Universal Strategy for the Synthesis of Sequenced Copolymers with Molecular Weight Control

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Technological advances in medicine, energy, and electronics often depend on the availability of suitable materials. Polymers, which are long chains made up of hundreds of monomer subunits, are an important class of materials employed in many of these fields. Although the properties of biological polymers, like proteins and DNA, are derived from sequence, few methods for preparing non-biological polymers with controlled sequences exist. Professor Tara Meyer of the University of Pittsburgh is supported by the Macromolecular, Supramolecular and Nanochemistry Program of NSF to develop a new method for preparing polymers from sequenced monomer units. Using this method a large number of polymers with a range of properties can be constructed by rearrangement of a limited number of monomer subunits, e.g., ABABABAB... vs. AABBAABB... . The method employed herein offers important advantages over the few competing strategies including increased scale, control of chain length, and the potential for the creation of more complex architectures. Undergraduate and graduate education is a significant component of this project. Students are trained specifically in polymer chemistry by participation in the research and more generally in career skills by direct mentoring from Prof. Meyer and through participation in a series of workshops. The workshops, although offered generally to all interested graduate student participants, stress skills and knowledge that are recognized as particularly helpful for students from underrepresented racial, gender, and socioeconomic groups. Entropy-driven ring-opening polymerization (ED-ROMP) of macrocycles with embedded sequences of 3-12 monomers is employed to produce polymers with a periodic display of the encoded sequence and controlled molecular weights. Two new variants of the fundamental ED-ROMP protocol, Selectivity Enhanced (SEED-ROMP) and Deactivation (DED-ROMP), are developed in order to improve molecular weight control, lower dispersities and allow for the preparation of more complex block architectures. By studying the kinetics, molecular weights and dispersities for each process, this research aims to gain a better fundamental understanding of these processes and information important for developing optimized, universal protocols for ED-, SEED-, and DED-ROMP. These methods are applied to the preparation of two distinct classes of sequenced copolymers: biodegradable poly(lactic-co-glycolic acid)s and semi-conducting conjugated arylene vinylenes. Properties related to the targeted application of each system, i.e, bioengineering and optoelectronics, are be measured and compared with those of the starting oligomers and/or the copolymers prepared by direct step-growth coupling of the sequenced oligomers.