Formation of SBS triblock copolymers using waste soybean oil as coupling agent

Abstract

AbstractTriglyceride in the waste soybean oil (WSO) was used as coupling agent to synthesize a linear styrene‐butadiene‐styrene (SBS) triblock copolymer. The reaction occurred via a living anionic polymerization of styrene‐butadiene block copolymer (SB) using n‐butyllithium as initiator and cyclohexane as solvent and followed by the coupling reaction with the added WSO. Gel permeation chromatography (GPC) showed that for all SB‐Li precursors except the one with the Mn of 1000 g/mol, the resultant products consisted of two different sizes, one with the nearly comparable size with the precursor, the other with a Mn two‐fold higher than the precursor. On the other hand, the reaction of the SB‐Li precursor with the Mn of 1000 g/mol and the WSO only resulted in forming the molecule with a Mn two‐fold higher than the precursor. The results from the GPC and spectral analysis supported that upon the nucleophilic attack the ester group of the triglyceride in the WSO was broken, giving the SB‐C(O)‐fatty acid susceptible to the second the nucleophilic attack, thus forming the coupled product. The size of the SB‐Li precursor, the SB‐Li : WSO molar ratio, the S:B weight ratio and the coupling time were found to influence on the coupling efficiency. However, the size of the SB‐Li precursor showed highest impact on the coupling efficiency at which the larger the SB‐Li precursor, the lower the coupling efficiency. Regardless of the low coupling efficiency of the WSO, the WSO was found to be a potential coupling agent for the formation of the linear triblock copolymer. This was because the SBS triblock copolymer containing high SB diblock copolymers and prepared by the WSO showed slightly higher tensile strength than the one with less SB diblock copolymers prepared by a traditional coupling agent. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40684.