The stereoregularity of polystyrenes prepared in the presence of different syndiotactic specific homogeneous catalysts, at different temperatures and monomer concentrations, has been evaluated by C-13 NMR. It is confirmed that the statistical model of the stereospecific propagation is first-order Markovian. The stereoregularity of the polymers decreases 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 titanium based catalysts. Polymerization of substituted styrenes is increasingly stereospecific in the order p-chlorostyrene < styrene < p-methylstyrene. The results strongly support the polyinsertion mechanism proposed in a previous paper by some of us.
Syndiotactic Specific Polymerization of Styrene - Driving Energy of the Steric Control and Reaction-mechanism
LONGO, Pasquale;PROTO, Antonio;ZAMBELLI, Adolfo
1995-01-01
Abstract
The stereoregularity of polystyrenes prepared in the presence of different syndiotactic specific homogeneous catalysts, at different temperatures and monomer concentrations, has been evaluated by C-13 NMR. It is confirmed that the statistical model of the stereospecific propagation is first-order Markovian. The stereoregularity of the polymers decreases 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 titanium based catalysts. Polymerization of substituted styrenes is increasingly stereospecific in the order p-chlorostyrene < styrene < p-methylstyrene. The results strongly support the polyinsertion mechanism proposed in a previous paper by some of us.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
