Anionic alkyllithium initiated polymerization of isoprene in continuous stirred tank reactors

Abstract

Isoprene was polymerized in the presence of the solvent, hexane, in two laboratory continuous stirred tank reactors (CSTR) of different size, using n-fcutyllithium as the initiator. The smaller reactor was made of stainless steel and had a volume of 0.04 lite r. The larger reactor was made of Pyrex glass and had a volume of 0.80 liter. Well stirred condition was very nearly achieved in both reactors at an agitator speed of 300 rpm. This was verified by performing residence time distribution experiments with glycerine-water solution and a polyisoprene solution in hexane. A total of thirteen experimental runs were performed. Monomer concentration was varied between 1.0 mole per lite r to 5.0 moles per lite r and initiator concentration between 0.005 mole per liter to 0.0171 mole per liter. The reaction temperature was 40°C for all runs except one, for which it was 42°C. The agitator speed was 300 rpm for all runs except one, for which it was 510 rpm. The mean residence time varied between 18 to 36 minutes. The mathematical models for n-butyllithium initiated polymerization of isoprene in the presence of solvents, hexane and benzene, proposed by Porter [1] and Magott [2], respectively, were modified to obtain better estimates of the weight average molecular weights. The modifications were based on the assumption that the rate of propagation was dependent on chain length. Empirical equations were also determined to represent the experimental molecular weight distributions obtained by Porter [1] and by Magott [2] in batch reactors. The reaction mechanism proposed by the modified model in hexane solvent was used to analyze the experimental results from the two CSTR's.