Degradable Vinyl Random Copolymers via Photocontrolled Radical Ring‐Opening Cascade Copolymerization**

Abstract

Degradable vinyl polymers by radical ring-opening polymerization are promising solutions to the challenges caused by non-degradable vinyl plastics. However, achieving even distributions of labile functional groups in the backbone of degradable vinyl polymers remains challenging. Herein, we report a photocatalytic approach to degradable vinyl random copolymers via radical ring-opening cascade copolymerization (rROCCP). The rROCCP of macrocyclic allylic sulfones and acrylates or acrylamides mediated by visible light at ambient temperature achieved near-unity comonomer reactivity ratios over the entire range of the feed compositions. Experimental and computational evidence revealed an unusual reversible inhibition of chain propagation by in situ generated sulfur dioxide (SO 2 ), which was successfully overcome by reducing the solubility of SO 2 . This study provides a powerful approach to degradable vinyl random copolymers with comparable material properties to non-degradable vinyl polymers.

Photocatalytic Direct Decarboxylation of Carboxylic Acids to Derivatize or Degrade Polymers

“…It is important that the reactive triggers for cleavage are consistently incorporated throughout the backbone to prevent the formation of large nondegradable fragments. [29] Thus, in our system, the consistent incorporation of MAA triggers into polymer chains was integral for attaining optimal degradation. Promisingly, the pseudo-first-order kinetics plot of MMA and MAA, during copolymerization to synthesize P(MMA-co-MAA) 10% , confirmed that the two monomers reacted at nearly identical rates (Figure S4).…”

“…This has been performed by cleaving C−S linkages in the end groups of polymers synthesized by RAFT or terminal C−Cl bonds to form chain‐end radicals that can then unzip the polymer backbone [27] . An alternative method that does not rely on chain‐end triggers is the incorporation of hydrolysable groups into the polymer chain through radical ring‐opening copolymerization with thionolactones, macrocyclic allylic sulfones, or cyclic ketene acetals [28, 29] . Additionally, comonomers that can generate carbon‐centered radicals and subsequently lead to cleavage of adjacent C−C bonds may be integrated in poly(meth)acrylate backbones to achieve degradation [12, 30] .…”

“…Direct O−H cleavage of pendent carboxylic acids and ensuing release of CO 2 leads to tertiary radicals on the polymethacrylate backbone that initiate β ‐fragmentation, thereby degrading the chain (Figure 3A). It is important that the reactive triggers for cleavage are consistently incorporated throughout the backbone to prevent the formation of large nondegradable fragments [29] . Thus, in our system, the consistent incorporation of MAA triggers into polymer chains was integral for attaining optimal degradation.…”

“…[27] An alternative method that does not rely on chain-end triggers is the incorporation of hydrolysable groups into the polymer chain through radical ringopening copolymerization with thionolactones, macrocyclic allylic sulfones, or cyclic ketene acetals. [28,29] Additionally, comonomers that can generate carbon-centered radicals and subsequently lead to cleavage of adjacent CÀ C bonds may be integrated in poly(meth)acrylate backbones to achieve degradation. [12,30] We demonstrate that this approach is especially facile and effective when MAA is used to form backbone radicals.…”

Synthesis and Degradation of Vinyl Polymers with Evenly Distributed Thioacetal Bonds in Main Chains: Cationic DT Copolymerization of Vinyl Ethers and Cyclic Thioacetals

“…Among them, copolymerization of heteroatom‐containing cyclic monomers with common vinyl monomers, by which labile carbon‐heteroatom bonds can be introduced via ring opening of the cyclic structures, is one of the most efficient methods [23–26] . Various cyclic compounds, which are copolymerizable via ring‐opening reactions, have been developed to date and include cyclic ketene acetals, [27–40] thionolactones, [41–47] and cyclic allylic sulfur compounds [48–52] for radical polymerization as well as oxiranes, [53, 54] cyclic acetals, [55, 56] hemiacetal esters, [57] and 1,3‐dioxa‐2‐silacycloalkanes [58] for cationic polymerization.…”