CATIONIC POLYMERIZATION OF ISOBUTYLENE COINITIATED BY AlCl3 IN THE PRESENCE OF ETHYL BENZOATE

The cationic polymerizations of isobutylene (IB) coinitiated by AlCl3 were carried out in solvent mixture of n-hexane/methylene dichloride (n-hex/CH2Cl2) of 60/40 V/V in the presence of ethyl benzoate (EB) at various temperatures range from -80 degrees C to -30 degrees C. The effects of EB concentration ([EB]) and polymerization temperature on monomer conversion, weight-average molecular weight (M-w) and molecular weight distribution (MWD, M-w/M-n) of polyisobutylene (PIB) products were investigated. The rate of polymerization decreased while M-w of PIB products increased with increasing [EB]. The polymers with high molecular weight could be prepared in the presence of a suitable amount of EB. Significantly, the polymers with high M-w of 80.2 x 10(4) and 65.4 x 10(4) could be produced at -80 degrees C and -70 degrees C at [EB] = 0.24 x 10(-3) mol/L respectively, which were much higher than that (M-w = 57.9 x 10(4)) of PIB prepared at -100 degrees C in the absence of EB. A simple but effective method for preparing the high molecular weight polyisobutylenes was developed in this work. It has been also found that the activation energy for propagation (E-p) depended on the polymerization temperature range in the presence of EB. An obvious inflection of the linear plots of InXn versus 1/T-p occurred at the temperature range from -60 degrees C to -50 degrees C at four different concentrations of EB from 0.19 x 10(-3) mol/L to 0.33 x 10(-3) mol/L, and thus the inflection temperature (T-inf) was in the range of -60 degrees C to -50 degrees C. When [EB] was in the range of 0.24 x 10(-3) mol/L to 0.33 x 10(-3) mol/L, Ep was determined to be around -12 kJ/mol when the polymerization was carried out at temperatures from -80 degrees C to T-inf and to be around -28 kJ/mol at temperatures from T-inf to -15 degrees C respectively.