Heat- and light-induced thiol-ene oligomerization of soybean oil-based polymercaptan

Authors: Bantchev, Grigor; Vermillion, Karl; LANSING, JAMES - Orise Fellow; Biresaw, Girma

Submitted to: Journal of Applied Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2017
Publication Date: 5/5/2018
Citation: Bantchev, G.B., Vermillion, K., Lansing, J.C., Biresaw, G. 2018. Heat- and light-induced thiol-ene oligomerization of soybean oil-based polymercaptan. Journal of Applied Polymer Science. 135(17). https://doi.org/10.1002/app.46150.
DOI: https://doi.org/10.1002/app.46150

Interpretive Summary: This research evaluated the heat- and light-induced changes in the structure and properties of polymercatanized soybean oil (PMSO). PMSO is a novel bio-based material that is tested as a lubricant additive and polyurethane precursor. There are no previous reports on the changes that occur in this material upon storage. In addition, the heat-induced changes can lead to properties more desirable for some applications. In the current study, researchers from ARS, Peoria, IL, showed that PMSO forms sulfide-bridged oligomers, leading to a material with higher viscosity. Formulas to predict the viscosity from the molecular weight of the new materials were described. A previously unreported correlation between the polydispersity of the oligomers and the viscosity index (VI, it shows how much viscosity changes with temperature) was observed. If confirmed for a wider class of oligomers, it can be used as a guide for preparation of lubricants with better VI.

Technical Abstract: Polymercaptanized soybean oil (PMSO), the product of a thiol-ene reaction between soybean oil and hydrogen sulfide, is a material of interest as a lubricant additive and polymer precursor. We investigated with gel permeation chromatography, nuclear magnetic resonance (one-dimensional and two-dimensional), gas chromatography-mass spectrometry, and viscometry the changes that occur with PMSO upon heating or ultraviolet irradiation. The observed changes were due to a further thiol-ene reaction between the thiol groups and the residual unsaturation. The formation of oligomers was a result of new sulfide bridges. Additionally, tetrahydrothiophene moieties were detected. An almost linear increase of the average molecular weight (MW) and the polydispersity index (PDI) was observed upon heat treatment [number-average MW (Mn) = 1180 Da, PDI = 1.32 for PMSO, Mn = 1720 Da, PDI = 2.17 for PMSO that was heated for 1000 h at 130 °C]. PDI correlated best with the z-average MW. The Mn was the best predictor of the viscosity. For samples with close Mn, the higher PDI corresponded to a higher viscosity index.