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

Abstract

Summary: A kinetic study of the polymerization of a mixture of 1,3‐pentadiene isomers initiated by AlCl3 was carried out in pentane at −10 and 20 °C. A second apparent monomer order was found mainly at room temperature and was explained by a complexation of propagating active centers by the polymer, the true monomer order being first. This apparent order did not result from the presence of the two isomers in the monomer mixture. Kinetic simulations confirmed this interpretation and pointed out the fact that the interaction between the polymer and the active centers was stronger at −10 °C, thus limiting the polymer conversion at this temperature. The novelty of these findings lies in the fact that the inactive complexed centers can be activated by reaction with the monomer, providing active species when necessary. The existence of active centers even after a long reaction time at room temperature, and the reactivation of the complexed centers, was evidenced by incremental monomer addition and by the formation of sulfonium ions after quenching the polymerization by an excess of dimethyl sulfide. The latter were characterized by 1H NMR spectroscopy.

A new insight into the mechanism of 1,3‐dienes cationic polymerization. II. Structure of poly(1,3‐pentadiene) synthesized with tBuCl/TiCl4 initiating system

“…Unsaturation of PPD‐1, calculated through the comparison of intensities of protons or carbon atoms in olefinic and aliphatic regions of 1 H and 13 C NMR spectra, (a) were 89 and 91%, respectively. It should be noted that these values of unsaturation are the ones of the highest for PPDs synthesized by cationic polymerization . Owing to the low content of saturated structures in PPD‐1 sample, their structure is not investigated in this study.…”

“…PPDs synthesized by cationic polymerization possess the most complicated microstructure of the polymer chain . Cationic PPDs are characterized by reduced unsaturation, which is explained either by chain transfer to polymer with the formation of branched structures or by intramolecular cyclization . The literature data on the microstructure of unsaturated part of polymer chain of cationic PPDs are quite ambiguous.…”

“…On the other hand, in a series of publications, along with aforementioned units, the significant amount of 3,4‐ , and cis −1,4‐units was identified in the structure of cationic PPDs, whereas the units with inverse monomer addition were not detected. Finally, in known studies devoted to the investigation of microstructure of cationic PPDs, only the signals of methyl carbon atoms were identified in 13 C NMR spectra, whereas data on position of the signals of other carbon atoms of corresponding structural units were almost absent. Moreover, the nature of head and end groups of cationic PPDs was investigated only in a few studies (b), and it was only reported that PPDs synthesized in the presence of AlCl 3 contained from 0.018 to 0.4% of chlorine, but the structure of chlorine‐containing units was not identified.…”

“…[10][11][12][13] Then, 13 C NMR spectroscopy was chosen as a powerful tool for analysis of the microstructure of stereoregular PPDs. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] The signals of carbon atoms in cis21, 4, 12,14,15,18 trans21,4, 14,15,18,19 trans21,2, 12, [14][15][16]19 and cis21,2 17 were identified in 13 C NMR spectra. However, data on the presence of 3,4-units in stereoregular PPD were not so unambiguous.…”

“…3,11,18,29 Cationic PPDs are characterized by reduced unsaturation, which is explained either by chain transfer to polymer with the formation of branched structures 3,[18][19][20][21][22] or by intramolecular cyclization. 11,[24][25][26][27][28][29][30] The literature data on the microstructure of unsaturated part of polymer chain of cationic PPDs are quite ambiguous. Particularly, it was found that cationic PPDs consist of trans21,4, trans21,2, and cis21,2 units.…”