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
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
Dentistry as a Driver of Photo-based 3D Printing
Dr. Jeffrey W. Stansbury, University of Colorado Anschutz Medical Campus
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
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.