Véronique Pasquet

Improvement of supported catalysts for syndiotactic polymerization of styrene

The catalytic system Ti(OBu) 4 in combination with methylaluminoxane (MAO) was tested for the syndiospecific polymerization of styrene. A comparison was established between this homogeneous catalytic system and the same one supported on silica or alumina. An attempt was made to introduce a tether between the support and the active species to enhance both productivity and syndiospecificity. These tethers consisted of diols with different lengths. At last, the catalytic system Zr(OBu) 4 was supported on silica or alumina with MAO as a cocatalyst and was tested under the same conditions as other catalysts. This study reveals that Ti(OBu) 4 supported on silica enhances the productivity and leads to higher molecular weights, while the addition of a diol does not result in any enhancement compared to the silica-supported catalyst. On the contrary, alumina alone does not seem to be a good support for Ti(OBu) 4 , while introducing a short diol such as ethylene glycol leads to a great enhancement of both productivity and syndiospecificity. As reported in the literature, Zr(OBu) 4 always leads to much lower productivities than Ti(OBu) 4 .

Optimization of the Polymerization Parameters for Syndiotactic Polymerization of Styrene Using Supported Catalysts

The two catalytic systems Ti(OBu) 4 and CpTiCl 3 in combination with methylaluminoxane (MAO) were tested and compared in syndiotactic polymerization of styrene. In homogeneous conditions, CpTiCl 3 gives higher productivities than Ti(OBu) 4 . The productivity of CpTiCl 3 increases continuously with the Al/Ti ratio. On the contrary, confirming previous results, the productivity of Ti(OBu) 4 presents an optimum for an Al/Ti ratio of about 230. To optimize the syndiotactic polymerization of styrene using these supported catalysts, different parameters were examined: we show that a high concentration of MAO for heterogeneous conditions is necessary to ensure a good reproducibility of the polymerization, the role of transfer agent of the MAO was then demonstrated. Polymerizations carried out at different temperatures show that 50°C is a good compromise: when the temperature is raised the productivity increases but the syndiotacticity drops. At 50°C, the productivity is high enough and the syndiotacticity is above 90%, at 60°C, the productivity is a little higher but the syndiotacticity drops below 90%. Increasing the temperature does not influence the molecular weights showing that supporting Ti(OBu) 4 or CpTiCl 3 will stabilize the active species. As hydrogen behaves as a transfer agent for the conventional Ziegler catalysts, we carried out some experiments adding hydrogen during the polymerization. Indeed, the molecular weights are lowered. The melting points of the polymers depend as expected on the syndiotacticity and in a lower extent on the molecular weights.

Solid State Polycondensation in Dispersed Medium of 11-Aminoundecanoic Acid

The polycondensation of 11-aminoundecanoic acid was carried out in the solid state in dispersed medium: Decalin which is an inert saturated cyclic hydrocarbon and does not react whith the monomer and the condensation by product, water, was added to the monomer. In order to avoid a coagulation of the reaction mixture, an original strategy was developed using a liquid-solid dispersion instead of a liquid-liquid dispersion as described in the few studies reported in the literature for the polycondenstation of this monomer. A liquid-liquid suspension step was used at the early beginning of the reaction in order to melt, disperse and break the crystallinity of the monomer, then, the liquid droplets were solidified by cooling. During the polycondensation, the temperature was raised in successive steps in order to maintain the particles in the solid state. With a convenient treatment, it was possible to obtain a polymer powder with a defined particle size distribution and to reach fairly high molecular weights.