Controlled isomerization polymerization of olefins, cycloolefins, and dienes

This article features recent studies on Pd-catalyzed isomerization polymerization of dienes, cyclopentenes and alkenylcyclohexanes. Pd complexes with diimine ligands promote controlled cyclopolymerization of functionalized 1,6-dienes to afford the polymers with repeating trans-1,2-bis(methylene)cyclopentylene units. The dienes copolymerize with various olefins, such as ethylene, α-olefin, and cyclopentene, to yield the polymers containing the trans–fused five membered rings.

The polymerization of 7-alkyl-1,6-dienes by the Pd catalysts involves stereoselective cyclization as well as chain-walking, and the produced polymers contain 1,2-trans-cyclopentylene units separated by oligomethylene spacer along the polymer chain. Trienes with 1,6-diene moieties undergo double cyclizative isomerization polymerization to give the polymers with two cyclopentylene units connected directly or by oligomethylene spacer.

The density and distribution of the cyclopentylene units in the polymer can be accurately controlled by changing the monomer. Polymerization of 4-alkylcyclopentenes by the Pd complex, produces the polymers composed of 1,3-trans-cyclopentylene units and oligomethylene spacer.

The Pd complexes with pseudo-C2 symmetrical structure bring about isospecific polymerization of the cyclopentenes. The isotactic polymers of 4-alkylcyclopentene show liquid crystalline properties. Isomerization polymerization of alkenylcyclohexanes by the Pd catalysts leads to the polymers with high melting point caused by regulated alignment of 1,4-trans-cyclohexylene units. Homopolymerization of methylenecyclohexanes also proceeds smoothly in the presence of the Pd catalyst in spite of general low reactivity of the 1,1-disubstituted olefins.

This article originally appeared in Polymer 82,  2016, Pages 392-405