(705b) The Development of a Paradigm for the Facile Incorporation of Diels-Alder Moieties

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The Development of a Paradigm for the Facile Incorporation of Diels-Alder Moieties

Kenneth C. Koehler, Christopher J. Kloxin and Christopher N. Bowman

Department of Chemical and Biological Engineering 

University of Colorado at Boulder

424 UCB Room ECCH 111

Boulder, CO 80309
 

Abstract

One of the reactions associated with the “Click” paradigm, the Diels-Alder reaction has come to use in a variety of applications pertaining to polymer chemistry including protecting groups, mendable materials and covalent adaptable networks. Unfortunately, the creation of material making use of the Diels-Alder reaction typically relies upon a trial and error process to select the proper diene/dienophile pair for a given application. To address the downfall of the trial and error method, this work aimed to develop a library containing the thermodynamic and kinetic parameters of select Diels-Alder reactions, allowing for the a priori selection of a diene/dienophile pair for a given application. Using HNMR spectroscopy, this study focused on the determination of thermodynamic and kinetic properties of the Diels-Alder reaction between maleimide and furan carboxylic acids. The impact of changing the substitutional position and proximity of the carboxylic acid group to the furan and maleimide on the thermodynamics and kinetics of the Diels-Alder reaction was investigated. It was found that direct conjugation of the carboxylic acid moiety into the furan ring at the two position allowed for a fast Diels-Alder reaction with a low equilibrium conversion. Substituting the carboxylic acid group at the three position resulted in a slower Diels-Alder reaction with a much higher equilibrium conversion. Placement of the carboxylic acid in the two position while removing conjugation to the furan ring with a aliphatic spacer granted both, a fast reaction and high conversion. The impact of changing the length of the carbon chain separating the maleimide ring from the carboxylic acid group was also studied. It was found that as the chain between the maleimide ring and carboxylic acid group increased, the Diels-Alder reaction rate remained relatively unchanged, however the equilibrium conversion increased. With the over-arching goal of using maleimide and furan moieties to create materials, the impact of incorporating the furan and maleimide carboxylic acids onto another species, t-butyl glycine, had on the thermodynamic and kinetic properties was studied. In general, it was found that maleimide and furan carboxylic acids had similar reaction rates and thermodynamic properties as compared to their t-butyl glycine coupled counterparts.