The characteristics of lanthanide coordination catalysts and the cis‐polydienes prepared therewith

The stereoregularity of polydienes is almost the same in regard to the individual elements of the lanthanide series, whereas the activity of the Ln catalysts in diene polymerization varies from one to the other within the series. The latter may be attributed to the difference in the number of electrons that occupy the 4f orbitals. It has been proved that the polymerization of dienes with Ln catalysts under certain conditions proceeds by a “living polymer” mechanism. With regard to the polymerization of butadiene, the most active catalyst is a Nd3+species a new binary system of NdCl3-3ROH + AlR3 has been discovered. The cis- 1,4 content in polybutadiene is about 97% and the 1,2 content, less than 1%. For the polymerization of isoprene with a Nd3+ catalyst system, the effects of ligand and alkyl groups in AIR3 on cis-1,4 content (ca. 95%) in polyisoprene can be neglected. For the copolymerization of butadiene and isoprene, the cis-1,4 contents of these two monomeric units in the copolymer are greater than 95% the reactivity ratios r1 and r2 are determined. and the Tg's of the copolymers of various compositions deviate slightly from the calculated values for random copolymers. A linear relationship exists between the yield strength from the stress-strain curve of Ln-polvbutadiene and its [n] This relationship is verified by Ln-polyisoprene and natural rubber but different slopes are obtained