The polymerization of 1,3-pentadiene initiated by AlCl3 was investigated in a nonpolar medium at room temperature. It was shown that, besides propagation, the system undergoes various side reactions such as cross-linking, cyclization, double bond isomerization, .... An examination of the various possible structures of the polymer showed that the comparison of the 1 H and 13 C quantitative NMR spectroscopies allows the determination of the relative importance of cyclization and double bond isomerization. It is shown that some of these side reactions can be kept under control: for instance crosslinking could be avoided at low monomer concentration, while cyclization could be strongly decreased at high monomer concentration and by catalyst sublimation. Double bond isomerization was eliminated in the presence of a transfer agent such as methyl-2-butene-2.

SUMMARY The cationic polymerization of 1,3-pentadiene initiated with aluminium chloride was studied in a non-polar solvent. Experiments carried out in the presence of 2,6-di-tert-butylpyridine (DtBP) clearly demonstrated that the major initiation process is the direct initiation mechanism, even though the existence of a cocatalytic mechanism to small extent cannot be rejected. This result is also evidenced by the linear dependence of the conversion on A1C13 concentration, and by experiments carried out in the presence of hydrogen chloride showing the independence of the polymerization yield on the hydrogen chloride concentration.

The cationic polymerization of 1,3‐pentadiene initiated with aluminium chloride was studied in a non‐polar solvent. Experiments carried out in the presence of 2,6‐di‐tert‐butylpyridine (DtBP) clearly demonstrated that the major initiation process is the direct initiation mechanism, even though the existence of a cocatalytic mechanism to small extent cannot be rejected. This result is also evidenced by the linear dependence of the conversion on AlCl3 concentration, and by experiments carried out in the presence of hydrogen chloride showing the independence of the polymerization yield on the hydrogen chloride concentration.

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