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

Abstract

The cationic polymerization of 1,3-pentadiene isomers initiated by AlCl3 was investigated in nonpolar solvent. It was shown that the polymerization was very sensitive to the initial monomer composition (proportion between the cis and trans isomers). The cis isomer favors the cross-linking reactions and double bond isomerization, whereas the trans isomer induces more cyclization. However, the behavior of the mixture of the two isomers cannot be simply deduced from a linear combination of the behavior of each isomer independently considered. Some polymerizations were realized in different alkanes (pentane, hexane, heptane, and decane). Despite similar polarity, it was observed that the higher the solvent molecular weight, the lower the total polymerization yield. These results were assigned to a different solubility of the Lewis acid and of polymer chains in the different solvents investigated. Finally, two origins of the cross-linked polymer were identified: the heterogeneity of the polymerization medium and intermolecular reactions of the active species with the polymer.

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

“…This fraction was due to the partial solubilization of the Lewis acid in pentane and to intermolecular reactions which were favored by a concentrated medium and high polymerization times. [3] This last point was confirmed by the last experiment (run 9), for which the molar mass drastically fell. This fact was explained by the intermolecular reactions responsible for the polymer cross-linking occurring on the macromolecular chains having the highest molar mass.…”

“…The analysis of the microstructure of the linear units in the polymerization of the cis-and trans-1,3-pentadiene mixture, published in a previous paper, [3] showed that the cisactive centers were of much lower concentration than the trans ones. Thus, the following simulations were carried out assuming the exclusive existence of one kind of active species.…”

“…This fact was explained by the intermolecular reactions responsible for the polymer cross-linking occurring on the macromolecular chains having the highest molar mass. [3] The evolution of I. F. showed that until 10 h the soluble polymer was produced more quickly.…”

“…After two hours of polymerization of the initial amount of monomer, the increment was introduced and the system was allowed to polymerize 2 h more (time quoted in Table 2, ''2 þ 2'': run 2) or 16.5 h more (time quoted in Table 2, ''2 þ 16.5'': run 3). Knowing that the yield of run 1 is equal to 70% and that the yield of the IMA polymerization is equal to 129% after 4 h of reaction and to 172% after 18.5 h, it is easy to calculate that the system polymerized again after the introduction of the monomer increment with a further yield of 59% in two hours and of 102% in 16.5 h. The value of 102% is not due to an experimental error.…”

“…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.…”