(643b) Enhancement on Alternating Copolymerization of Ethylene and Carbon Monoxide By Nickel-Based Catalyst

Polyketone (PK) is an alternating copolymer of olefins and carbon monoxide. The copolymer has attracted wide attention because it is directly based on inexpensive olefins and carbon monoxide as monomers and has excellent properties as engineering plastics. However, the commercialized PK¹ is produced using Pd-based catalysts containing a bidentate phosphine ligand structure, which accounts for the largest part of the production cost. A few of studies^2-5 have begun to look for non-noble metal catalysts, such as Nickel-based complex. However, the activity of these catalysts is still unsatisfactory. Additionally, both the production systems of the Pd-based catalysts and Nickel-based catalysts adopt slurry polymerization, which will bring severe problems such as the formation of PK with low bulk density and reactor fouling. Nevertheless, the PK is difficult to be produced by homogeneous solvent polymerization because of its low solubility in common solvents and its high melting point (∼240 ℃) caused by the interchain dipolar interaction between carbonyl groups.

Herein, the Nickel-based complex², [Ni(2-tol)(PPh₃)(N,O)], was used as the catalyst for the slurry polymerization process. Effects of the co-catalyst, the aging process in carbon monoxide and the solvent type on the catalytic reactivity and the molecular weight of copolymer were investigated. When Ni(COD)₂ was employed as the co-catalyst, the activity and molecular weight of PK were both increased. The aging of the co-catalyst system in carbon monoxide atmosphere would result in the decreases of activity and the molecular weight of PK while the single catalyst system was not affected by the aging process in carbon monoxide up to the span of one hour. This suggested that the catalytic mechanism of the system containing co-catalyst were different from that of the single catalyst system. Using dichloromethane as the solvent could greatly increase the activity and the molecular weight of the PK. The activity was increased by 355% compared to that of the toluene solvent system, and the molecular weight was increased sharply from 330 kDa to 1510 kDa.

For the first time, the homogeneous solvent polymerization for PK production was successfully carried out with the highest productivity. With a mixture of dichloromethane and hexafluoroisopropanol (HFIP) as the solvent, the highest productivity efficiency of 6.1×10⁴ g Pk /mol Ni was obtained when the ratio of carbon monoxide to ethylene concentration was 8:1. As the concentration of carbon monoxide concentration decreased, more copolymers were formed, and the molecular weight of PK was increased to 560 kDa. Different from the previous work with the same main catalyst³, it was proved that there was no induction period for this Nickel-based catalyst.

1. [1] http://www.hyosungchemical.com/cn/business/pok.do.
2. [2] W. Kläui, J. Bongards, G. J. Reiß, Angew. Chem., 2000, 112,4077–4079.
3. [3] B. Udo, E. Eva, R. Anna, S. Rafaël, K. Wolfgang, J. Catal., 2011, 283,143-148.
4. [4] B. Udo, H. Gerhard, F. Walter, J. Organomet. Chem., 2012, 720, 73-80.
5. [5] X. F. Jia, M. Zhang, M. Li, F. Pan, K. Ding, L. Jia,et al, Organomet., 2017, 36, 1122−1132.