GOALI: Advanced Thiol-Ene Photopolymerizations

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

ABSTRACT PI: Christopher Bowman and John Woods Institution: University of Colorado Proposal Number: 0626023 Title: GOALI: Advanced Thiol-Ene Photopolymerizations Project Summary Photopolymerization is a rapidly expanding processes for materials production, with more than 20% annual growth in a multibillion dollar industry that is utilized in a broad range of fields. Industry has increasingly turned to photopolymerizations because these reactions provide for extremely rapid, solvent-free curing of polymer coatings. The reactions are more energy efficient than their thermal counterparts and the ability to control polymer formation spatially and temporally has enabled facile ambient curing and photolithographic technologies to be developed. Because of their advantages, these systems are being utilized or explored in industries that range broadly from biomedical implants to printing applications to photolithographic processes to high technology coatings. Despite the broad applicability of photopolymerizations, the traditional (meth)acrylate-based free radical photopolymerization process is limited by an array of drawbacks that include oxygen inhibition, the presence of residual, unreacted monomer, slow curing, and polymerization induced shrinkage and shrinkage stress development. These limitations are all potentially solved by the utilization of thiol-ene-type photopolymerization reactions. The thiol-ene photopolymerization represents a fundamental shift in the mechanism of photopolymerizations in which the reaction proceeds via alternating propagation and chain transfer reactions. This behavior leads to a step growth evolution of the network that is radically mediated with significant advantages related to delayed gelation, limited extractables, overcoming oxygen inhibition, and reduced shrinkage and shrinkage stress. The thiol-ene polymerization itself has been limited by a lack of understanding and a lack of appropriate, commercially available materials. This project is a collaboration between the University of Colorado and Henkel Corporation for the development of thiol-ene photopolymerizations. The research will focus on synthesis and analysis of thiol and ene-based monomers, which will improve the formation of high modulus, high glass transition temperature materials. In addition to synthesizing new, highly functional monomers, a second goal relates to the development of multicomponent thiol-ene photopolymerizations. The delayed gelation apparent in thiol-ene polymerizations because of their step growth characteristic leads to low stress coatings and films; however, further delays in gelation that lead to enhanced reductions in the shrinkage stress will be achieved in multicomponent polymerizations. These developments, in total, will have impact by providing a viable photopolymerization-based alternative to a range of applications that require high glass transition temperature and/or low shrinkage stress materials. Each of these objectives will be accomplished in collaboration with scientists and engineers at Henkel who will evaluate the commercial feasibility of the synthetic approaches, the properties of the newly formed materials, and the potential for these systems in various commercial applications. Broad Impact The technologies developed here have the potential for expanding the range of photopolymer applications in processes as varied as nanoimprint step and flash lithography, dental restoratives, adhesives and high technology coatings will all benefit significantly from these developments. Also, this project will directly impact students including graduate and a range of undergraduate students.