Vitrimeric Silicone Elastomers Enabled by Dynamic Meldrum’s Acid-Derived Cross-Links

Abstract

Current vitrimer technology uses only a handful of distinct reactions for cross-linking. New dynamic reactions can diversify vitrimer functionality and properties. In this paper, reversible cross-links formed by conjugate addition–elimination of thiols with a Meldrum’s acid derivative enable compression–remolding of silicone elastomers. After 10 remolding cycles, there is no discernible deterioration of mechanical properties (Young’s modulus, T g, rubbery plateau E’), nor is there a change in stress relaxation activation energy. This robust new cross-linker could be implemented in any number of systems that currently use permanent thiol–ene cross-linking, expanding the scope of recyclable materials.

Reprocessable, Reworkable, and Mechanochromic Polyhexahydrotriazine Thermoset with Multiple Stimulus Responsiveness

“…through the reversible depolymerization or exchange reactions of their dynamic cross-links [ 3 , 9 , 10 , 11 ]. So far, a number of CANs based on Michael addition [ 12 , 13 , 14 ], Diels-Alder reaction [ 15 , 16 ], disulfide exchange [ 17 , 18 , 19 ], imine metathesis [ 20 , 21 , 22 ], transesterification [ 23 , 24 , 25 ], olefin metathesis [ 26 , 27 ], silyl ether transalkoxylation [ 28 , 29 ], diketoenamine exchange [ 30 , 31 ], and dioxaborolane metathesis [ 32 , 33 ] have been proposed in the literature. Besides recyclability, many other adaptive properties of CANs were also investigated, such as reconfigurability [ 34 , 35 ], shape memory [ 36 , 37 ], and network topological transformation [ 18 , 25 , 38 ].…”

Covalent Adaptable Networks with Tunable Exchange Rates Based on Reversible Thiol–yne Cross‐Linking

“…In this encouraging prior study, it was shown that the dynamic thiol exchange of thioacetals via retro‐Michael reactions (vinylogous thioesters) was possible, and can thus likely be tuned for interesting applications in the context of dynamic combinatorial libraries . Recently, there has been a surge in reports on CANs that rely on dynamic thiol exchange via reversible thiol‐Michael chemistry, transthioesterification and reversible exchange at a Meldrum's acid alkylidene . As the currently available thiol‐based dynamic chemistries either require exotic reagents, free thiols that are prone to side reactions (such as oxidation), long relaxation times or aqueous basic conditions to allow exchange, we envisaged that the thiol–yne‐derived dynamic thioacetal links could thus provide a quite valuable and complementary addition to the growing toolbox of dynamic thiol‐click chemistries .…”

“…[21] As part of our groupscontinuing interest towards CANs and the exploration and development of new reversible chemistry platforms for their design, we were inspired by the base-catalyzed dynamic equilibria of thiols and activated alkenes.A lthough thiol-ene reactions are long-known in polymer chemistry as click-like bond forming reactions,their reversible nature has only recently been explored in polymer chemistry by Konkolewicz and co-workers (Scheme 1a). [22] Further inspired by recent work by Kalow and co-workers using thioacetals as versatile dynamic cross-links (Scheme 1b), [23] we became intrigued by the possibility of using simple activated alkynes,such as alkynones,directly as crosslinkers for thiol-based monomers and polymers,inastraightforward way resulting in possibly highly dynamic thioacetal linkages,s tarting from very simple precursors (Scheme 1c).…”

Linear Viscoelasticity and Flow of Self-Assembled Vitrimers: The Case of a Polyethylene/dioxaborolane System

“…1 Since then, the literature has focused on altering the exchange reaction (either catalytically controlled or catalyst-free) and adapting chemistries to different polymer backbones. 2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27 Other studies explored the properties of vitrimer composites and the addition of nondynamic cross-links to the network. 14,28,29,30,31,32,33,34,35 These research efforts established that modifying vitrimer chemistry provides a pathway for tuning mechanical properties, 36,37,38 stress relaxation, 39,40,41,42 shape memory, 43,44,45 and the ability to self-heal and adhere to other materials.…”