Biosourced Janus Molecules as Silica Coupling Agents in Elastomer Composites for Tires with Lower Environmental Impact

A biosourced Janus molecule was used as a coupling agent between silica and unsaturated polymer chains in an elastomeric composite suitable for tire compounds with low energy dissipation, with potential important reduction of the environmental impact of the tire. 2-(2,5-Dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (serinol pyrrole, SP) was synthesized through the neat reaction of serinol and 2,5hexanedione, with a high atom efficiency (ca. 85%). Adducts of SP with silica were prepared (SP approximate to 9% by mass), with very high yield. In the whole process, from reagents to adducts, only substances from natural sources could be used, and the only co-product was water and the carbon efficiency was close to 100%. The silica/SP adduct was used in an elastomeric composite based on diene elastomers such as poly(styrene-co-butadiene) and poly(1,4-cis-isoprene) from Hevea brasiliensis. Comparison was made with a composite containing silica and a traditional coupling agent, a sulfur-based silane, bis(triethoxysilylpropyl)tetrasulfide (TESPT). SP appears to behave as a coupling agent for silica. To have similar properties for the SP and TESPT-based composites, tuning of the formulation of the composite with silica/SP has to be performed. Model reactions revealed the condensation of the OH of SP with the SiOR groups of an alkoxysilane, the reaction of the pyrrole ring with sulfur and a thiyl radical and the reaction of the sulfurated pyrrole ring with the unsaturation of squalene. SP appears thus able to establish covalent bonds with both silica and the unsaturated elastomer. With SP, the release of ethanol, which occurs from the silanization of silica with TESPT and is usually burned in industrial plants to give CO2, is avoided. This work paves the way for the development at the industrial scale of elastomeric composites which allow remarkable reduction of the carbon footprint of the tire technology.