(226ak) Solution Copolymerization of Ethylene and Propylene Catalyzed By [O-NS]TiCl3

The single-site catalytic system based on the metallocene complexes of group IV metals have been extensively studied. Recently, there has been a growing interest in developing new nonmetallocene catalysts, and in expanding beyond the first half of the transition metal series and various ligand backbones, as well as allowing access to previously inaccessible macromolecules. Of the successful nonmetallocene catalysts developed, the metal complexes possessing phenoxy-imine ligands are one of the promising examples. Group IV metal complexes [O^-NX^R]TiCl₃(O^-N=phenoxy-imine, X=O, S, Se, R=alkyl)proved to be an excellent catalyst for the olefin polymerization.

In the present work, the catalyst [O^-NS]TiCl₃ was used for ethylene and propylene copolymerization with the MAO as cocatalyst. The effects of copolymerization conditions such as polymerization temperature, cocatalyst concentration and feed ratio of ethylene/propylene (E/P) were investigated in toluene solution. The resulting copolymers were characterized by gel permeation chromatography(GPC), differential scanning calorimetry(DSC) and ¹³carbon nuclear magnetic resonance(¹³C-NMR) etc. The reactivity ratio and characteristics of the final copolymers were also discussed.

For this catalytic system, the activity of the given catalyst reaches 1.6×10⁶g Polymer/(mol Ti h atm) in the ethylene polymerization process, and it will reduce by 50% at most with the propylene insertion under similar conditions. Whereas, the catalytic system can’t catalyze the propylene polymerization. It has been found that polymerization behaviors were mainly dependent on [Al] to [Ti] ratios, temperatures and monomer feed ratios of E/P. Optimum [Al]:[Ti] ratio and  polymerization temperature for the highest yield of copolymer have been obtained. In particular, a series of E-P copolymers with M_n=10,000～40,000 was synthesized. Most E-P copolymer samples have polydispersity values close to a Schulz-Flory distribution(M_w/M_n≈2). Thermal behavior for these copolymers was studied by means of the DSC technique. It has been observed that T_m increases with increasing the ethylene content due to the crystallization of EEE block segments. However, with increasing the propylene content, two melting peaks appeared at 124^oC and 104^oC. ¹³C-NMR results showed that the copolymers are essentially composed of long ethylene sequences with some isolated PP diad units and less amount of isolated propylene units, as concluded from the low values of EPE triads for both samples and the higher values for PPE+EPP. The PPP triad is negligible for all samples. Also, The obtained monomer reactivity ratios(r_E=13.7-18.6, r_P=1.1-1.5) indicated a long ethylene sequences in the E-P copolymers.