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

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 (M n ) 5 1180 Da, PDI 5 1.32 for PMSO, M n 5 1720 Da, PDI 5 2.17 for PMSO that was heated for 1000 h at 130 8C]. PDI correlated best with the z-average MW. The M n was the best predictor of the viscosity. For samples with close M n , the higher PDI corresponded to a higher viscosity index. V C 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46150.