Mechanisms of Degradation for Polydisulfides: Main Chain Scission, Self-Immolation, Or Chain Transfer Depolymerization

Abstract

Organic polydisulfides hold immense potential for the design of recyclable materials. Of these, polymers based on lipoic acid are attractive, as they are based on a natural, renewable resource. Herein, we demonstrate that reductive degradation of lipoic acid polydisulfides is a rapid process whereby the quantity of added initiator relative to the polymer content defines the mechanism of polymer degradation, through the main chain scission, self-immolation, or "chain transfer" depolymerization. The latter mechanism is defined as the one during which a thiol group released through the decomposition of one polydisulfide chain initiates depolymerization of the neighbor macromolecule. The chain transfer mechanism afforded the highest yields of recovery of the monomer in its pristine form, and just one molecule of the reducing agent to initiate polymer degradation afforded recovery of over 50% of the monomer. These data are important to facilitate the development of polymer recycling and monomer reuse schemes.

Biological applications of lipoic acid-based polymers: an old material with new promise

“…2D). Notably, PLA is susceptible to reduction and depolymerization, 47 making it a promising candidate for non-invasive drug delivery. 48 Some studies have shown that the structures of PLA depend on the nucleophilicity of the initiators.…”

Positioning dynamic polymeric materials within the modern polymer economy: From application to recycling and circularity

“…Disulfide bonds are known to be easily activated by light or heat, promoting homolytic bond cleavage or metathesis reactions without an external catalyst, 107,109,124 although catalysts are often employed to accelerate reaction kinetics. Polydisulfides formed from the ROP of strained cyclic disulfides undergo CRM 125,126 via a variety of mechanisms including anionic-, 127,128 cationic-, 129,130 and radical-mediated 131,132 pathways (Figure 7). A potential disadvantage is that the efficiency of CRM can be highly dependent upon reaction conditions leading to a wide-range of monomer recovery ($20-70%) due to complex depolymerization processes proceeding via mixed mechanisms such as chain-scission or self-immolation which can both be influenced by chain-transfer events.…”

“…A potential disadvantage is that the efficiency of CRM can be highly dependent upon reaction conditions leading to a wide-range of monomer recovery ($20-70%) due to complex depolymerization processes proceeding via mixed mechanisms such as chain-scission or self-immolation which can both be influenced by chain-transfer events. 125 Nevertheless, polydisulfides feature synthetic simplicity coupled with functional complexity [133][134][135] via versatile architectural and structural adjustments, and thus can afford practical polymeric materials such as highperformance degradable adhesives. 136 Polythioesters 137 that are synthesized from the ROP of cyclic thiolactones are another class of highly dynamic DCPs that can be efficiently depolymerized (>90% monomer recovery) under mild conditions, 138 and they also feature an unusual set of performance-advantaged properties which are comparable to polymer composites such as high thermal stability, crystallinity, strength, and ductility.…”

“…Polydisulfides formed from the ROP of strained cyclic disulfides undergo CRM 125,126 via a variety of mechanisms including anionic‐, 127,128 cationic‐, 129,130 and radical‐mediated 131,132 pathways (Figure 7). A potential disadvantage is that the efficiency of CRM can be highly dependent upon reaction conditions leading to a wide‐range of monomer recovery (~20–70%) due to complex depolymerization processes proceeding via mixed mechanisms such as chain‐scission or self‐immolation which can both be influenced by chain‐transfer events 125 . Nevertheless, polydisulfides feature synthetic simplicity coupled with functional complexity 133–135 via versatile architectural and structural adjustments, and thus can afford practical polymeric materials such as high‐performance degradable adhesives 136 .…”