a collaborative summer workshop established by the PI and five Chemistry faculty members. The goal of this program is to provide talented under-represented high school students research experience in five sub-fields of chemistry. Introducing these students to exciting research and innovations in chemistry could be a viable method to keep them interested in sciences.