Transformation of thio-catechol adhesive chemistry to sustainable thio-guaiacyl chemistry by using masked ortho-quinones as reactive species

• Applicant: Professor Dr. Hans Gerhard Börner
• Subject Area: Preparatory and Physical Chemistry of Polymers
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539647622

The objective of the present proposal is to extend the synthesis route of mussel-inspired thiol-catechol adhesive polymers to more sustainable thiol-guaiacyl adhesives. To achieve this, the chemistry of thiol-quinone Michael polyaddition will be adapted from the use of quinones to masked ortho-quinones. This opens up the monomer toolbox to sustainable monomers and allows, for example, the replacement of Bisphenol A-based bisquinones with Vanillin-based bisguaiacyls, which can be activated to masked ortho-quinones. TCC-polymers with thiol catechol connectivities (TCC) in each repeat unit have been described as potent adhesives. Their synthesis involves the IBX oxidation of bisphenols to bisquinones, and the monomers obtained are reacted with dithiols to form TCC-polymers. The scope of this proposal is to change this chemistry toward sustainable biophenols. For this purpose, bis/tris-guaiacyl monomers will be synthesized based on the available and sustainable vanillic acid. As an alternative to the potentially hazardous IBX chemistry, guaiacyl structures will be directly activated into masked ortho-quinones and polymerized in solution or in bulk via the thiol-masked ortho-quinone Michael polyaddition route, with di-/tri-thiols to form polymers, having analogues thiol-guaiacyl connectivities (TGC). Activation and polymerization will be studied on a model monomer system. Subsequently, a monomer library of di/tri/hexa-functional vanillic acid esters, but also hydrovanilloin, 1,1'-spirobi(indane) derivatives and vanillyldiguaiacyls will be synthesized, activated and polymerized with multithiols. This set of TGC-polymers will be characterized to determine structure-property relationships. The coating and adhesion properties will be investigated, and compared with those of TCC-polymers. This will broaden the range of monomers used to include available compounds from renewable resources and potentially improve both monomer and polymer stability, as guaiacyl structures are less prone to side reactions than to the analogous catechol structures.

• DFG Programme: Research Grants