Cationic polymerization of 1,3-pentadiene initiated with aluminium chloride in non-polar solvent: study of the initiation mechanism

Abstract

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.

Demonstration of the Existence of Long‐Lived Species in the Cationic Polymerization of 1,3‐Pentadiene Initiated by Aluminium Trichloride in Non Polar Solvent

“…After 17 h, the active species content was found to be lower, which was explained by an elimination reaction of SMe 2 on hindered species. The most important result is that, more particularly after 2 h of polymerization time, the active species concentration is of the same order of magnitude as the AlCl 3 concentration, which supports initial findings on direct initiation 2…”

“…From assumptions of the values of the rate constants ( k p , k t , k −t , k t′ and k r ), iterations were performed on these constants until the theoretical yields coincided at best with the experimental values. Based on a direct initiation mechanism already demonstrated in hexane2 and confirmed here in pentane, the initial active centers concentration, [C + ] 0 , was assumed to be equal to 1.15 × 10 −2 mol/L, that is to say, to [AlCl 3 ] 0 /2. The accuracy of the calculations was estimated for each modeling in order to determine the best system describing the experimental kinetics.…”

“…The investigations began by an improvement of the knowledge of the exact role of the Lewis acid. It was first shown that a direct initiation mechanism was operating,2 then that the cross‐linked fraction was mainly (but not exclusively) due to the insoluble part of the Lewis acid,3 and that quantitative evaluation of the unsaturation content by the means of 1 H and 13 C NMR spectroscopy provided access to the extent of isomerization and cyclization 4. The present paper is devoted to a better understanding of the kinetics and of the fate of the active species.…”

Cationic Polymerization of Dienes. 5. Study of the Polymerization of 1,3-Pentadiene cis/trans Isomers and Evidences of the Origins of the Insoluble Fraction

“…Nuclear Magnetic Resonance (NMR). 1 H and 13 C spectra were recorded on a Bruker Avance 300 MHz. 13 C measurements were performed using an inverse gate procedure (no NOE), allowing a quantitative determination of the carbon unsaturation loss.…”

“…[1][2][3] The polymer structure is complicated by the different microstructures of the monomer units (1,4-, 1,2-, and 3,4-polymerizations), by the involved stereochemistry (cis and trans enchainments) and by the occurrence of various side reactions like cyclization, double bond isomerization, termination, etc. [1][2][3] The aim of this work is to achieve a better understanding of the different mechanisms involved in the polymerization of this monomer, which is generally composed of a mixture of cis and trans isomers, the cost of pure isomers being expensive. This polymerization is very sensitive to experimental conditions (polarity of the solvent, nature of the initiator, monomer concentration, temperature, ...).…”