Urushiol-derived non-silane coupling agent

Sulfur was chemically incorporated into urushiol in one step to afford an oligomeric sulfurized urushiol (SU). About 53% of the linkages between urushiol monomer units are cleavable multi-sulfidic bonds. Surface modification of silica with SU can be achieved either in a suspension before rubber compounding or in situ during rubber compounding. SU performs better when added in situ into the rubber compound than when used to pre-modify silica. Mooney viscosity and Payne effect studies of the uncured rubber compounds show that SU is as effective as TESPT to promote filler dispersion during mixing. The increased bound rubber content and suppressed filler flocculation demonstrate that SU does indeed generate covalent filler-rubber interactions during mixing in contrast to our previously reported hydrogenated urushiol, which only act as a covering agent. However, SU is less effective than TESPT as a coupling agent. The dynamic mechanical properties of the SU-containing vulcanizate are intermediate between the TESPT-containing standard and the hydrogenated urushiol-containing standard. When SU is used to replace 50% TESPT, mechanical and dynamic mechanical properties of the two vulcanizates are essentially identical. Noteworthy is that the reaction between SU and silica during rubber compounding produces water instead of ethanol, which the reaction of silica and TESPT produces, as a volatile organic compound.