✍ Scribed by Hiraki, Katsuma ;Inoue, Takeo ;Hirai, Hidefumi
No coin nor oath required. For personal study only.
ESR spectra of homogeneous catalyst derived from tris(acetylacetonato)titanium(III) and triethylaluminum were observed at several temperatures from −78°C, to +25°C, at molar ratios of aluminum to titanium of 1–108. At −78°C, this catalyst yields a violet complex which shows an ESR signal with a g value of 1.959 and is associated with the first intermediate. At −40°C to −30°C, this signal decreases, and two signals with g values of 1.947 and 1.960 are observed. The latter two signals diminish at −5°C to +10°C, while two kinds of new signals with g values of 1.965 and 1.969 appear overlapping each other. The structures of the species corresponding to these five signals are discussed on the basis of the ESR spectra, the intensity change, and the unpaired spin distribution. A new signal with a g value of 1.978 is found in the presence of butadiene at 25°C at Al/Ti > 8 and is assigned to a growing end of polybutadiene with this catalyst. The polymer yield increases remarkedly at Al/Ti molar ratios greater than 10. The microstructure of the resulting polymer consists almost completely of 1,2 units. The structure of the growing end is proposed to be a titanium (III) species containing two 1‐substituted allyl groups, by comparison with the structure ascribed to the growing end of polybutadiene with n‐butyl titanate‐triethylaluminum catalyst.
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## Abstract Polymerizations of butadiene, penta‐1,3‐diene, and isoprene with __n__‐butyl titanate–triethylaluminum catalyst are examined by ESR measurements on the polymerization state. At Al/Ti molar ratios greater than 2.9 where the conjugated dienes are polymerized, the polymerization system of