Photopolymerization and characterization of modified thiol-ene networks

Bradley James Sparks, University of Southern Mississippi

Abstract

Photopolymerization provides a unique ability to control variables typically uncontrollable using traditional thermally initiated polymerization, thus leading to its use in a broad range of commercial operations. Many of the traditional photopolymers suffer from several setbacks, including oxygen inhibition, unwanted stress buildup which leads to bulk shrinkage, etc., which ultimately lead to diminished polymer performance. The photopolymerization of multifunctional thiols and alkenes has been shown to provide a means to improve upon the weaknesses of traditional photoinitiated polymerizations. The free radical polymerization of thiol and -ene monomers occurs via a series of free radical chain transfer events, as a result, they do not suffer from oxygen inhibition or unwanted stress buildup during network formation. Crosslinked thiol-ene networks, however, are not characterized as having high moduli or glass transition temperatures due to their chemical makeup (i.e., flexible thio-ether linkages). In this work, we describe the modification and characterization of thiol-ene networks using various functional materials (either covalently or physically mixed) in an effort to improve the physical properties of the network. In the first study, organic-inorganic hybrid materials containing stable silanol functionalities were designed by incorporating cyclic tetravinyl siloxanetetraols into photopolymerized polymer networks via the thiol-ene reaction, with the intent of tailoring the thermal and mechanical properties of the resulting materials. The second study focused developing structure-property relationships of a modified thiol-ene network as a function of catechol concentration. Ultimately, the catechol functionality played a role in improving the physical properties (i.e., thermomechanical, mechanical and adhesion) of the crosslinked networks. In the third study, graphene oxide materials (graphene oxide and reduced graphene oxide) were incorporated into three different thiol-ene networks at various loading levels. The mechanical and thermomechanical properties of the networks were investigated to determine the effect of graphene oxide loading percentage on the physical properties of the materials. In the final study, superhydrophobic films were prepared, where a hybrid organic-inorganic thiol-ene materials was sprayed onto a surface using an airbrush. Using the combination of the spraying technique and the incorporation of functionalized silica nanoparticles, a film with dual-scale roughness on the micro- and nano-scale was achieved resulting in the formation of superhydrophobic films with self-cleaning properties.