Cyclo‐ and cyclized diene polymers. XVI. Nature of the active species and a proposed mechanism of cyclopolymerization of isoprene with catalysts containing ethylaluminum halides

Abstract

The polymerization of isoprene with C2H5AlCl2 to yield solid cyclopolyisoprene is markedly accelerated by the addition of TiCl4. The polymer yield passes through a maximum on increasing the catalyst reaction time with or without monomer present. The active species are probably cations formed by dissociation of the reaction product of C2H5AlCl2 and TiCl4. The polymerization of isoprene with (C2H5)2AlX–TiCl4 (X = F, Br, Cl) has maximum activity at an Al/Ti mole ratio of 0.75 corresponding to conversion of R2AlX to RAIX2 which then reacts with remaining TiCl4. A proposed mechanism of cyclopolymerization of conjugated dienes involves monomer activation, i.e., conversion to cation radical by one‐electron transfer to catalyst cation which is itself neutralized, addition of cation end of monomer cation radical to terminal or internal unsaturation of fused cyclohexane polymer chain, one‐electron transfer from “neutral” catalyst to cation on polymer chain which is then transformed to a diradical which undergoes coupling to form a cyclohexene ring. The mechanism of the “living” polymerization involves addition of catalyst‐activated monomer to a “dead” polymer with a terminal cyclohexene ring and regeneration of the active catalyst.

Cyclo- and Cyclized Diene Polymers. XXII. Kinetics of Cyclopolymerization of Isoprene with C2H5AlCl2+ TiCl4Catalyst

“…Table 2 the contents of tolyl moieties in cyclopolyisoprenes prepared under various conditions. When comparing the aromatic residue content with molecular weight it is seen that one polymer molecule must contain more than one aromatic nucleus, in accordance with previous results [3,4]. Thus, in addition to chain transfer with the solvent, other reactions leading to the incorporation of the solvent residues into the macromolecule also occur.…”

“…Thus, in addition to chain transfer with the solvent, other reactions leading to the incorporation of the solvent residues into the macromolecule also occur. The mechanism of such reactions has already been proposed [3,4].…”

“…Ethylaluminum dichloride may react in the dimeric form so that the structure of the resultant complex may also be different [3].…”

“…Reaction (1) is thus followed by the initiation step: The actual form of the (TiCI3) moiety is unknown. It may represent one of the possible forms proposed earlier [3]. The chain growth proceeds through the addition of further monomer to the complexed monomer cation-radical.…”

Reactions Between AIRCl2and Ti (OR)4and Activity in Diolefin Polymerization

“…It has been reported that aluminum alkyl dichloride is not a stereospecific catalyst for the polymerization of diolefins with either TiC14 or P-TiC13 [2].…”