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

Abstract

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 O (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, 1,3pentadiene, 1,3-hexadiene, 3-methyl-1,3-pentadiene, 1,3-heptadiene, 1,3octadiene, 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 isotactic to predominantly syndiotatctic; in particular, the racemo-di-isotactic ethylene/2-butene copolymer obtained by hydrogenation of diisotactic trans-1,4-poly(2,4-hexadiene) is a novel polymer which was never reported before.

Dienes Polymerization: Where We Are and What Lies Ahead

“…The strategies adopted to modify the selectivity during the polymerization runs are of different types, ranging from adding a specific ligand to changing the cocatalyst (i.e., different type of aluminum alkyl) and from increasing the Al/Mt molar ratio to modifying the polymerization temperature. 229−231 isotactic cis-1,4-poly(3-methyl-1,3-pentadiene) 249,250 ethylene-alt-2-butene copolymer 260 (E)-3-methyl-1,3-pentadiene CoCl 2 (P t Bu 2 Me) 2 /MAO 149 syndiotactic cis-1,4-poly(3-methyl-1,3-pentadiene) 46,47 ethylene-alt-2-butene copolymer 260 (E)-3-methyl-1,3-pentadiene CoCl 2 (PEtPh 2 ) 2 /MAO 151 isotactic (E)-1,2-poly(3-methyl-1,3-pentadiene) 251−253 isotactic poly(3-methyl-1-pentene) 261,262 (E)-3-methyl-1,3-pentadiene FeCl 2 (Bipy) 2 /MAO 99−101 syndiotactic (E)-1,2-poly(3-methyl-1,3pentadiene) 104,105 syndiotactic poly(3-methyl-1-pentene) 192 2,3-dimethyl-1,3-butadiene CpTiCl 3 /MAO 54 cis-1,4-poly(2,3-dimethyl-1,3-butadiene) 107 ethylene-alt-2-butene copolymer 260 FeCl 2 (Bipy) 2 /MAO 99−101 4-methyl-1,3-pentadiene CpTiCl 3 /MAO 48,50 syndiotactic 1,2-poly(4-methyl-1,3-pentadiene) 254 syndiotactic poly(4-methyl-1-pentene) 192 (E)-1,3-hexadiene NdCl 3 (L)/TIBAO Butadiene is first polymerized with a catalytic system obtained by combining a cobalt complex with ligands (L1) (e.g., P t Bu 3 and P t Bu 2 Me), characterized by a cis-type selectivity, with formation of an amorphous cis-1,4-polybutadiene block; subsequently, a second ligand L2 is introduced (generally an aromatic phosphine of the type PRPh 2 , in which R = alkyl or cycloalkyl group) which replaces L1 on the cobalt atom, causing a drastic change of the catalytic selectivity, from cis-1,4 to syndiotactic 1,2, with the formation of a second block of crystalline polybutadiene with a 1,2 syndiotactic structure (the syndiotacticity degree and therefore the crystallinity vary according to the nature of the R group on the phosphorus atom).…”

“…As reported in detail in the previous paragraphs, the stereospecific polymerization of conjugated dienes is able to provide polymers having different stereoregularities depending on the nature of the monomer and the catalytic structure. ,,,,,,,,,,,,,− The availability of such a large numbers of highly stereoregular polidienes allowed to have access, through hydrogenation, to a whole series of highly stereoregular olefin homo- and copolymers, ,− in some cases difficult to obtain through the simple homo- or copolymerization of the corresponding monomers. In Figures and , and in Table , many examples of polyolefins obtained by hydrogenation of stereoregular polydienes are reported.…”

“…Perfectly alternating ethylene/α-olefin copolymers by hydrogenation of stereoregular 1,4-poly­(1,3-diene)­s. ,, …”

Isotactic and Syndiotactic Alternating Ethylene/Propylene Copolymers Obtained Through Non-Catalytic Hydrogenation of Highly Stereoregular cis-1,4 Poly(1,3-diene)s

“…We decided to examine the hydrogenation of these highly stereoregular poly(1,3-diene)s since, at least in principle, it could allow one to get through the hydrogenation process: ( i ) highly stereoregular iso- and syndiotactic poly(α-olefin)s from highly stereoregular 1,2 and 3,4 poly(1,3-diene)s ( Scheme 1 ); and ( ii ) perfectly alternating ethylene/α-olefin copolymers from highly stereoregular cis -1,4 and trans -1,4, iso- and syndiotactic, poly(1,3-diene)s ( Scheme 2 ), which in some cases are unlikely to the obtainable through the simple stereospecific homo- and co-polymerization of the corresponding monomers. We have recently reported the synthesis and characterization of: ( i ) isotactic poly(( R , S )-3-methyl-1-pentene) obtained by hydrogenation of isotactic 1,2 poly(( E )-3-methyl-1,3-pentadiene) [ 29 , 30 ], and ( ii ) ethylene/2-butene copolymers obtained by hydrogenation of some cis -1,4 and trans -1,4 highly stereoregular poly(1,3-diene)s [ 31 ].…”

Synthesis and Structure of Syndiotactic Poly(3-methyl-1-butene): A Case of 3/1 Helical Conformation for Syndiotactic Polymers

“…The synthesis of stereoregular poly­(1,3-diene)­s with controlled molecular structure has been recently improved thanks to the development of a new generation of catalysts based on complexes of transition metals and lanthanides with various ligands (e.g., phosphines, imines, imino-pyridines, and cheto-imines) in combination with MAO . These catalysts have demonstrated to be active and highly stereospecific, giving stereoregular poly­(1,3-diene)­s ( cis -1,4-isotactic and syndiotactic, 1,2-isotactic and syndiotactic) from various dienes (such as isoprene, 1,3-pentadiene, 1,3-hexadiene, 3-methyl-1,3-pentadiene, 1,3-heptadiene, 1,3-octadiene, and 5-methyl-1,3-hexadiene). − From all these stereoregular poly­(1,3-diene)­s, a whole series of stereoregular poly­(olefin)­s and perfectly alternating copolymers of olefins − have been obtained via the hydrogenation reaction. − Some of these new polymers cannot be obtained by simple stereospecific polymerization of the corresponding monomers. In particular, in this paper the preparation of syndiotactic poly­(3-methyl-1-butene) (sP3MB) by hydrogenation of syndiotactic 3,4-poly­(isoprene) is presented.…”