1 research outputs found
Mechanism of Isotactic Styrene Polymerization with a C<sub>6</sub>F<sub>5</sub>‑Substituted Bis(phenoxyimine) Titanium System
We report a combined, experimental and theoretical, study
of styrene
polymerization to clarify the regio- and stereocontrol mechanism operating
with a C<sub>6</sub>F<sub>5</sub>-substituted bisÂ(phenoxyimine) titanium
dichloride complex. Styrene homopolymerization, styrene–propene
and styrene–ethene–propene copolymerizations have been
carried out to this aim. A combination of <sup>13</sup>C NMR analysis
of the chain-end groups and of the microstructure of the homopolymers
and copolymers reveals that styrene polymerization is highly regioselective
and occurs prevalently through 2,1-monomer insertion. DFT calculations
evidenced that steric interaction between the growing chain and the
monomer in the transition state insertion stage is at the origin of
this selectivity. The formation of isotactic polystyrene with a chain-end
like microstructure is rationalized on the base of a mechanism similar
to that proposed for the syndiospecific propene polymerization catalyzed
by bisÂ(phenoxyimine) titanium dichloride complexes. Finally, a general
stereocontrol mechanism operative in olefin polymerization with this
class of complexes is proposed