JOURNAL OF CATALYSIS 121, 248-261 (1990) Modification of Olefin Polymerization Catalysts. III. A 130 CP-MAS NMR Study of Adsorption of Silyl Ethers on MgCI2-Supported Zieg ler-Natta Catalysts TUULA T. PAKKANEN,* EILA VAHASARJA,* TAPANI A. PAKKANEN,* EERO IISKOLA,~ AND PEKKA SORMUNEN~ *Department of Chemistry, University of Joensuu, SF-80101 Joensuu, Finland; and ~fPolyolefins R & D, Neste Chemicals, SF-06850 Kulloo, Finland Received February 9, 1989 A 13C CP-MAS NMR and elemental analysis study of adsorption and interaction of silyl ethers, RSi(OMe)3 (R = Et, Ph, OMe), as internal and external electron donors with MgC12-supported Ziegler-Natta catalyst has been carried out. A chemical activation of anhydrous MgC12 with EtOH and A1Et3 produces a high-surface-area support stabilized by an organoaluminium compound, A1Et2(OEt). In a treatment of the aluminium-modified MgCI2 support with silyl ether, the alumin- ium surface complex is retained and silyl ether is almost totally incorporated into the support. ~3C CP-MAS NMR data of the methoxy region indicate that a mobile liquid-like silyl ether species dominates, except in the case of Si(OMe)4, where a more strongly bound species is also present on the support. TIC14 treatment removes the weakly adsorbed silyl ether species, leaving a species which is attributed to an aluminium-bound silyl ether surface complex. No evidence of titanium- bound silyl ether species was found in the solid state or in solution where TIC14 undergoes with silyl ethers an exchange reaction forming a yellow solid identified as [TiC12(OMe);]x. Activation of the catalyst with A1Et3 at a high AI:Ti ratio produces a material with a low silyl ether coverage showing a weak methoxy signal in ~3C CP-MAS. The linewidths of the observed signals in ~3C CP- MAS NMR are in the range 5-10 ppm at every stage of preparation of the catalyst, indicating heterogeneity of the coordination sites on the surface of chemically activated MgClz. © 1990 AcademicPress, Inc. INTRODUCTION High activity and stereospecificity are the typical characteristics of the third-gen- eration supported Ziegler-Natta catalysts for a-olefin polymerization (1-3). These catalysts comprise a solid catalyst, MgC12/ TiC14/electron donor, and a cocatalyst, an aluminium alkyl complexed with an elec- tron donor. The role of the electron donor, typically an organic Lewis base, in these high-activ- ity catalysts is not very well understood. The electron donor has been suggested to have several functions, such as to complex or to react with MgC12, TIC14, and the alu- minum alkyl, stabilizing the MgC12 crystal- lites, and to inactivate the nonstereospe- cific polymerization sites thus raising the isotactic index (4-8). Recent studies (9, 10) 0021-9517/90 $3.00 Copyright © 1990 by AcademicPress, Inc. All fightsof reproductionin any form reserved. show that in the heterogeneous catalyst there are a variety of active sites with dif- ferent stereospecificity and Lewis acidity. The role of an internal base seems to be in controlling the stereochemistry of the cata- lyst. The way by which the external base affects the stereospecificity is proposed to be dual, either a poisoning or an activation. The interaction of the free, uncomplexed base with the active sites seems to cause a decrease in isotactic productivity. On the other hand, the base-alkyl metal complex is proposed to be responsible for the activa- tion effect. Evidence for the presence of Lewis base in the environment of the active site has been found (10). Several methods, including polymeriza- tion kinetics (11-14), elemental analysis (6), GC-MS (5), EPR (15), X-ray analysis (16), and IR spectroscopy (17, 18) have 248