Copolymerization of 1,3‐dienes with CpTiCl₃‐MAO. Some cases in which the mode of monomer coordination affects the copolymer structure

The following pairs of monomers were copolymerized using the catalyst system CpTiCl 3 /methylaluminoxane (MAO): 1,3‐butadiene/( E )‐1,3‐pentadiene, 1,3‐butadiene/4‐methyl‐1,3‐pentadiene and 4‐methyl‐1,3‐pentadiene/( Z )‐1,3‐pentadiene. The copolymers were characterized by NMR and infrared examination. 4‐Methyl‐1,3‐pentadiene/( Z )‐1,3‐pentadiene and 1,3‐butadiene/( E )‐1,3‐pentadiene gave copolymers having a composition intermediate between that of an ideal and that of an alternating copolymer. 1,3‐Butadiene/4‐methyl‐1,3‐pentadiene gave block copolymers only. These results have been interpreted on the basis of a different mode of coordination of the monomers. The cis ‐η 4 coordination is by far the most stable for 1,3‐butadiene and ( E )‐1,3‐pentadiene, while for ( Z )‐1,3‐pentadiene and 4‐methyl‐1,3‐pentadiene there is probably an equilibrium between the cis ‐η 4 and trans ‐η 2 form. Both these forms are reactive in the case of ( Z )‐1,3‐pentadiene, while only the trans ‐η 2 form is so in the case of 4‐methyl‐1,3‐pentadiene.