Chain Walking in the AlCl₃Catalyzed Cationic Polymerization of α‐Olefins

Abstract

Continuing efforts aimed at performing the 1‐decene polymerization to low viscosity polyalphaolefins (PAO)s using a less hazardous AlCl3 catalyst than boron‐based analogs, the basic mechanisms of this system were revealed in this research. In this aspect, neat AlCl3 and AlCl3/toluene were carried out to perform 1‐decene polymerizations. Microstructure analyses of the as‐synthesized oils revealed low molecular weight (708 vs. 1529 g/mol), kinematic viscosity (KV100=6.4 vs. 22.2 cSt), and long chain branching (82.1 vs. 84.7) of PAO from the system containing toluene solvent. Furthermore, NMR analysis confirmed various types of short chain branch (SCB) with the inclusion of toluene ring in the structure of final PAO chains. Then, to shed light on the basic mechanisms of cationic polymerization of 1‐decene including: i) chain initiation, ii) chain transfer to the monomer, iii) isomerization of the carbocation via a chain walking mechanism (causes different SCB length), and iv) binding of toluene ring to the propagating PAO chain (to yield aromatic containing oligomers), molecular modeling at the DFT level was employed. The energies obtained confirmed the ease of carbocation isomerization and chain transfer mechanisms in toluene medium, which well confirms the highly branched structure experimentally obtained for related PAO.