Synthesis of isohexide-di(ether-ene)s and ADMET polymerization

Abstract

As fossil fuel reserves deplete and greenhouse gases increase, the scientific community is challenged to provide sustainable solutions. Sugar-based isohexides can be modified to prepare a library of isohexide-diene monomers for polymerization. Such isohexide-diene monomers can be subjected to acyclic diene metathesis (ADMET) polymerization to obtain green materials. This paper reports a single-step synthetic protocol to access a small family of isohexide-di(ether-ene)s and the corresponding polymers. The isohexide di(ether-ene)s could be isolated in good to excellent yields under optimized conditions. The resultant isohexide-di(ether-ene)s are potential versatile building blocks for pharmaceuticals and materials science. The synthetic utility of isohexide-di(ether-ene)s was demonstrated by subjecting them to ADMET polymerization using Grubbs first- and second-generation catalysts. The resultant viscous material was evaluated using proton nuclear magnetic resonance and matrix-assisted laser desorption/ionization time of flight mass spectroscopy, which suggest the formation of anticipated ADMET polymers. End-group analysis of the polymers revealed molecular weights of 800–13 800 g/mol. Slight improvement in the molecular weight was observed when benzoquinone was added or when the catalyst was added in two stages. Thus, the analysis of the poly(ether-ene)s suggests that low-molecular-weight polymers were formed under the optimized experimental conditions, and the molecular weight could not be improved beyond a point.