Reactive Microgels: Small but Smart Soft Materials

Significance 

Recent technological advances have unveiled the broad applicability of reactive polymers in various fields, including: organic electronics, biotechnology and in medicine. In addition, recently published works have highlighted that the level to which the reactive groups can be addressed provides a facile way to impart stimuli responsiveness/specific selectivity, which is vital for applications that take advantage of the reversible incorporation of guest molecules, stimuli responsive deformations, selective separation of similarly sized biomolecules, or bioinspired self-healing of mechanical and structural properties. As such, microgels based on reactive polymers have become popular with researchers due to their excellent attributes. To date, there has been several published reports describing the preparation of reactive polymeric microgels. Unfortunately, these reports merely highlight the broad interest in developing novel and versatile microgels that can be synthetically tailored and reactively modified to control their structure and properties. Worse off, there is no published work elucidating on the fabrication of reactive microgel using azlactone-containing block copolymers.

Recently, Professor Xu Wang at Shandong University in collaboration with Dr. Jesse L. Davis, Dr. Bethany M. Aden, and Professor S. Michael Kilbey, II at University of Tennessee and Dr. Bradley S. Lokitz at the Oak Ridge National Laboratory synthesized azlactone-based microgels by successive self-assembly of PVP-b-PVDMA block copolymers in solution. In addition, they modified the resulting nano-assemblies by cross-linking in a selective fashion. Their work is currently published in the research journal, Macromolecules.

The research method employed commenced with the synthesis of PVDMA and PVP-b-PVDMA block copolymers of different molecular weight that were to be used to investigate the self-assembly and guest loading characteristics. Next, the researchers used a diamine/diiodide to cross-link either the PVDMA or the PVP blocks in the self-assembled aggregates. Lastly, a series of functional primary amines were used to investigate the chemical reactivity of the covalently cross-linked PVP-b-PVDMA block copolymers microgels.

The authors observed that the DAB-cross-linked block copolymer microgels swelled in THF, thereby suggesting the formation of a stable, three-dimensional network structure. They also noted that the azlactone-containing block copolymer microgels provided an attractive platform for applications in a wide range of fields, including imaging, catalysis, molecule separation and guest loading for targeted delivery. This was seen to be due to their ability to be reactively modified in ways that allowed their stability or disassembly characteristics to be tailored.

In summary, the Xu Wang and colleagues study presented a facile method involving self-assembly and cross-linking of azlactone-containing block copolymers as an excellent route to fabricate microgels containing reactive “handles” that could be selectively modified to incorporate additional functionality. Generally, in their approach the surfactant-like nature of PVP-b-PVDMA block copolymers was seen to enable the formation of nanoscale aggregates in solvents selective for PVP blocks, and the size of the self-assembled structure could also be manipulated by tailoring block lengths of the block copolymers. Altogether, the advantages derived from the inherent polymerizability of PVDMA and efficacy of reactive modification without formation of byproducts, make azlactone-containing block copolymers useful as building blocks for functional self-assembled systems or soft scaffolds, which in turn make them applicable as nanoreactors or in sensing applications.

PVP-b-PVDMA – poly(2-vinylpyridine)- block-poly(2-vinyl-4,4-dimethylazlactone)

DAB – 1,4-diaminobutane

Reactive Microgels: Small but Smart Soft Materials - Advanced Engineering

About the author

Xu Wang is a professor in National Engineering Research Center for Colloidal Materials at Shandong University, China. He received his Ph.D. in Polymer Chemistry and Physics from Jilin University, China, in 2012. After graduation, he joined Prof. S. Michael Kilbey II’s research group at the University of Tennessee, Knoxville, TN, USA, working as a postdoctoral research associate for two years. In 2014, he joined Prof. Juntao Luo’s group at State University of New York Upstate Medical University working as a postdoctoral fellow. He moved to Shandong University in 2017. The focus of his current research is in fabricating smart polymer materials, including nanoparticles, microgels, and hydrogels, for therapeutic delivery and bioinspired self-healing.

Please visit http://cis.sdu.edu.cn/wang_lab/HOME.htm for further information.

About the author

Jesse Davis is currently a Senior Development Chemist at Henkel Corporation in their Loctite division of global adhesives and coatings. He received his BSc in Chemistry in 2010 from Georgia Southwestern State University. He completed his PhD in Polymer Science at The University of Tennessee in 2015.

His research focused on investigating how mixtures of architecturally complex, surfactant-like block copolymers can be used to generate new self-assembled constructs and assessing the stability and kinetics of those systems in solution and at surfaces. His research currently focuses on the development of next generation adhesives to fill unmet gaps in the manufacturing and general industries. Jesse is also currently an active member of the ACS Division of Polymer Chemistry Industrial Advisory Board (POLY IAB).

About the author

Bethany Aden is currently a Process Chemist at Eastman Chemical Company in their Cellulose Ester Development Division. In her role, she primarily supports fiber ester manufacturing. Bethany received her BS in Chemistry and Cell and Molecular Biology from the University of Tennessee at Martin. In 2017, she completed her PhD in Polymer Chemistry from the University of Tennessee. Her research focused on the chemical transformation of reactively modified interfacial thin films.

About the author

Brad Lokitz received his Ph.D. in polymer science and engineering from the University of Southern Mississippi and an MBA from the University of Tennessee. He is the User Program Coordinator and a Research Scientist in the Macromolecular Nanomaterials Group at the Center for Nanophase Materials Sciences.

His research activities focus on understanding the assembly-structure-property relationships of well-defined polymers and ultrathin polymer films and analyzing their nanoscale structure and responsiveness using a combination of characterization techniques including neutron scattering.

About the author

S. Michael Kilbey II is a Professor of Chemistry and Chemical and Biomolecular Engineering at the University of Tennessee-Knoxville (UT). He earned his B.S. in chemical engineering from the University of Wisconsin and his Ph.D. in chemical engineering from the University of Minnesota. He began his academic career at Clemson University in 1996, moving to UT in 2008. From 2008-2012 and as a UT/ORNL joint faculty member, he led the Macromolecular Nanomaterials group at Oak Ridge National Laboratory (ORNL). He returned to academia full-time at UT in 2013. Mike is active in the American Institute of Chemical Engineers, where he has served as chair of the Materials Engineering and Science Division, and he was recently honored at UT as the Paul and Wilma Ziegler Professor of Chemistry.

Research in his group is focused on synthesis, self-assembly and interfacial behavior of polymeric materials in thin films and in solution, with particular focus on conjugated, reactive, and responsive polymers.

Reference

Xu Wang, Jesse L. Davis, Bethany M. Aden, Bradley S. Lokitz, and S. Michael Kilbey, II. Versatile Synthesis of Amine-Reactive Microgels by Self-Assembly of Azlactone-Containing Block Copolymers. Macromolecules 2018, volume 51, page 3691−3701.

Go To Macromolecules 2018

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