Michael C. Biewer - US grants

The Macromolecular, Supramolecular and Nanochemistry Program in the NSF Division of Chemistry supports Professors Mihaela C. Stefan and Michael C. Biewer of the University of Texas at Dallas to develop biodegradable and biocompatible polymers. The polymers of interest contain both water-friendly (hydrophilic) and water repellent (hydrophobic) segments can assemble in water to form core-shell structures in which the water-insoluble molecules can be loaded. The most attractive property of these polymers is their degradation in water media making them environmentally friendly materials. The project provides training to graduate and undergraduate students in the synthesis and characterization of organic compounds and polymers. High school students are given the opportunity to contribute in a summer research project to learn skills in a chemistry laboratory environment.

The objective of this proposed research is to develop polycaprolactone amphiphilic block copolymers that are biodegradable, biocompatible, and thermoresponsive. The research team aims to control the thermoresponsivity of the amphiphilic block copolymers by varying the ratio between the hydrophilic oligoethylene glycol substituted polycaprolactone hydrophilic block and the hydrophobic polycaprolactone block. To understand the dependence of the degradation rate on the structure of the block copolymers and their composition, the team investigates the effects of changing the linkage of the substituent on the monomers from ether to thioether, and from ester to thioester, on the polymer degradation rate. In addition, investigation of the self-assembly of the synthesized amphiphlic polycaprolactone block copolymers is conducted to obtain a correlation between the molecular structure and the size of micelles.

With the support of the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Michael C. Biewer of the University of Texas at Dallas is developing a photochromic unit based on aromatic molecules that contain nitrogen. The synthesized unit will be attached as a pendant group to a semiconducting organic material, which will subsequently be extended into a conjugated donor-acceptor-donor small molecule. Semiconducting materials are to be constructed based on sulfur-containing conjugated aromatic systems known as thiophenes. Supramolecular stacking of the prepared organic molecules is expected to lead to materials that can become conductive when external voltage is applied (transistor-like behavior) or light shines on them (photovoltaic cell-like behavior). A variety of synthetic manipulations will be performed in order to systematically investigate and maximize the changes in optoelectronic properties upon irradiation with light. This research has the potential to generate novel light-activated and stimuli responsive materials and polymers with potential long term applications in smart organic electronics, including display- and sensor-technology. Undergraduate and graduate students working on this project will develop a broad range of skills in organic and materials chemistry, as well as engineering. An application will be created to aid in teaching organic chemistry topics in a remote environment. The corresponding website will provide additional broader educational content and will be expanded by uploading videos on mechanistic understanding of organic reactions. Outreach and educational activities will include interactions with local high schools through Scholar’s Day events at the University of Texas at Dallas and through summer research program. At the university level, Professor Biewer will continue to direct summer exchange students from Mexican universities and educate majors throughout the school of natural sciences and mathematics on the topic of functional materials and polymers.<br/><br/>The ability to externally modulate optoelectronic properties of pi-conjugated supramolecular assemblies and polymers, while maintaining conformational demands needed for optimal solid state-performance, is an important challenge for modern organic electronics. This project will focus on the synthetic aspects of the incorporation of a novel photochromic unit based on a bicyclic aziridine ring system into functional thiophenes. Specific objectives will concentrate on (a) the synthesis of semiconducting small organic molecules with a donor-acceptor-donor framework that contains a bicyclic aziridine unit conjugated to the thiophene core, (b) modifications of the conjugated core connected to the bicyclic aziridine unit to maximize change in mobility in photochromic states and (c) incorporation of small photochromic molecules into optoelectronic devices to create smart devices upon application of light. Organic synthetic strategies will be complemented by computational modeling. The knowledge gained will likely be applicable to the functionalization of polythiophenes and other pi-conjugated polymers, in general. The research has the potential to yield new insights into various structure-property relationships of bicyclic aziridine photoswitches and their ability to influence the electronic properties of organic electronics. Designing synthetic methods to incorporate the bicyclic aziridine unit within a conducting material, in conjunction with the electronic mobility along the backbone, may allow the creation of stimuli responsive organic materials and polymers.<br/><br/>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.