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Bulky bis(phenolate) complexes of titanium alcoholates were found to initiate living polymerization of ε-caprolactone, affording a polyester with a narrow molecular weight distribution. By changing the initial monomer-to-initiator mole ratio, the molecular weight of the polymer was controlled over a wide range. 1 H NMR studies on the produced polymer showed the presence of an alkoxy group originating from the initiator at the polymer terminal, indicating that the polymerization takes place at the titanium alcoholate bond of the initiator. Use of titanium complexes prepared with nonbridged hindered phenols or a less bulky bisphenol resulted in a poorly controlled chain growth or no polymerization.
Takeuchi et al. (Sat,) studied this question.