Turning essential oil into a degradable polymer by catalytic oxidation Tatsuya Seko, Naoki Shida, Mahito Atobe Yokohama National University, Japan Phenylpropanoids, which are main ingredients of essential oils, have been attracting attention as renewable aromatic-containing biomass resources owing to their availability and abundant nature, thus expected to replace traditional petrochemical raw materials. In this context, the polymers containing phenylpropanoids via radical or cationic polymerization have been reported. 1), 2) However, the reactivity of phenylpropanoids is low because they contain a β-substituted styrene backbone, thus co-polymerization with other monomers are essential. From these backgrounds, we designed degradable bifunctional monomers containing two phenylpropanoids. We have aimed to develop efficient production of polymers via catalytic oxidative cycloaddition reactions of these bifunctional monomers, inspired by the hole catalytic [2+2] cycloaddition polymerization reaction developed by Bauld in 1990s. 3) In our design of monomers, a siloxane skeleton (–O–Si–O–) was installed as a linker unit in bifunctional monomer, which can be cleaved by treatment with a base, making the polymer degradable. 4) In this work, we demonstrated the synthesis of phenylpropanoids-derived polymer, as well as its on-demand degradation, towards the development of sustainable materials contributed to sustainability of chemical industry. First, we synthesized bifunctional monomers by condensation of two phenylpropanoids and dichlorosilane under basic conditions. Through our optimization for substituents on silyl atom, diisopropyl group was found to be suitable to design stable monomers, and various functionalized monomers were prepared on gram scale. Polymerization reaction was then performed by using catalytic amount of Magic Blue (tris[4-bromophenyl] ammoniumyl hexachloroantimonate) as an oxidant. Single electron oxidation initiated radical cation cycloaddition polymerizations, and desired polymers with cyclobutene backbone was successfully obtained. In this polymer, 71wt% of its contents derives from biomass, indicating the high incorporation of bio-derived ingredients. Furthermore, resulting polymers were degraded by treatment with tetrabutylammonium fluoride (TBAF) under ambient conditions. To gain insights into the oxidative polymerization process, cyclic voltammetry (CV) measurements were performed. CV data indicated that the oxidation potential of monomers determines the efficiency of polymerization reaction. Physicochemical analysis for these polymers and development of photocatalytic polymerization reaction will be discussed in the presentation.
References 1. M. Kamigaito et al., J. Am. Chem. Soc ., 2007 , 129 , 9586-9587.S. Jana et al., Polym. Chem ., 2020 , 11 , 5630. 2. N. L. Bauld et al., J. Phys. Org Chem , 1999 , 12 , 808-818.A. M. Johnson, et al., Nature. , 2020 , 583 , 542–547.
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