Enhanced Degradation of Vinyl Copolymers Based on Lipoic Acid

Abstract

The introduction of degradable units into the backbone of commodity vinyl polymers represents a major opportunity to address the societal challenge of plastic waste and polymer recycling. Previously, we reported the facile copolymerization of α-lipoic acid derivatives containing 1,2-dithiolane rings with vinyl monomers leading to the incorporation of degradable S–S disulfide bonds along the backbone at relatively high dithiolane monomer feed ratios. To further enhance the recyclability of these systems, here we describe a facile and user-friendly strategy for backbone degradation at significantly lower dithiolane loading levels through cleavage of both SS and SC backbone units. Copolymers of n-butyl acrylate (nBA) or styrene (St) with small amounts of either α-lipoic acid (LA) or ethyl lipoate (ELp) dissolved in DMF were observed to undergo efficient degradation when heated at 100°C under air. For example, at only 5 mol% ELp, a high molecular weight poly(ELp-co-nBA) (M _n  = 62 kg mol⁻¹) degraded to low molecular weight oligomers (M _n  = 3.2 kg mol⁻¹) by simple heating in DMF. In contrast, extended heating of either poly(nBA) or poly(St) homopolymers under the same conditions did not lead to any change in molecular weight or cleavage of the C–C backbone. This novel approach allows for the effective degradation of vinyl-based polymers with negligible impact on properties and performance due to the low levels of dithiolane incorporation.