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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 28, Number 12
BKCSDE 28(12)
December 20, 2007 

Efficient Bimodal Ring-opening Polymerization of ε-Caprolactone Catalyzed
by Titanium Complexes with N-Alkoxy-β-ketoiminate Ligands
Min Ho Cho, Jin San Yoon, Ik-Mo Lee*
N-Alkoxy-β-ketoiminate, Titanium complexes, ε-Caprolactone, Ring-opening polymerization, Transesterification
A series of titanium complexes containing terdentate β-ketoiminate ligands were found to be efficient for the ring-opening polymerization of ε-caprolactone (ε-CL), producing poly(ε-caprolactone) (PCL) with bimodal distribution. Steric factors imposed by methyl substituents on the back bone of the alkoxy group affected significantly the polymerization rate and physical properties of the resulting PCL. Intra- and intermolecular transesterifications rather than disproportional rearrangements were responsible for the bimodal behavior and for the change in the molecular weight (Mw). Dilution with toluene reduced yield, and lowered polydispersity (PDI) and Mw of PCL, while the catalytic activities of the dimeric complex, [Ti(Oi-Pr)2(N-alkoxy-β- ketoiminate)]2 and Ti(Oi-Pr)4 were not sensitive to the added solvent. The dimeric complex showed living character, while other catalysts suffered from chain termination reactions.
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