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Qianli Rick Chu

 

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Chu Group Research - Sustainable Materials and Photochemistry

Since the dawn of civilization, the development of new materials has been the driving force behind technological advancement, and in the modern era, few materials have had a broader impact than synthetic polymers. However, plastic wastes are also causing severe environmental tribulations both on land and in the sea (e.g., the great pacific garbage patch). Using photoreaction, our research is opening a new gate for making recyclable and/or degradable polymers and their building blocks, such as cyclobutane-containing polymer (CBP) and cyclobutanedicarboxylic acid (CBDA).
Organic Nanomaterials As shown in the figure on the left, construction and characterization of sustainable organic materials is an interdisciplinary pursuit that requires knowledge of not only polymer chemistry but also organic synthesis, photochemistry, and sustainable sciences etc. It is a crucible within which several traditional disciplines are combined to form a new branch of science, thus representing a challenge to researchers. The diverse backgrounds of our group members offer us opportunities to learn from each other about all of the scientific fields necessary for preparing our synthetic targets.


Project I: Sustainable Monomers and Polymers Synthesized by Photoreaction

Our research team has recently synthesized a series of promising biomass-derived cyclocbutane-containing diacids (CBDAs), which are building blocks for making sustainable materials. Our study has shown that using CBDAs in the construction of materials is beneficial not only because they can be produced from renewable starting materials, but also because they have desired thermal, sunlight, and chemical stability. Meanwhile, the four-membered carbon ring structure of CBDAs offers a unique semi-rigid material property. These features of CBDAs allow them to be used directly in making new polymers or be added into known polymer recipes in a certain ratio to alter physical properties such as transparency and glass transition temperature. The successful synthesis of a number of thermoplastic and thermoset polyesters confirmed that CBDAs are useful building blocks in materials. Initial thermal, chemical, and photochemical analyses revealed stabilities of the newly synthesized cyclobutane-containing polymers (CBPs), which are comparable to those of PET. More importantly, the cyclobutane ring in those polymeric structures can be cleaved by using deep UV, sonication, and/or heat. With increasing environmental problems caused by plastic wastes, it is crucial to find facile and scale ways to degrade the diacids at the end of their lives as polymer building blocks.

We have also made a variety of novel polylcyclobutanes stereoregularly from designed multiomers through a photocycloaddition reaction under mild solvent-free conditions. The carbon-carbon single bonds formed stereospecifically during the locally confined [2+2] photopolymerization process were directly revealed by the single crystal X-ray structures of intermediates. One of the key biobased substances used to make these polycyclobutanes is furfural, which can be derived from pentose sugars found within the hemicellulose of a variety of biomass sources, such as corncobs, rice hulls, and sugar cane bagasse.


Project II: Strong and Lightweight Materials (SLIM) for Fuel-Efficient Transportation

A twenty percent reduction in the weight of an automobile will reduce its fuel consumption by ten percent. Replacement of metal with plastic is a proven success. With climate change and energy shortages looming, lighter yet stronger new materials are required to replace the traditional plastic and metal for fuel-efficient transportation.

Our research team has recently reported stereo-regular polymeric ladders and two-dimensional (2D) polymers from symmetric monomers via topochemical polymerization. Ladder and 2D polymers are theorized to be stronger than traditional polymers because each monomer is connected with its neighbors by multiple covalent bonds in an organized way. Moreover, solid-state polymerization offers a unique opportunity to synthesize macromolecules with regio- and stereo-specificity because topochemical reaction proceeds with minimum movement of atoms. Stereoregularity is an important property of polymers with chiral centers that directly determines the performance of the polymeric materials. Stereoregular polymers often have an array of mechanical properties that are superior to those of corresponding non-stereoregular polymers.


Project III: Self-Assembly and Application of Supramolecular Atropisomers

Chiral materials are valuable for their applications ranging from nonlinear optics to chiral separation and catalysis. The construction of chiral materials from achiral molecules is valuable but challenging. Our research group has been exploring one aspect of the challenge by using supramolecular atropisomers.

Supramolecular atropisomer is an achiral molecule with one or more stereogenic axis that shows chirality when it forms aggregates. N,N’,N’’-tris(n-octyl)benzene-1,3,5-tricarboxamide (BTA) with three stereogenic axes is an example. The six atoms within each amide are nearly planar, and each amide group is partially tilted with respect to the core aryl ring to fulfill requirements of the hydrogen bonds’ orientations and close packing of the molecules. Two of the three amides are pointing toward the same direction. The distances of three C−C single bonds connecting the amide groups and benzene ring are approximately 1.51 Å, which is close to the typical bond length of a C−C single bond. However, due to the hydrogen bonds, the amide groups are not free to rotate around the C−C single bond axes in this supramolecular atropisomer, resulting in a three-dimensional chiral conformation fixed in the hydrogen bonded network.
 

 

 

 


 

 

 

 

 

 

The University of North Dakota Grand Forks, ND 58202
Send questions/comments about this web site to the Dr. Qianli Rick Chu.
Tel: 701-777-3941
Email: chu@chem.und.edu

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