(260f) Polymers and Light: Towards Advanced, Photoresponsive Materials

Light induced reactions including photopolymerizations have been explored and utilized since the time of the ancient Egyptians; however, development of new photoresponsive materials, methodologies and applications continues at an ever more rapid pace. Light induced reactions are ubiquitous because they are far more energy efficient than their thermal counterparts, are typically performed in a solventless manner that is more environmentally compatible, occur rapidly at ambient conditions, and they can be controlled in both time and space.

Here, we will focus on two distinct vignettes related to our work on light induced reactions including the development of a bistable material that exhibits controlled, photoinduced transitions from a viscoelasetic fluid to an elastic solid upon exposure to light. This work on covalent adaptable networks (CANs) incorporate dynamic covalent bonds as crosslinks within the network that respond to light to (de)activate the dynamic bond character. These materials are able to change shape and stress-state when exposed to light, facilitating application as novel optical and actuating materials. Using thiol-thioester exchange chemistry, we will discuss the formation of a material that is capable of undergoing recycling, healing, and enhanced toughness of materials based on the photo(de)activated dynamic covalent chemistry. Ultimately, the potential for CANs-based materials to impact numerous materials applications will be presented in light of their distinctive array of material properties.

Secondly, we will present a novel approach to the fabrication of semicrystalline thermoplastic polymers via photopolymerization for potential use in additive manufacturing. Thermoplastic materials produced from photopolymerization processes are notoriously difficult to produce efficiently or rapidly and typically lack robust mechanical properties. These attributes tend to make them impractical for light-based additive manufacturing (3D printing) techniques such as stereolithography (SLA). Here, linear semi-crystalline, thiol-ene photopolymer systems will be discussed that form in seconds at low irradiation intensities and exhibit remarkable mechanical properties such as high elongations to break and toughness while also maintaining the capacity to melt and form a relatively low viscosity liquid for 3D printing applications as casting materials.