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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 33, Number 12
BKCSDE 33(12)
December 20, 2012 

Butadiene Polymerization Catalyzed by Tri(aryloxo)aluminum Adduct of Cobalt Acetate
Ji Hae Park, Ahreum Kim, Sung Hae Jun, Gwanghoon Kwag, Ka Hyun Park, Junseong Lee, Bun Yeoul Lee*
Butadiene polymerization, trans-1,4-Polybutadiene, Cobalt complexes, Phenoxoaluminum complexes
Tris(2-phenylphenoxo)aluminum ((2-PhC6H4O)3Al) exists as a dimeric form in toluene. When toluene-insoluble anhydrous cobalt acetate is treated with tris(2-phenylphenoxo)aluminum in toluene, the toluene-soluble adduct (2-PhC6H4O)3Al·Co(OAc)2 is formed. The 2-phenylphenoxo ligand in the adduct can be replaced with another aryloxo ligand to give (aryloxo)(2-PhC6H4O)2Al·Co(OAc)2 (aryloxo = 2-methylphenoxo, 2-isopropylphenoxo, 4-methylphenoxo, 4-isopropylphenoxo, or 4-tert-butylphenoxo). These complexes are active for butadiene polymerization without gel formation when activated with an equivalent amount of (2-PhC6H4O)AlEt2 for 2 h. The highest activity, 175 kg/mol-Co (turnover number, 3200) was achieved with (2-PhC6H4O)3Al·Co(OAc)2 at 65 oC for 2 h. The microstructure of the polymer chains is mostly trans-1,4-configuration (70-75%) with the remaining being 1,2-vinyl. The cis-1,4-configuration observed by IR is minimal (1-5%). By replacing the 2- phenylpheoxo with a 4-alkylphenoxo ligand, the amount of 1,4-configuration slightly increases, resulting in increase in the endothermic melting signal at −30~50 oC in the DSC curve. The molecular weights of the polymers are high (Mn: 300000~800000) with a fairly narrow molecular weight distribution (Mw/Mn, 2.0-2.7).
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