Modifications of Ziegler-Natta Catalysts by Lewis Acids for the

Modifications of Ziegler-Natta Catalysts by Lewis Acids for the
Polymerization of Propylene
Vincent MONTEIL,* David RIBOUR, Roger SPITZ
Université de Lyon, CNRS / C2P2- LCPP team / BP2077, F-69616 Villeurbanne, France
email: [email protected]
Polyethylenes and polypropylenes represent approximately 50wt% of polymers with a fast
continuous growth. The “multi-site” character of Ziegler-Natta heterogeneous catalysts (based
on TiCl4 supported on MgCl2) has favoured their development with a good compromise between
polymer processability of polymers and physical properties and has led them to dominate the
manufacture of polyolefins (~50% of polyethylenes and ~100% of polypropylenes)1 but now it
limits the access to polymer ultimate properties which have been made popular by single-site
catalysis (e.g. metallocenes). In spite of considerable research efforts the way of operating of
these catalysts is far away to be well understood, giving no easy ways to go closer to a single-site
behaviour and to surpass the present properties.
From their observed collective behaviour we assumed a new model of active sites based on a
“cluster” organization of titanium atoms.2,3 This “cluster” hypothesis has led us to investigate
simple and versatile treatments of catalysts with Lewis acids (MCln) before the
polymerization.4,5 Treatments by various Lewis acids of conventional precatalysts evidence
various influences of modifications on activity and selectivity or molecular weight distribution
depending on the nature of Lewis acid (Figure 1). 4,5 Following orders can be established: BCl3
>> SnCl4 > SiCl4 >> SbCl5 > GaCl3 regarding activity and SnCl4 ~ SiCl4 >> BCl3 > SbCl5 >>
GaCl3 regarding tacticity. The most significant increase of Tm was observed with SnCl4 (Tm =
165.6 °C). Molecular weight distribution can be narrowed using SiCl4, SnCl4 and SbCl5 while it
is almost unchanged with other Lewis acids.
productivity
(g/g/90min)
tacticity (I.I. %)
12000
100
99,5
10000
99
98,5
8000
98
6000
97,5
97
4000
96,5
96
2000
95,5
0
95
ref.
1
ref. +
BCl3
ref. +
SnCl4
ref. +
SiCl4
Figure 1. Influence of treatments by various
Lewis acids on catalyst productivity and
selectivity in the propylene polymerization
(catalyst: TiCl4 / phthalate / MgCl2 + AlEt3 /
silane, T = 70°C, 4 bar propylene, Al/Ti = 250).
ref. + ref. +
GaCl3 SbCl5
Mulhaupt, R. Macromol. Chem. Phys. 2003, 204, 289. 2 Ribour, D.; Bollack-Benoit, V.;
Monteil, V.; Spitz, R. J. Polym. Sci. Part. A, 2007, 45, 3941. 3 Ribour, D.; Monteil, V.; Spitz, R.
J. Polym. Sci. Part. A 2008, 46, 5461. 4 Ribour, D.; Monteil, V.; Spitz, R. J. Polym. Sci. Part. A
2009, 47, 5784. 5 Ribour, D.; Monteil, V.; Spitz, R. J. Polym. Sci. Part. A 2010, 48, 2631.