Molecular Simulation On The Interaction Mechanism Of The Sulfonimide Internal Electron Donor Over Ziegler-Natta Catalyst System Based On Titanium For Propylene Polymerization

Ziegler-Natta titanium polypropylene catalyst is a widely used catalyst in industrial application.After the research and development of several generations of catalyst,the current research of this catalyst is focusing on the development of new electron donors.In this work,the most optimal conformations of Di-n-butyl phthalate(DNBP),9.9-Bis(Methoxymethyl)-Fluorene(BMMF)and N-(2,6-Diisopropylphenyl)bis-trifluoromethanesul fonimide(NPPFS),N-(3-chlorophenyl)bis-trifluoromethanesulfonimide(NCPFS),N-phenyl-bis-trifluoromethanesulfonimide(NPFS),1-[bis(trifluoromethanesulfonyl)methyl]-2,3,4,5,6-pe ntafluorobenzen(NFPFS)were screened by molecular simulation.The adsorption types of NCPFS on the MgCl2,surface model,and the first step and second step of propylene molecules coordination and insertion on the adsorption models were explored.The influence of NCPFS on propylene polymerization process in activity and isotacticity was also studied.(1)Based on the TINKER,the optimal conformation of DNBP,BMMF,NPPFS,NCPFS.NPFS.and NFPFS were compared,and obtained to build the adsorption model of the electron donor on the MgCl2 surface model ACT.(2)In the absence of electron donor,the activity center of the ACT model only indicated regional selectivity in the insertion of the first propylene molecule without stereoselectivity.The activity center of ACT model was isotactic when the second propylene molecule insertion.(3)The conformation with the lowest energy of NCPFS adsorpted on the surface of MgCl2(110)crystal plane with the types of monodentate(O on Mgl,Mg2,Mg3),chelate(O on Mg2),and the bridge(O on Mg1,Mg2 and Mg2,Mg3),were studied,respectively.The monodentate adsorption of NCPFS on Mgl site was the most stable,followed by the chelate adsorption of NCPFS on Mg2 site.(4)In the nine co-adsorption models of NCPFS.energy of the first step of propylene coordination significantly increased,indicating that the existence of the electron donor increased the steric hindrance of the active center model significantly.The insertion energy barriers of NCPFS-a and NCPFS-c model with four insertion types reduced in large scale compared to ACT,so these two models which are monodentate adsorption of the NCPFS on the nearest Mg1 site helped to improve the activity of the catalyst.NCPFS-b model did not favour the generation and growth of polypropylene chain because of the strong interaction between Ti atom and O atom.The other six adsorption models showed small differences in the insertion energy barriers with that of the ACT active center,and the regional selectivity of the models stayed still.(5)Similarly,for the second step of propylene coordinated on the nine NCPFS adsorption models,the energy increased significantly,indicating that the existence of electronic donors increased the steric hindrance of the active center model.The monodentate adsorption models NCPFS-d,NCPFS-e and NCPFS-f on Mg2 and Mg3 which are far from the Ti active center were syndiotactic active centers,and the rest are isostatic ones.Monodentate adsorption models NCPFS-a-1s,NCPFS-a-lr of which the NCPFS adsorpted on the nearest Mg1 site,and bridge adsorption models NCPFS-h-1s,NCPFS-h-1r,NCPFS-i-1s,and NCPFS-i-lr improved the activity of catalyst largely.Besides,NCPFS-a performed outstandingly with the remarkable improvement of stereoselectivity,and it was the most stable model.