Cyclopolymerization and copolymerization of functionalized 1,6-heptadienes catalyzed by Pd complexes: mechanism and application to physical-gel formation.

Cationic Pd complexes, prepared from [PdCl(ArN=C(12)H(6)=NAr)(Me)] and Na[B{3,5(CF(3))(2)C(6)H(3)}(4)] (NaBARF), catalyze the cyclopolymerization of 4,4-disubstituted 1,6-heptadienes. The polymers produced contain a trans-fused five-membered ring in each repeating unit. NMR spectroscopy and FAB mass spectrometry of the polymers formed indicated that the initiation end of the chain contains either the cyclopentyl group derived from the preformed Pd-monomer complex or a hydrogen atom left on the Pd center by the chain-transfer reaction. The stable cyclopentylpalladium species are involved in both initiation and propagation steps and undergo isomerization into (cyclopentylmethyl)palladium species followed by the insertion of a CH=CH(2) bond of a new monomer molecule into the Pd-CH(2) bond. Copolymerization of 1,6-heptadiene derivatives with ethylene, catalyzed by the Pd complexes, yields polymers that contain trans five-membered rings and branched oligoethylene units. Copolymerization of isopropylidene diallylmalonate with 1-hexene affords a polymer with 26% diene incorporation. The copolymerization consumes 1-hexene more readily than isopropylidene diallylmalonate, although gel permeation chromatography and NMR spectroscopy of the polymers produced show the formation of copolymers rather than of a mixture of homopolymers. Polymerization of 1-hexene initiated with a Pd-barbiturate complex and terminated with 5-allyl-5-hexylpyrimidine-2,4,6(1H,3H,5H)-trione/Et(3)SiH leads to polyhexene with barbiturate moieties at both terminal ends. Addition of 5-hexyl-2,4,6-triaminopyrimidine to a toluene solution of the telechelic poly(1-hexene) converts the solution into gel.