No 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.

Catalyst free crosslinking of highly branched silphenylene monomers, made using the Piers–Rubinsztajn reaction, leads to high refractive index, soft elastomers.

Hydrosilanes and silicones, catalyzed with B(C6F5)3, may be used to silylate thiols or cleave disulfides giving silyl thio ethers. Alcohols were found to react faster than thiols or disulfides, while alkoxysilanes (the Piers‐Rubinsztajn reaction) were slower such that the overall order of reactivity was found to be HO>HS>SS>SiOEt. The resulting silane and silicone‐protected thio ethers produced from the sulfur‐based functional groups could be cleaved to thiols using alcohols or mild acid with rates that depend on the steric bulk of the siloxane.

Branched silicones possess interesting properties as oils, including their viscoelastic behavior, or as precursors to controlled networks. However, highly branched silicone polymers are difficult to form reliably using a “grafting to” strategy because functional groups may be bunched together preventing complete conversion for steric reasons. We report the synthesis of vinyl-functional highly branched silicone polymers based, at their core, on the ability to spatially locate functional vinyl groups along a silicone backbone at the desired frequency. Macromonomers were created and then polymerized using the Piers–Rubinsztajn reaction with dialkoxyvinylsilanes and telechelic HSi-silicones; molecular weights of the polymerized macromonomers were controlled by the ratio of the two reagents. The vinyl groups were subjected to iterative (two steps, one pot) hydrosilylation with alkoxysilane and Piers–Rubinsztajn reactions, leading to high molecular weight, highly branched silicones after one or two iterations. The vinyl-functional products can optionally be converted to phenyl/methyl-modified branched oils or elastomers.