Dissolving used rubber tires

Abstract

Reductive silylation cleaves S–S crosslinks in used automotive rubbers, allowing recovery of polymeric oils in up to 93% yield. The oils can undergo oxidative crosslinking to give new elastomers, closing the loop for sulfur-cured rubbers.

Reversible Redox Crosslinking of Thiopropylsilicones

“…[ 6 ] We recently demonstrated that the automobile rubber—crosslinked by oligosulfides—could be converted to polymeric oils by reduction of the S–S bonds. [ 7 ] Could such a redox process be the basis of reusable thermoset silicone elastomers?…”

“…In previous work, we reported a versatile, inexpensive method to reduce organic disulfide bonds with hydrosilanes. [ 13 ] We were interested to apply this method reversibly in redox sensitive silicone polymer networks.…”

“…The thiol starting material, initially protected as a silyl sulfide SiS , was recovered after deprotection. While a report suggests that the hydrolysis of Si–S bonds should be very facile, based on observations with Me 3 SiSSiMe 3 , [ 25 ] we found it was necessary to hydrolyze the SiS products in water/isopropanol (IPA) [ 13,26 ] to regenerate the thiol; the byproduct linear tetrasiloxane, which is perceived to be safer in use than related cyclic tetrasiloxanes, was removed by evaporation (Figure 1C and Figure S5, Supporting Information). The 1 H NMR spectra of the recovered oils were identical to the thiopropyl silicone starting materials (Figure S9, Supporting Information).…”

A Review of Heterolytic Synthesis Methodologies for Organotri- and Organotetrasulfane Synthesis

“…16 Cyclic tri-and tetrasulfanes are also known to be available using methodology A, and have been fully reviewed, 1 but once again, mixtures of polysulfanes are invariably produced as with the acyclic variants (Scheme 1, entries 4 and 5). 17,18 Scheme 1 illustrates entries 1-5 based on examples from the last twenty years or so.…”

When Attempting Chain Extension, Even Without Solvent, It Is Not Possible to Avoid Chojnowski Metathesis Giving D3

“…In his extensive and elegant studies of reduction of carbonyl groups, Piers showed that it was also a potent catalyst for hydrosilane reductions [ 17 ]. We used M H M H in the presence of BCF to reduce the sulfur crosslinks in automobile rubber tires, permitting reuse of the organic constituents [ 19 ]. When using HSiEt 3 in the presence of BCF, Piers et al originally reported that over-reduction of carbonyl groups led first to silyl ethers and then to alkanes plus disiloxanes.…”