Polymer Degradation by Synergistic Dual Stimuli: Base Interaction and Photocatalysis to Unlock a Boron Pendant Trigger for Main-Chain Scission

Abstract

We used the carbon−boron (C−B) bond of a vinyl boronate unit as a trigger site to achieve the main-chain degradation of the copolymer through radical generation from the C−B trigger by the addition of a base (e.g., sodium methoxide) for interaction with Lewis acidic boron and subsequent photocatalysis with an organic photocatalyst. The C−B bond in the side chain and the carbon−carbon (C−C) bond in the main chain of the copolymers are thermally stable, but the copolymer underwent main-chain degradation via a β-scission triggered by unlocking the C−B bond through the synergistic dual stimuli for radical generation. The degradation was temporally controllable by turning the light on and off, and the significance of the C−B bond for the triggering degradation was demonstrated by control experiments and gel degradation.

Photocatalytic Upcycling and Depolymerization of Vinyl Polymers

“…[27] In an alternative co-monomer approach, Ouchi, Nishikawa and co-workers employed a vinyl boronate unit to trigger the mid-chain degradation of polymethacrylic copolymers (Figure 5c). [28] This was achieved by synergistically utilizing a dual stimulus including base activation and photocatalysis under blue light irradiation. An impressive yield of 87 % was reported when poly(butyl methacrylate) copolymers were employed as the starting material.…”

“… (a) Literature summary of Poly(acrylate) photo‐degradation, (b) Poly(acrylate) degradation via sequential dehydrodecarboxylaton and ozonolysis, [30] Copyright 2023, American Chemical Society and (c) dual catalytic degradation of poly(acrylates) containing vinyl boronate unit, [28] Copyright 2023, American Chemical Society.…”

Mechanism-Guided Discovery of Cleavable Comonomers for Backbone Deconstructable Poly(methyl methacrylate)

“…Vinyl polymers, which account for half of all polymers produced, are limited in their deconstructability because of their carbon–carbon backbones, which has driven the development of CCs − or postpolymerization methods − to install cleavable bonds. Because a large fraction of vinyl polymers are synthesized industrially through radical polymerization, various classes of CCs that are compatible with this process have been developed via three main approaches: (1) copolymerizing dioxygen to introduce cleavable peroxy groups; − (2) using comonomers with functional groups that can generate radicals in the polymer backbone to trigger deconstruction; − and (3) employing comonomers capable of radical ring-opening polymerization (rROP) to introduce cleavable functionality. , Among these approaches, rROP CCs have been extensively studied, as they offer molecular tunability and enable a variety of deconstruction mechanisms.…”

Implementing a Doping Approach for Poly(methyl methacrylate) Recycling in a Circular Economy

“…Alternative approaches to PMMA degradation involve copolymerizing MMA with redox-active 33,34 or halogencontaining monomers. 35,36 These copolymers can undergo side chain scission upon photoinduced or transition-metalcatalyzed single-electron transfer (SET), resulting in lower molecular weight oligomers (Scheme 1C).…”

“…Alternative approaches to PMMA degradation involve copolymerizing MMA with redox-active , or halogen-containing monomers. , These copolymers can undergo side chain scission upon photoinduced or transition-metal-catalyzed single-electron transfer (SET), resulting in lower molecular weight oligomers (Scheme C). However, these methods have not yet demonstrated the capability to recover the monomer, a critical step for achieving a closed-loop recycling process for PMMA.…”