This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
The formation of crosslinked thermosetting polymers is ubiquitous in our society in applications such as coatings, adhesives, composite materials, dental materials and rapid prototyping. Unfortunately, the same crosslinked structure that is the origin of many of the desirable mechanical and thermal properties results in the polymer shape and properties being fixed upon polymerization, traditionally requiring degradation of the crosslinks to change either. Additionally, the polymerization process itself leads to significant stress development and ultimately warping, material failure, and the requirement of complex curing processes.
The PI plans to develop monomers that polymerize to form a new material class referred to as Covalent Adaptable Networks (CANs). These materials combine the advantageous properties of covalent networks with the ability to reverse the polymer network structure on demand. Once these networks are formed, he will demonstrate and understand the various properties that can be achieved by subsequent adaptation through controlled reactions within the polymer network, as triggered either by uniform or patterned exposure to light, by temperature changes, or by exposure to an electromagnetic field. Polymeric materials such as these that are adaptable and able to respond 'on demand' with control of stress, shape, plasticity and composite organization are critical to the development of adhesives, thermosetting composite materials, biomaterials, polymeric coatings, and metamaterials.
The PI plans to expand the capabilities of crosslinked polymer networks by this synthesis, characterization, and development of externally triggerable CANs. These advances are achieved by developing materials and processes that enable polymerization, network reversibility, flow, shape memory, crack healing, and composite organization upon exposure to heat, light, or electromagnetic fields. This research program is divided into four principal aims: (i) Design and synthesize new functional monomers that contain allyl sulfides (AS) so that the benefits of AS-based adaptable networks are expanded to a broader range of conventional thermosets, (ii) Synthesize multifunctional Diels-Alder (DA)-based polymer networks in which the polymerization and reversible crosslink formation are controlled by exposure to an electromagnetic field, either concurrent with or after the polymerization, (iii) Develop and optimize reaction conditions to form patterned composite metamaterial structures from the DA-based polymer networks, and (iv) Use the aforementioned research as a means for training a diverse group of at least 10 undergraduate students and 4 graduate students in the discovery learning process and in the fields of polymer science and reaction engineering. Transformational discoveries will occur in regards to metamaterials fabrication, reversible polymer network design, and remotely controllable polymer network structures.
Intellectual Merit
The achievement of these goals could lead to advances that provide a foundation for future technology developments. Specifically, this research will establish a new range of available crosslinked materials and reaction methodologies that are appropriate for the formation of a wide range of polymer network structures. These networks will be valuable in ascertaining the fundamental structure of crosslinked polymers, as both the microscopic and macroscopic nature of the network are controllable. New techniques will also be developed to reduce polymerization induced shrinkage stress. The coupling of polymerization kinetics, highly localized heat transfer, and Brownian motion of particulates as necessary for metamaterial formation will yield significant intellectual advances.
Broader Impact
Developing this new class of polymeric materials helps to overcome a problem with crosslinked polymers by providing a means for reversibly controlling the shape, stress, and strain of crosslinked networks post-polymerization. With the hysteresis heating, one will be able to remotely eliminate fatigue and facilitate crack healing in structural thermosets and composites and the patterned exposure of the DA-based CANs will enable complex 3D composites to be formed with an almost infinite array of possible material properties. Applications in processes as varied as structural adhesives, 3D prototyping, MEMS, dental materials, optical materials and composite materials all could benefit from the successful completion of this work. The number and diversity of the graduate students impacted by the research will be heightened by interaction with the Department of Education GAANN program that the PI currently directs. Undergraduate students will participate directly in the research through independent study projects and research experiences for undergraduate grants.
