Syndiotactic specific polymerization of styrene: driving energy of the steric control and reaction mechanism

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 I3C 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.

Synthesis of ethylene–styrene copolymer containing syndiotactic polystyrene sequence by trivalent titanium catalyst

“…Assignments of the resonances of the copolymer were carried out according to the previous reports. 8,18,[20][21][22][23][24][25] The spectrum of the insoluble part, obtained by TCE extraction of the crude product in Run 11, is shown in Figure 3. In addition to continuous homogeneous monomer sequences consisting of ethylene-ethylene (30.1 p.p.m.)…”

“…It has been traditionally believed that a trivalent titanium (Ti 3+ ) species is the predominant active species for the syndiotactic polymerization of styrene by the CpTiCl 3 /MAO type catalysts. [20][21][22][23][24][25][26] However, recent studies have indicated that a tetravalent titanium (Ti 4+ ) species is also generated and can similarly promote styrene polymerization in the CpTiCl 3 /MAO type catalyst system, independent of the Ti 3+ active species. [27][28][29][30][31] An analogous Ti 4+ species is believed to be the active species in olefin polymerization by metallocene-type catalyst systems (such as Cp 2 TiCl 2 /MAO).…”

Synthesis and characterization of elastoplastic poly(styrene-co-ethylene) using novel mono(?5-cyclopentadienyl) titanium and modified methylaluminoxane catalysts

“…Currently, mono( 5 -cyclopentadienyl)titanium complexes activated by MAO for syndiospecific polymerization of styrene are well known, [1][2][3][4][5] as well as for the polymerization of ethylene 6,7 and propylene. 8,9 The active species of mono( 5 -cyclopentadienyl)titanium/MAO catalyzing different monomers have been analyzed by various methods.…”

Effects of residual and external alkylaluminum on the synthesis of syndiotactic polystyrene with cyclopentadienyltitanium tribenzyloxide-methylaluminoxane catalyst

“…It has been suggested that the active species for styrene syndiotactic polymerization are in a trivalent state. 11,16 Higher residual TMA content in MAO (MAO1 or MAO2) favors the reduction of Ti in the catalyst system to Ti 3ϩ , promoting styrene polymerization more efficiently, whereas Ti in the catalyst system with MAO (MAO3 or MAO2Ј) containing less TMA remains mostly in a tetravalent state, resulting in much lower catalytic activities for the polymerization than the former. From the above investigations, it can be concluded that the residual TMA plays a deciding role in reduction of Ti in the catalyst system and promoting formation of the active centers for the styrene polymerization.…”