Acetic Acid → Isoprene Butadiene Isoprene

Participants

Reaction Conditions

Reaction Steps

Three hundred milliliters (ml) of purified, dried cyclohexane (99.5%, Phillips Petroleum) were introduced into a six-hundred milliliter stirred glass reactor. Air was removed from the reactor under vacuum and replaced by dry nitrogen. The reactor was equipped with an air driven stirrer, a pressure gauge, thermocouple, top surface inlet valve, dip tube feeder with valve, heating-mantle and variable controller and combination nitrogen/vacuum inlet with valve. Three ml of a 0.01M solution of bipyridyl in cyclohexane, 7.3 ml (90 mmol) of tetrahydrofuran freshly distilled from benzophenone ketyl and 1.8 ml (18 mmol) of purified isoprene were injected into the reactor. The temperature of the reactor and its contents was raised to 50° C. The solution was then titrated by addition of 1.6M butyl lithium until a persistent red color was obtained. Following this, 3.75 ml of 1.6M butyl lithium was injected into the reactor in order to initiate polymerization of the isoprene. The reaction was allowed to run for one hour, after which 47.5 g of purified butadiene were pressured into the reactor at a rate such that the reaction temperature did not exceed 70° C. After one hour, the reactor pressure had returned to its initial level and the formation of the second block of the copolymer was completed. Isoprene (1.8 ml, 18 mmol) was again injected into the reactor to allow for the formation of the third and final block of the triblock polymer. After one hour, 0.35 ml of acetic acid (4.5 mmol) were injected into the reactor to quench the triblock living anion. The color of the reaction mixture changed from a dark amber to colorless immediately. The mixture was cooled to room temperature, filtered through alumina/Celite, an anti-oxidant, Irganox 1076 from Ciba-Geigy (100 ppm based on dry polymer) was added and solvent was removed under reduced pressure to yield a triblock polymer of about 8400 molecular weight as a clear, colorless, viscous fluid. Infra-red analysis (Fourier Transform) showed the butadiene center block to possess 55% (1,2)- and 45% of (1,4)-microstructure.

Provenance & Evidence