Cationic polymerization of isoprene using zinc halides as co‐initiators: towards well‐defined oligo(isoprene)s under mild conditions

Abstract

The activity of ZnX2‐based initiating systems (X = Cl, Br, I) in the cationic polymerization of isoprene was studied. The highest activity was achieved when co‐initiator (ZnX2) was solubilized in a minimal amount of strongly coordinating solvent such as diethyl ether or acetone and when trichloroacetic acid was used as an initiator. It is shown that the polymerization rate increased in the series ZnI2 < ZnCl2 < ZnBr2. An increase of initiator concentration and temperature also led to an increase of the polymerization rate. The obtained polyisoprenes did not contain high‐molecular‐weight and insoluble fractions and were characterized by low number‐average molecular weight and relatively narrow molecular weight distribution. Unsaturation of polyisoprene decreased with an increase of monomer conversion and reaction temperature. The unsaturated part of the polyisoprene chain possessed predominantly 1,4‐trans microstructure with regular and inverse addition, whereas the 1,2‐ and 3,4‐isomers were present as minor components. It is shown that the synthesized low‐molecular‐weight polyisoprenes are effective plasticizers for rubber compounds in the manufacture of tyres. © 2012 Society of Chemical Industry

Comprehensive structural characterization of polyisoprene synthesized via cationic mechanism

“…Moreover, the cyclic structures as well as the terminal conjugated isoprene units were also reported. In other publications, the presence of such structural units was not observed . The structure of head and end groups of the polymer chain of cationic polyisoprene is reported in several recent publications, but data about their content is absent …”

“…Isoprene was washed by water, dried on NaX molecular sieves and then distilled over CaH 2 in argon atmosphere. The content of trace impurities in isoprene was reported earlier . CH 2 Cl 2 (Biosolve, 99.9%) and tert ‐butyl chloride ( t BuCl; Fluka, >99.5%) were distilled over CaH 2 in argon flow before use.…”

“…Polymerizations were carried out under an argon atmosphere in baked glass ampoules of total volume of 12 mL equipped with magnetic stirrer bar and a septum. The detailed description of polymerization experiments was reported earlier . The polyisoprene samples CPI‐1 and CPI‐2 were synthesized with t BuCl/TiCl 4 initiating system in CH 2 Cl 2 .…”

“…In our previous publications devoted to the investigation of the structure of cationic polyisoprene synthesized using TiCl 4 , VOCl 3 , BF 3 OEt 2 , ZnCl 2 , and ZnBr 2 as cointitators, only three structural units was detected: trans ‐1,4‐, 1,2‐ and 3,4‐units . Trans ‐1,4‐ units with regular (head‐to‐tail) and inverse (head‐to‐head and tail‐to‐tail) enchainments were detected for the first time in work and the methods for their quantitative calculation were also proposed in same publication.…”

A New Insight into the Mechanism of 1,3‐Dienes Cationic Polymerization I: Polymerization of 1,3‐Pentadiene with tBuCl/TiCl4 Initiating System: Kinetic and Mechanistic Study

“…We showed recently that the use of excess of tert ‐butyl chloride ( t BuCl) toward Lewis acid (LA) ([ t BuCl]/[LA] = 10–1000 mol mol −1 ) allowed not only to increase significantly the reaction rate of 1,3‐dienes polymerization in the presence of zinc halides but also to synthesize well‐defined oligo(1,3‐diene)s ( ≤ 2000 g mol −1 ) with relatively narrow MWD (/ = 2–4), and without any IF . However, data concerning the influence of t BuCl on the activity of TiCl 4 ‐based initiating systems in the cationic polymerization of 1,3‐dienes are limited to describing two experiments on the isoprene polymerization with t BuCl/TiCl 4 initiating system at t BuCl to TiCl 4 molar ratio 0.9:1 and 1:1, respectively.…”