SYNDIOTACTIC SPECIFIC POLYMERIZATION OF STYRENE - DRIVING ENERGY OF THE STERIC CONTROL AND REACTION-MECHANISM

The stereoregularity of polystyrenes prepared in the presence of diffe rent syndiotactic specific homogeneous catalysts, at different tempera tures and monomer concentrations, has been evaluated by C-13 NMR. It i s confirmed that the statistical model of the stereospecific propagati on is first-order Markovian. The stereoregularity of the polymers decr eases while increasing the polymerization temperature and is affected by the concentration of the monomer, by the ligands of the transition metal precursor of the catalyst, and is higher in the presence of tita nium based catalysts. Polymerization of substituted styrenes is increa singly stereospecific in the order p-chlorostyrene < styrene < p-methy lstyrene. The results strongly support the polyinsertion mechanism pro posed in a previous paper by some of us.