Abstract
AbstractMAO/CpTiCl3 is an active catalyst for the polymerization of various types of 1,3‐dienes. Butadiene, (E) ‐ and (Z) −1,3‐pentadiene, (E) −2‐methyl‐1,3‐pentadiene and 2,3‐dimethylbutadiene yield, at room temperature, polymers with a cis‐1,4 or a mixed cis/1,2 structure. 4‐Methyl‐1,3‐pentadiene and (E,E) −2,4‐hexadiene give, respectively, a 1,2 syndiotactic and a trans‐1,4/1,2 polymer. MAO/CpTiCl2·2THF and MAO/(CpTiCl2)n are less active than the CpTiCl3 catalyst, but give the same type of polymers. A change of stereospecificity with temperature was observed in the polymerization of (Z)‐1,3‐pentadiene: a cis‐1,4 isotactic polymer was obtained at +20°C, and a crystalline 1,2 syndiotactic polymer at −20°C. This effect was attributed to a different mode of coordination of the monomer, which is cis‐η4 at +20°C and may be trans‐η2 at −20°C. Results obtained with catalysts from CpTi(OBu)3 and Ti(OBu)4 are reported for comparison. An interpretation is given of the formation of cis‐1,4 isotactic poly(2‐methylpentadiene) and of 1,2 syndiotactic poly(4‐methylpentadiene), as well as of syndiotactic polystyrene.
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