Perfectly Alternating Ethylene/2-Butene Copolymers by Hydrogenation of Highly Stereoregular 1,4-Poly(1,3-diene)s: Synthesis and Characterization

In recent years it has been introduced a new generation of complexes of transition metals and lanthanides with various ligands containing donor atoms such as P, N, and 0 (e.g., phosphines, imines, iminopyridines, and ketoimines) that, in combination with MAO, give highly stereoregular polymers (cis-1,4, iso- and syndiotactic; 1,2, iso- and syndiotactic) from various substituted butadienes (i.e., isoprene, 1,3-pentadiene, 1,3-hexadiene, 3-methyl-1,3-pentadiene, 1,3-heptadiene, 1,3-octadiene, and 5-methyl-1,3-hexadiene). The availability of all these stereoregular polymers has allowed us to have access, via hydrogenation reaction with p-toluenesulfonyl hydrazide, to a whole series of olefin homopolymers and perfectly alternating copolymers which, in some cases, were not obtainable through the simple stereospecific polymerization of the corresponding monomers. In this communication, we report on the synthesis and characterization (by NMR, DSC, GPC, and X-ray) of four perfectly alternating ethylene/2-butene copolymers having different stereoregularity degree, from completely ethylene/2-butene copolymer obtained by isotactic to predominantly syndiotatctic; in particular, the racemo-di-isotactic hydrogenation of diisotactic trans-1,4-poly(2,4-hexadiene) is a novel polymer which was never reported before.