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Advanced Photopolymer Concepts

A one-month, webinar series presented by RadTech and curated by the Photopolymerization Fundamentals Conference

Smart, Responsive Polymers Based on Covalent Adaptable Networks: Photoactivatable Dynamic Covalent Chemistry and Its Applications in Polymer Networks

Dr. Christopher N. Bowman, University of Colorado

Webinar Video
Polymer networks possessing dynamic covalent crosslinks constitute a class of materials with unique capabilities including the capacity for adapting to an externally applied stimulus. These covalent adaptable networks (CANs) represent a paradigm in polymer network fabrication aimed at the rational design of structural materials possessing dynamic characteristics for specialty applications and functions. Here, we explore several distinct approaches to CANs based on photochemically triggered responses. First, those in which the reversible bond formation, based on addition-fragmentation, occurs only during exposure to light will be discussed, enabling polymer network relaxation, photoinduced actuation and shape memory effects, and stress relaxation. Using liquid crystalline elastomer networks of this type, we will demonstrate the solution to fitting a square peg into a round hole, reversibly. Secondly, using thiol- thioester exchange chemistry, we will discuss the formation of a material that is capable of undergoing a bistable transition from a viscoelastic solid to a viscoelastic fluid, induced by light. Using this approach, we demonstrate recyclability, healing, and enhanced toughness of materials based on these types of networks. Ultimately, the potential for CANs-based materials to impact numerous materials applications will be presented in light of their distinctive array of material properties.

3D Photocuring and Photomechanics in Digital Light Processing Additive Manufacturing for Soft Functional Composites and 4D Printings

Dr. H. Jerry Qi, Georgia Institute of Technology

Webinar Video
Digital light process (DLP) is a facile additive manufacturing method and has gained significant development in recent years. It uses a digital micromirror device (DMD) projector to project the light and rapidly cure a thin layer of photopolymer and creates a 3D part in a layer-by-layer manner. Due to the recent development of CLIP and photo-thermal two-stage curing technologies, it has gained great popularity as a rapid high-resolution 3D printing method. Since the degree of cure (DoC) of a photopolymer depends strongly on the light irradiation dose, it is possible to use light intensity (or grayscale) to locally control the DoC and hence the mechanical properties. In this talk, we will introduce several strategies where we use light grayscale to create a part with locally controlled properties for soft functional composites and 4D printing. These include using light grayscale and polymer desolvation to print active origami structures, using light grayscale and two-stage cure to print a highly functionally graded part. We will also introduce our recent efforts of combining DLP methods with other 3D printing technology to create functional composites and for 4D printing applications.

Dentistry as a Driver of Photo-based 3D Printing

Dr. Jeffrey W. Stansbury, University of Colorado Anschutz Medical Campus

Webinar Video
The practice of dentistry was an early adopter of photopolymerization and notably took on the challenge of reliably photocuring thick, highly light attenuating dental composite restoratives under non-ideal conditions, i.e. in the patient’s mouth. Other photopolymers including polymer-modified hybrid materials spanning a range of dental applications are also now in common place use. More recently, the profession has also embraced the concept of digital dentistry in terms of accurate, high-resolution detailing of the dental morphology of individual patients in electronic data files that can then be used in to produce a wide variety of patient-specific items whether through the subtractive process of milling pre-formed blocks of ceramic and polymer-based materials or via the additive manufacturing approach that encompasses several 3D printing techniques. This presentation will highlight the use of photopolymerization-based 3D printing with SLA/DLP and ink jet processes. The intent is to show what is already in widespread use as well as focusing on the challenges and opportunities associated with new photo-printed polymer application areas poised to significantly reshape the dental profession through ongoing progress in printing platforms, software design and materials development that are being pursued very actively.

Pushing the limits of CRP and post-polymerization modification to access new materials

Dr. Brent S. Sumerlin, University of Florida
October 28, 2020, 2:00 PM – 3:00 PM EDT

Registration

As many physical properties of polymers scale with molecular weight, the ability to achieve polymers of nearly inaccessible high molecular weight provides an opportunity to probe the upper size limit of macromolecular phenomena. Yet many of the most stimulating macromolecular designs remain out of reach of current ultra-high molecular weight (UHMW) polymer synthetic approaches. Herein, we show that UHMW polymers of diverse composition can be achieved by irradiation of thiocarbonylthio photoiniferters with long- wave ultraviolet or visible light in concentrated organic solution. This facile photopolymerization strategy is general to acrylic-, acrylamido-, methacrylic-, and styrenic-based monomers, enabling synthesis of well-defined macromolecules with molecular weights in excess of 106 g/mol. The high chain-end fidelity afforded by photoiniferter polymerization conditions facilitated the design of UHMW amphiphilic block copolymers, which were found to self-assemble into micellar morphologies up to 200 nm in diameter.

Block copolymers prepared by reversible-addition fragmentation chain transfer (RAFT) polymerization are often restricted to a specific comonomer blocking sequence that is dictated by intermediate radical stability and relative radical leaving group abilities. Techniques that provide alternative pathways for reinitiation of thiocarbonylthio-terminated polymers could allow access to block copolymer sequences currently unobtainable through the RAFT process. We report a method for preparing “inverted” block copolymers, whereby the traditional order of monomer addition has been reversed through the use of photoiniferter-mediated radical polymerization. Specifically, thiocarbonylthio photolysis of xanthate- and dithiocarbamate-functional macromolecular chain transfer agents (macro-CTAs) led to the direct formation of leaving group macro-radicals otherwise unaffordable by an addition-fragmentation mechanism. We believe this method could provide a route to synthesize multiblock copolymers of synthetically challenging comonomer sequences.

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