Abstract:
Electron donors are added to Ziegler-Natta catalyzed propylene polymerization to enhance the productivity and isotacticity of polymer products. The development of new electron donors becomes the key target in designing new generation catalysts for propylene polymerization. In this research, relationships between the activity/property and structures of 3 groups of electron donor were investigated by QSAR/QSPR approaches. All three QSAR models of phthalates, 1,3-diethers and malonates showed good predictive ability (R2≥0.93, R2CV≥0.84). However, the usage of obtained QSAR models is limited owing to the small size of the training set. This study founded that adsorption energies of electron donors to catalyst surface are linearly related to experimental activities. Hence, the QSPR for adsorption energies was performed for a set of 24 compounds from 3 different groups. The QSPR model shows high correlation (R2=0.84, R2CV = 0.83, R2predict = 0.77) between adsorption energies and three dominant descriptors Among three groups of electron donor, malonate compounds are the most potent. Finally, the roles of malonate donors were investigated by DFT calculations. Adsorption calculations of a malonate compound on the MgCl2 (110) surface revealed that the chelate mode was preferred over mono, bridge, and zip modes. From mechanistic study, we can conclude that the role of malonate donors is to give stereoselectivity which elucidated by the steric hindrance between the propylene and the malonate donor. In addition, we found that the malonate donor also stabilized the transition state structure by transferring electrons to Ti resulting in the reduction of the activation energy and hence the catalyst becomes more active. In conclusion, the results from QSPR model and mechanistic studied are in good agreement.
