Cationic polymerization of 1,3-pentadiene : IV. Initiation by aluminum chloride in an apolar solvent: effect of various electron donors

The polymerization of 1,3-pentadiene (PD) initiated by aluminum trichloride in nonpolar solvent was carried out in the presence of various electron donors (EDs) such as ethyl acetate, (EtOAc) tert-butyl acetate, dimethyl phthalate (DMP), N,N-dimethyl formamide, N,N-dimethyl acetamide and dimethyl sulfoxide. Addition of an ED whatever its nature to the polymerization medium, in a one-to-one molar ratio relatively to the Lewis acid, resulted in a decrease of the overall yield and an increased proportion of crosslinked polymer. The molecular weight distribution of the soluble fraction was narrower than that of polymerizations carried out without ED. The microstructure of the soluble polymers can be tuned using different EDs, showing that they are interacting with the active species. For instance EtOAc increased polymer isomerization while DMP increased polymer cyclization. Thus, the nature of the chemical functions borne by the ED does not seem to be the only parameter explaining its influence on the polyPD microstructure. If crosslinking efficiency seems to be roughly correlated to the donicity scale of the EDs, termination reaction is not. It was shown that the complexation between the Lewis acid and the EDs containing a carbonyl group involved the carbonyl oxygen atom. The decrease of polymerization yield when using the EDs was assigned to this complexation between the ED and AlCl₃.