Effect of Ligand Steric Hindrance on Catalytic Polymerization of Cycloolefin Polymer (COP)

Abstract

The traditional two‐component Ziegler‐Natta catalyst has low catalytic activity when initiating ring‐opening metathesis polymerization (ROMP) and is unstable and easy to generate polymerization gels. Therefore, it is necessary to add a third group of ligands with appropriate steric hindrance to improve the catalytic activity of the catalyst. The effects of ligands′ steric hindrance and other reaction conditions on the catalytic activity of tungsten hexachloride (WCl6) as catalyst and aluminum triethyl (AlEt3) as co‐catalyst were investigated. The results showed that the size of the ligands′ steric hindrance affected the catalytic activity of ROMP, and the small steric hindrance caused the polymerization rate to be too fast, which was easy to produce gels, and when the steric hindrance of the ligands was too large, its solubility was not good, which was not conducive to the normal polymerization. When stearyl alcohol was selected as the ligand, the highest catalytic activity was 3123 mol cycloolefin polymer (COP)/mol W, and the reaction speed of polymerization was also the fastest and the complete transformation only needed 30 min when the ligand/W was 25. It was found that the polymerization reaction was stable without gels and the obtained polymer molecular weight was appropriate, 17.8 kDa, under the conditions of Al/W=80, reaction temperature 60 °C, monomer concentration 10 w/v %, catalyst/monomer 5*10−4 : 1, chain transfer agent/monomer 0.005 : 1.