Study of solvent effect on the dissolution, size, structure and catalytic hydrogenation of nitrile butadiene rubber

Nitrile butadiene rubber (NBR) is an important synthetic rubber made by copolymerization of butadiene and acrylonitrile. The hydrogenated nitrile rubber (HNBR), made by selective hydrogenation of NBR, not only maintains the original oil resistance and wear resistance, but also greatly improves its weather resistance and ozone resistance properties, which is widely used in weapon parts, aerospace seals and other fields. It is a key hot topic for the chemical modification of unsaturated polymers. In this paper, we systematically investigated the influence of solvent properties on the dissolution behavior, size distribution molecular structure of NBR and catalytic performance in solvent by using nanometer particle size analyzer, ubbelohde viscometer and Fourier transform infrared spectroscopy combined with density functional theory (DFT). The results show that strong electrophilic solvents cannot dissolve NBR, but electron donating solvents and some weak electrophilic solvents can dissolve NBR well. Especially in ketone solvents, NBR has small particle size with narrow distribution. DFT calculations reveal that compared with the gas atmosphere, the bond lengths of C=C double bonds in NBR segment has increased in all solvents, and show an increasing trend as the polarity of the solvent increases. The dipole moment of NBR also increases with the increase of solvent polarity. Especially in ketone solvents, the highest occupied molecular orbital (HOMO) of NBR molecule moves from the edge to the inside of the molecule under the strong solvent effect, indicating that it may have a positive influence on the C=C double bond inside the chain segment. The hydrogenation results show that the hydrogenation activity of NBR in the electron donating solvents is higher than that in weak electrophilic solvents, but no matter which solvent is selected, the hydrogenation selectivity to C=C double bonds of NBR is 100%. This study provides a theoretical basis for the selection of solvents in the NBR heterogeneous solution hydrogenation system. © 2021, Editorial Board of CIESC Journal. All right reserved.