Modern Approaches for Multifunctional Hydrolyzying Thiol-ene Networks
Marine fouling has been an expensive and time-consuming process for navies and fishermen by the accumulation of marine algae and animals on artificial surfaces. Many coatings have been proposed to combat marine fouling in efforts to extend the lifetime of objects immersed in sea water. However, all coatings tested have either failed to resist fouling for a significant length of time or have released toxins into the environment. We have investigated an environmentally friendly approach to address the problem of marine fouling through the synthesis and preparation of a biocidal and a self-polishing coating. Both novel monomers were prepared containing ene functionality cable of a radical step growth polymerization with a thiol functional group to form rapid homogenous thiol-ene networks in the presence of oxygen.
Self-polishing polymer networks were prepared that could result in a fouled polymer surface being released from the network of a coating exposing a pristine polymer underneath. A novel hydrolyzing monomer was created through a substitution reaction allowing for the incorporation of hydrolytically unstable bonds into a thiol-ene network. Kinetic rates of polymer hydrolysis were investigated to understand and manipulate the rate of polymer degradation in aqueous environments. Multiple characterization techniques were employed revealing surface erosion was taking place allowing for the development of a self-polishing polymer surface.
Self-decontaminating networks were investigated as means to resist marine fouling by creating a surface capable of killing small organisms on contact. An addition reaction was used to synthesize a series of biocidal quaternary ammonium compound (QAC) by varying the alkyl chain on the positively charged nitrogen center. Minimum inhibitory testing was performed on each QAC showing high biocidal activity of each QAC in solution. Each thiol-ene film containing QAC was able to maintain a high biocidal activity at 5 wt.% addition of the prepared QAC.
All films investigated were thoroughly characterized for physical, mechanical, thermal, and surface properties using standard techniques. In both the biocidal and hydrolysable investigation polymerization kinetics and corresponding thiol monomers were held consistent. In efforts to tailor coating properties a fundamental thiol-ene investigation was performed to analyze adhesion strength and thiol-ene network properties by varying functionality and network density of thiol and ene monomers. Mechanical and physical properties of thiol-ene formulations appeared to correspond to substrate adhesion with formulations exhibiting higher glass transitions (T g ), toughness, and stress at breakage values also showing the highest substrate adhesion. Results of the fundamental thiol-ene study should be beneficial in tailoring properties of thiol-ene networks in future studies.