Coordinative chain transfer polymerization of 1-decene in the presence of a Ti-based diamine bis(phenolate) catalyst: a sustainable approach to produce low viscosity PAOs

A Ti-based diamine bis(phenolate) catalyst, [Ti{2,2′-(OC6H2-4,6-tBu2)2NHMePhMeNH}Cl2], was synthesized and fully characterized by elemental analysis and NMR spectroscopy. Very effective, fast, and reversible chain transfer was achieved between an active transition metal-based propagating center and diethylzinc, which acted as a chain transfer agent, in the coordinative chain transfer polymerization (CCTP) of 1-decene. The molecular weight of the obtained oligomers was efficiently regulated and decreased by the addition of ZnEt2 to the oligomerization system. The kinetic results disclosed that ZnEt2, besides its primary role as a chain transfer agent, also significantly reduced the catalyst consumption. DFT calculations were performed to reveal the reaction mechanism. Notably, the CCTP technique led to the occurrence of fast and reversible chain transfer, bypassing the β-H termination pathway, so oligomer chains without any unsaturated bonds were obtained. Finally, a linear relationship between the ZnEt2 content and the tacticity characteristic of the resulting oligomers was detected. The viscosity results showed that the obtained oligomers had a viscosity index in the range of 131.7–159.7 and pour point values less than −48 °C, which were comparable with the properties of commercial polyalfaolefin-based oils. Our proposed green approach for producing low viscosity polyalphaolefins (PAO4 and PAO6) can replace the industrially-used and hazardous BF3 catalyst system with great success.