Reaction between 1,3,5‐Triisopropylbenzene and Elemental Sulfur Extending the Scope of Reagents in Inverse Vulcanization

Abstract

Inverse vulcanization utilizes an organic compound as reagent for crosslinking elemental sulfur to result in corresponding polymeric material with a high sulfur content. This work, employing 1,3,5-triisopropylbenzene (TIPB) as the reagent, demonstrates the first attempt on extending the scope of crosslinking agents of inverse vulcanization to saturate compounds. Under nuclear magnetic spectroscopic analysis, the reactions between TIPB and elemental sulfur take places through ring-opening reaction of S 8 resulting in sulfur radicals at sulfur chain ends, radicals transferring to isopropyl groups of TIPB, and radical coupling reactions between carbon radicals and sulfur radicals. The obtained products are similar to the sulfur polymers from conventional inverse vulcanization processes and show self-healing property.

On the Mechanism of the Inverse Vulcanization of Elemental Sulfur: Structural Characterization of Poly(sulfur-random-(1,3-diisopropenylbenzene))

“…As the primary microstructure of this polymer is composed of the thiocumyl units, for technical communicative purposes, it is recommended to present the chemical repeating unit of poly(S-r-DIB) prepared by inverse vulcanization as shown in Figure 1b. The important role of allylic hydrogen abstraction in the inverse vulcanization of DIB has further been supported by a recent report on the inverse vulcanization of tris-isopropylbenzene 11 where abstraction of benzylic H-atoms has afforded polymeric materials with NMR spectroscopic profiles similar to those described herein. Finally, it is further recommended that all new sulfur derived polymers (i.e., inverse vulcanized polymers) include both NMR spectroscopic characterization of the polymer (either solution or solid state), along with analytical structural characterization of degraded organic comonomer units, as detailed in this report.…”

“…A diverse range of unsaturated organic comonomers have been investigated for inverse vulcanization in the past decade, which include styrenes, α-methyl styrenes, cyclic olefins, natural olefinic products, allyls, alkynes, and benzoxazines, 2,7,9,10 as well as aliphatic benzylic comonomers. 11 obstacle in screening new organic comonomers is poor miscibility with liquid sulfur, which greatly narrows the scope of accessible comonomers for inverse vulcanization. Recently reported efforts to expand the scope include the use of liquid sulfur resins as prepolymers for dynamic covalent polymerization (DCP), 12−16 organic nucleophilic activators, 14,17,18 organo/metal salt dithiocarbamate catalysts, 19,20 or photoinduced processes.…”

“…A major advance in this area was the development of a new polymerization process termed inverse vulcanization, which enabled the bulk copolymerization of molten elemental sulfur and unsaturated comonomers without the need for externally added initiators or solvents. ,,,, The inverse vulcanization process proceeds at elevated temperatures where the equilibrium between S 8 (also other cyclic forms) and ring-opened sulfur diradicals drives the polymerization (Figure ). A diverse range of unsaturated organic comonomers have been investigated for inverse vulcanization in the past decade, which include styrenes, α-methyl styrenes, cyclic olefins, natural olefinic products, allyls, alkynes, and benzoxazines, ,,, as well as aliphatic benzylic comonomers . A common major obstacle in screening new organic comonomers is poor miscibility with liquid sulfur, which greatly narrows the scope of accessible comonomers for inverse vulcanization.…”

Manipulating Inverse Vulcanization Comonomers to Generate High-Tensile-Strain Polymers

“…Many plant-based oils have also been considered for similar applications. , Recent research challenges the original idea that the progress of the IV reaction requires the presence of alkene bonds to react with sulfur. Lai et al have demonstrated the reaction of 1,3,5-triisopropylbenzene with sulfur, noting that this monomer contains no alkenes and sulfur bonds directly to alkyl units . The Pyun group have also built on this work by reassessing their original structure for 1,3-diisopropenylbenzene, demonstrating a different structure formation than was previously suggested .…”

“…Lai et al have demonstrated the reaction of 1,3,5triisopropylbenzene with sulfur, noting that this monomer contains no alkenes and sulfur bonds directly to alkyl units. 21 The Pyun group have also built on this work by reassessing their original structure for 1,3-diisopropenylbenzene, demonstrating a different structure formation than was previously suggested. 22 This revisiting of old hypotheses is of great importance for understanding this complex process.…”