Hydrogenation Kinetics Study: Precise Control of C=C Bonds in Polyisoprene (PI)-Containing Block Copolymers via Diimide Hydrogenation

High Resolution Image Download MS PowerPoint Slide Polydienes containing a C=C bond in each unit, such as polybutadiene (PBD)- or polyisoprene (PI)-containing polymers, have served as an important backbone of polymer applications in our daily lives. For versatile use of polydienes in various applications, C=C bonds in polydienes can be hydrogenated to achieve a desirable saturation level and/or additionally modified to obtain suitable structure–property sets. Among different hydrogenation procedures, non-catalytic, diimide hydrogenation using p -toluenesulfonyl hydrazide (TSH) can enable easier and precise control of hydrogenation level in C=C bonds at mild conditions. Here, for the first time, we reported a systematic hydrogenation kinetics study of one representative PI-containing polymer, i.e., polystyrene- b -polyisoprene- b -polystyrene (SIS) triblock copolymer with high molecular weight via TSH-based, diimide hydrogenation using NMR, SEC, and thermal analyses. We evaluated hydrogenation level (HL = 0∼99.9%) vs reaction time (0∼24 h) of SIS polymer and compared our kinetics results with other PBD- or PI-containing polymers with different chain architectures, compositions, and hydrogenation conditions to develop a universal efficacy of this diimide hydrogenation method and build a comprehensive understanding among these reports. We achieved HL = 51% in 1 h and HL > 99.9% by 24 h. Our analyses confirm that no side reactions occur up to 48 h without affecting other copolymer blocks. Our kinetics data align well with other similar polydienes but cover a wider range of reaction times (up to 48 h) than those in the literature. Using this information, a target hydrogenation level can be precisely achieved by controlling reaction time under mild conditions. Overall, this TSH-based diimide hydrogenation method is universal and effective over a broad range of PBD- and PI-containing polymers with different chain architectures and compositions.