Carbon-Resource Recovery from Vinyl Polymers of Cyclic Ketene Acetal Esters Using High-Temperature Water

Abstract

Vinyl polymer prepared from 2-methylene-4H-benzo[d][1,3]dioxin-4-one (MBDO), a cyclic ketene acetal ester, is a chemically recyclable polymer that is hydrolyzed to salicylic acid (SA) and acetic acid (AA). Despite this potential, the polymer, poly-MBDO, required a strong acid or base in organic solvent for the hydrolysis. In this study, we report the quantitative conversion of poly-MBDO to phenol by treatment in high-temperature water. Hydrolysis of poly-MBDO afforded SA, which underwent rapid decarboxylation to phenol. For example, poly-MBDO quantitatively afforded phenol upon heating in water at 300 °C for 5 min and freeze-drying. Although the hydrolysis of the main chain was incomplete, the products were volatile and removed by drying the reaction mixture, leaving the residue of pure phenol. Since SA is industrially synthesized from phenol and CO₂, the synthesis of poly-MBDO from phenol is in principle possible. The quantitative conversion of poly-MBDO to phenol can also be considered as carbon-resource recovery, since phenol is a raw material for various fine chemicals.

The development of degradable polymers and their degradation methods are important for resource recovery. Herein, phenol was quantitatively recovered from a vinyl polymer of cyclic ketene acetals using high-temperature water.