Cationic polymerization of isobutylene with DCC/AlCl3 initiating system

The cationic polymerization of isobutylene (III) by utilizing difunctional initiator dicumyl chloride (DCC) in conjunction with coinitiator AlCl3 was carried out in CH2Cl2 /Hex (40/60, V/ V) solvent mixtures in the absence or in the presence of 2,6-dimethylpyiidine (DMPy) and triphenylamine (TPA) respectively. The effects of concentrations of DCC, electron donor and AlCl3, on monomer conversion, molecular weight and molecular weight distribution (MWD) of the product polyisobutylene (PIB) were investigated systematically. The small amount of water in the polymerization system in conjunction with AlCl3 induced a conventional uncontrolled rapid polymerization of 113 and led to polyisobutylene with broad molecular weight distribution. It is found that the GPC trace of resultant polymer obtained by DCC/H-2 O/AlCl3 system exhibit a bimodal distribution, which was attributed to the competition of initiation from two different active centers, i.e., H+ AlCl3 OH- (A) and AlCl4 (-+) C(CH3)(2)C6H4 (CH3)(2)C+ - AlCl4 (B) The initiation from active center (B) increased in the polymerization system with an increase in DCC concentration. A large dosage of DCC (DCC/H2O = 5.3) was needed to decrease the initiation from active center (A) effectively, and the polymer with low molecular weight (about 1.8 x 10(4)) was obtained. According to the characterization results of GPC, NMR and UV, both the initiation efficiency of DCC and molecular weight of polymer increased and MWD narrowed by addition of small amount of TPA or DMPy. The mechanistic role of TPA or DMPy was to decrease the uncontrolled initiation of proton from active center (A) and the chain transfer reaction to monomer. The monomer conversion decreased, but the initiation efficiently increased, and MWD narrowed with increasing of TPA or DMPy concentration. The initiation from active center (A) could be suppressed at high DCC concentration or even at low DCC concentration in the presence of TPA or DMPy. A desirable cationic polymerization of IB would be achieved with DCC/AlCl3 initiation system in the presence of adequate amount of TPA or DMPy, and polyisobutylene with relatively high molecular weight and relatively narrow unimodal molecular weight distribution could be obtained.