Journal of Applied Polymer Science, Vol.85, No.13, 2635-2643, 2002
Full-range kinetic study on bulk syndiotactic polymerization of styrene with homogeneous metallocene catalysis
By choosing a proper agitator and reinforcing its stirring shear, powdery syndiotactic polystyrene (sPS) is prepared in a bulk precipitation process with two homogeneous metallocene catalyst systems [Cp*TiX3/'MAO/TIBA (X = Cl or OPhOMe)]. A full-range kinetics study of the heterogeneous polymerization is performed in detail to produce this kind of powdery sPS in an industrial process. A typical curve of conversion versus time takes an S shape and an obvious acceleration phenomenon occurs in the middle stage of the polymerization, although the polymer-monomer gel is avoided. The viscous-average molecular weight of sPS goes through a peculiar increasing-decreasing-increasing change during the bulk polymerization process. These phenomena are viewed in terms of the two-phase polymerization mechanism and the overheating in particles during polymerization. The influence of the metallocene catalyst type and concentration, MAO/Ti ratio, triisobutyl aluminum (TIBA)/Ti ratio, and polymerization temperature on the polymerization kinetics are investigated. TIBA has dual effects on the polymerization. A small amount of TIBA in the catalyst system promotes polymerization, but more TIBA leads to a low molecular weight sPS.