1
08
M.L. Kantam et al. / Journal of Molecular Catalysis A: Chemical 240 (2005) 103–108
the polydispersity decreased, indicating the growth of the
existing polymer chains. Due to a possible blockage of
the active sites by the existing chains, few new polymer
chains are formed, limiting the diffusion of new monomer
molecules to the active moieties [18]. Thermal analysis and
IR analysis of the catalyst after use showed the presence
of polystyrene. Moreover, the surface area of the catalysts
2
after use is significantly reduced by 50–100 m /g for both
NA-MgO supported and NA-TiO2 supported catalysts. These
results explain the drop in the activity of the reused catalysts,
NA-MgO/MAO/Cp2ZrCl2 and NA-TiO2/MAO/Cp2ZrCl2 in
the styrene polymerization reaction.
Fig. 5. 13C NMR spectra of polystyrene prepared by cat 1.
4. Conclusions
Polymerization with CM-MgO-MAO and TiO2-MAO
(commercially available) supported Cp2ZrCl2 produces
Heterogeneous NA-MgO-MAO and NA-TiO2-MAO
polystyrene in negligible yield. CM-MgO-MAO-Cp2ZrCl2
is found to have A [activity (gps/mol Zr h)] < 50 and com-
mercial TiO2-MAO-Cp2ZrCl2 is found to have A [activity
supported bis (cyclopentadienyl) zirconium dichloride
(Cp2ZrCl2) catalysts are synthesized and used for stereos-
elective polymerization of styrene monomer. The supporting
process is confirmed by XPS and FTIR. Nanoparticle sup-
ported zirconocene catalysts gave higher yield of syndiotactic
styrene polymer with high Mn and Mw and narrow molecu-
lar weight distribution when compared with the other sup-
ported zirconocene catalysts. These heterogeneous catalysts
are reused for two cycles. Further experiments are in progress
on polymerization of ethylene.
(
gps/mol Zr h)] < 50 and they produce low molecular weight
polystyrene (<1000) with broader polydispersity (even with
720 molofAland1.602 molofZr)comparedtonanopar-
3
ticle supported catalysts. The higher activity of the supported
catalysts is attributed to the higher surface area of the nano
support because the accumulation of the catalyst and cocat-
alyst molecules is more on the surface (from XPS result).
Moreover, the uniformity of active centers present on the
nanoparticle surface during polymerization is much higher
than the ordinary support as is observed from XPS studies.
Therefore, the polymers obtained are with narrow molecular
weight distribution and low polydispersity.
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